10.8: Nutrition and Diet - Biology

10.8: Nutrition and Diet - Biology

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Learning Objectives

By the end of this section, you will be able to:

  • Explain how different foods can affect metabolism
  • Describe a healthy diet, as recommended by the U.S. Department of Agriculture (USDA)
  • List reasons why vitamins and minerals are critical to a healthy diet

The carbohydrates, lipids, and proteins in the foods you eat are used for energy to power molecular, cellular, and organ system activities. Importantly, the energy is stored primarily as fats. The quantity and quality of food that is ingested, digested, and absorbed affects the amount of fat that is stored as excess calories. Diet—both what you eat and how much you eat—has a dramatic impact on your health. Eating too much or too little food can lead to serious medical issues, including cardiovascular disease, cancer, anorexia, and diabetes, among others. Combine an unhealthy diet with unhealthy environmental conditions, such as smoking, and the potential medical complications increase significantly.

Food and Metabolism

The amount of energy that is needed or ingested per day is measured in calories. The nutritional Calorie (C) is the amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C. This is different from the calorie (c) used in the physical sciences, which is the amount of heat it takes to raise 1 g of water by 1 °C. When we refer to “calorie,” we are referring to the nutritional Calorie.

On average, a person needs 1500 to 2000 calories per day to sustain (or carry out) daily activities. The total number of calories needed by one person is dependent on their body mass, age, height, gender, activity level, and the amount of exercise per day. If exercise is regular part of one’s day, more calories are required. As a rule, people underestimate the number of calories ingested and overestimate the amount they burn through exercise. This can lead to ingestion of too many calories per day. The accumulation of an extra 3500 calories adds one pound of weight. If an excess of 200 calories per day is ingested, one extra pound of body weight will be gained every 18 days. At that rate, an extra 20 pounds can be gained over the course of a year. Of course, this increase in calories could be offset by increased exercise. Running or jogging one mile burns almost 100 calories.

The type of food ingested also affects the body’s metabolic rate. Processing of carbohydrates requires less energy than processing of proteins. In fact, the breakdown of carbohydrates requires the least amount of energy, whereas the processing of proteins demands the most energy. In general, the amount of calories ingested and the amount of calories burned determines the overall weight. To lose weight, the number of calories burned per day must exceed the number ingested. Calories are in almost everything you ingest, so when considering calorie intake, beverages must also be considered.

To help provide guidelines regarding the types and quantities of food that should be eaten every day, the USDA has updated their food guidelines from MyPyramid to MyPlate. They have put the recommended elements of a healthy meal into the context of a place setting of food. MyPlate categorizes food into the standard six food groups: fruits, vegetables, grains, protein foods, dairy, and oils. The accompanying website gives clear recommendations regarding quantity and type of each food that you should consume each day, as well as identifying which foods belong in each category. The accompanying graphic gives a clear visual with general recommendations for a healthy and balanced meal. The guidelines recommend to “Make half your plate fruits and vegetables.” The other half is grains and protein, with a slightly higher quantity of grains than protein. Dairy products are represented by a drink, but the quantity can be applied to other dairy products as well. provides extensive online resources for planning a healthy diet and lifestyle, including offering weight management tips and recommendations for physical activity. It also includes the SuperTracker, a web-based application to help you analyze your own diet and physical activity.

Everyday Connections: Metabolism and Obesity

Obesity in the United States is epidemic. The rate of obesity has been steadily rising since the 1980s. In the 1990s, most states reported that less than 10 percent of their populations was obese, and the state with the highest rate reported that only 15 percent of their population was considered obese. By 2010, the U.S. Centers for Disease Control and Prevention reported that nearly 36 percent of adults over 20 years old were obese and an additional 33 percent were overweight, leaving only about 30 percent of the population at a healthy weight. These studies find the highest levels of obesity are concentrated in the southern states. They also find the level of childhood obesity is rising.

Obesity is defined by the body mass index (BMI), which is a measure of an individual’s weight-to-height ratio. The normal, or healthy, BMI range is between 18 and 24.9 kg/m2. Overweight is defined as a BMI of 25 to 29.9 kg/m2, and obesity is considered to be a BMI greater than 30 kg/m2. Obesity can arise from a number of factors, including overeating, poor diet, sedentary lifestyle, limited sleep, genetic factors, and even diseases or drugs. Severe obesity (morbid obesity) or long-term obesity can result in serious medical conditions, including coronary heart disease; type 2 diabetes; endometrial, breast, or colon cancer; hypertension (high blood pressure); dyslipidemia (high cholesterol or elevated triglycerides); stroke; liver disease; gall bladder disease; sleep apnea or respiratory diseases; osteoarthritis; and infertility. Research has shown that losing weight can help reduce or reverse the complications associated with these conditions.


Vitamins are organic compounds found in foods and are a necessary part of the biochemical reactions in the body. They are involved in a number of processes, including mineral and bone metabolism, and cell and tissue growth, and they act as cofactors for energy metabolism. The B vitamins play the largest role of any vitamins in metabolism (Table 1 and Table 2).

You get most of your vitamins through your diet, although some can be formed from the precursors absorbed during digestion. For example, the body synthesizes vitamin A from the β-carotene in orange vegetables like carrots and sweet potatoes. Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins A, D, E, and K, are absorbed through the intestinal tract with lipids in chylomicrons. Vitamin D is also synthesized in the skin through exposure to sunlight. Because they are carried in lipids, fat-soluble vitamins can accumulate in the lipids stored in the body. If excess vitamins are retained in the lipid stores in the body, hypervitaminosis can result.

Water-soluble vitamins, including the eight B vitamins and vitamin C, are absorbed with water in the gastrointestinal tract. These vitamins move easily through bodily fluids, which are water based, so they are not stored in the body. Excess water-soluble vitamins are excreted in the urine. Therefore, hypervitaminosis of water-soluble vitamins rarely occurs, except with an excess of vitamin supplements.

Table 1. Fat-soluble Vitamins
Vitamin and alternative nameSourcesRecommended daily allowanceFunctionProblems associated with deficiency
A: retinal or β-caroteneYellow and orange fruits and vegetables, dark green leafy vegetables, eggs, milk, liver700–900 µgEye and bone development, immune functionNight blindness, epithelial changes, immune system deficiency
D: cholecalciferolDairy products, egg yolks; also synthesized in the skin from exposure to sunlight5–15 µgAids in calcium absorption, promoting bone growthRickets, bone pain, muscle weakness, increased risk of death from cardiovascular disease, cognitive impairment, asthma in children, cancer
E: tocopherolsSeeds, nuts, vegetable oils, avocados, wheat germ15 mgAntioxidantAnemia
K: phylloquinoneDark green leafy vegetables, broccoli, Brussels sprouts, cabbage90–120 µgBlood clotting, bone healthHemorrhagic disease of newborn in infants; uncommon in adults
Table 2. Water-soluble Vitamins
Vitamin and alternative nameSourcesRecommended daily allowanceFunctionProblems associated with deficiency
B1: thiamineWhole grains, enriched bread and cereals, milk, meat1.1–1.2 mgCarbohydrate metabolismBeriberi, Wernicke-Korsikoff syndrome
B2: riboflavinBrewer’s yeast, almonds, milk, organ meats, legumes, enriched breads and cereals, broccoli, asparagus1.1–1.3 mgSynthesis of FAD for metabolism, production of red blood cellsFatigue, slowed growth, digestive problems, light sensitivity, epithelial problems like cracks in the corners of the mouth
B3: niacinMeat, fish, poultry, enriched breads and cereals, peanuts14–16 mgSynthesis of NAD, nerve function, cholesterol productionCracked, scaly skin; dementia; diarrhea; also known as pellagra
B5: pantothenic acidMeat, poultry, potatoes, oats, enriched breads and cereals, tomatoes5 mgSynthesis of coenzyme A in fatty acid metabolismRare: symptoms may include fatigue, insomnia, depression, irritability
B6: pyridoxinePotatoes, bananas, beans, seeds, nuts, meat, poultry, fish, eggs, dark green leafy vegetables, soy, organ meats1.3–1.5 mgSodium and potassium balance, red blood cell synthesis, protein metabolismConfusion, irritability, depression, mouth and tongue sores
B7: biotinLiver, fruits, meats30 µgCell growth, metabolism of fatty acids, production of blood cellsRare in developed countries; symptoms include dermatitis, hair loss, loss of muscular coordination
B9: folic acidLiver, legumes, dark green leafy vegetables, enriched breads and cereals, citrus fruits400 µgDNA/protein synthesisPoor growth, gingivitis, appetite loss, shortness of breath, gastrointestinal problems, mental deficits
B12: cyanocobalaminFish, meat, poultry, dairy products, eggs2.4 µgFatty acid oxidation, nerve cell function, red blood cell productionPernicious anemia, leading to nerve cell damage
C: ascorbic acidCitrus fruits, red berries, peppers, tomatoes, broccoli, dark green leafy vegetables75–90 mgNecessary to produce collagen for formation of connective tissue and teeth, and for wound healingDry hair, gingivitis, bleeding gums, dry and scaly skin, slow wound healing, easy bruising, compromised immunity; can lead to scurvy


Minerals in food are inorganic compounds that work with other nutrients to ensure the body functions properly. Minerals cannot be made in the body; they come from the diet. The amount of minerals in the body is small—only 4 percent of the total body mass—and most of that consists of the minerals that the body requires in moderate quantities: potassium, sodium, calcium, phosphorus, magnesium, and chloride.

The most common minerals in the body are calcium and phosphorous, both of which are stored in the skeleton and necessary for the hardening of bones. Most minerals are ionized, and their ionic forms are used in physiological processes throughout the body. Sodium and chloride ions are electrolytes in the blood and extracellular tissues, and iron ions are critical to the formation of hemoglobin. There are additional trace minerals that are still important to the body’s functions, but their required quantities are much lower.

Like vitamins, minerals can be consumed in toxic quantities (although it is rare). A healthy diet includes most of the minerals your body requires, so supplements and processed foods can add potentially toxic levels of minerals. Table 3 and Table 4 provides a summary of minerals and their function in the body.

Table 3. Major Minerals
MineralSourcesRecommended daily allowanceFunctionProblems associated with deficiency
PotassiumMeats, some fish, fruits, vegetables, legumes, dairy products4700 mgNerve and muscle function; acts as an electrolyteHypokalemia: weakness, fatigue, muscle cramping, gastrointestinal problems, cardiac problems
SodiumTable salt, milk, beets, celery, processed foods2300 mgBlood pressure, blood volume, muscle and nerve functionRare
CalciumDairy products, dark green leafy vegetables, blackstrap molasses, nuts, brewer’s yeast, some fish1000 mgBone structure and health; nerve and muscle functions, especially cardiac functionSlow growth, weak and brittle bones
PhosphorousMeat, milk700 mgBone formation, metabolism, ATP productionRare
MagnesiumWhole grains, nuts, leafy green vegetables310–420 mgEnzyme activation, production of energy, regulation of other nutrientsAgitation, anxiety, sleep problems, nausea and vomiting, abnormal heart rhythms, low blood pressure, muscular problems
ChlorideMost foods, salt, vegetables, especially seaweed, tomatoes, lettuce, celery, olives2300 mgBalance of body fluids, digestionLoss of appetite, muscle cramps
Table 4. Trace Minerals
MineralSourcesRecommended daily allowanceFunctionProblems associated with deficiency
IronMeat, poultry, fish, shellfish, legumes, nuts, seeds, whole grains, dark leafy green vegetables8–18 mgTransport of oxygen in blood, production of ATPAnemia, weakness, fatigue
ZincMeat, fish, poultry, cheese, shellfish8–11 mgImmunity, reproduction, growth, blood clotting, insulin and thyroid functionLoss of appetite, poor growth, weight loss, skin problems, hair loss, vision problems, lack of taste or smell
CopperSeafood, organ meats, nuts, legumes, chocolate, enriched breads and cereals, some fruits and vegetables900 µgRed blood cell production, nerve and immune system function, collagen formation, acts as an antioxidantAnemia, low body temperature, bone fractures, low white blood cell concentration, irregular heartbeat, thyroid problems
IodineFish, shellfish, garlic, lima beans, sesame seeds, soybeans, dark leafy green vegetables150 µgThyroid functionHypothyroidism: fatigue, weight gain, dry skin, temperature sensitivity
SulfurEggs, meat, poultry, fish, legumesNoneComponent of amino acidsProtein deficiency
FluorideFluoridated water3–4 mgMaintenance of bone and tooth structureIncreased cavities, weak bones and teeth
ManganeseNuts, seeds, whole grains, legumes1.8–2.3 mgFormation of connective tissue and bones, blood clotting, sex hormone development, metabolism, brain and nerve functionInfertility, bone malformation, weakness, seizures
CobaltFish, nuts, leafy green vegetables, whole grainsNoneComponent of B12None
SeleniumBrewer’s yeast, wheat germ, liver, butter, fish, shellfish, whole grains55 µgAntioxidant, thyroid function, immune system functionMuscle pain
ChromiumWhole grains, lean meats, cheese, black pepper, thyme, brewer’s yeast25–35 µgInsulin functionHigh blood sugar, triglyceride, and cholesterol levels
MolybdenumLegumes, whole grains, nuts45 µgCofactor for enzymesRare

Chapter Review

Nutrition and diet affect your metabolism. More energy is required to break down fats and proteins than carbohydrates; however, all excess calories that are ingested will be stored as fat in the body. On average, a person requires 1500 to 2000 calories for normal daily activity, although routine exercise will increase that amount. If you ingest more than that, the remainder is stored for later use. Conversely, if you ingest less than that, the energy stores in your body will be depleted. Both the quantity and quality of the food you eat affect your metabolism and can affect your overall health. Eating too much or too little can result in serious medical conditions, including cardiovascular disease, cancer, and diabetes.

Vitamins and minerals are essential parts of the diet. They are needed for the proper function of metabolic pathways in the body. Vitamins are not stored in the body, so they must be obtained from the diet or synthesized from precursors available in the diet. Minerals are also obtained from the diet, but they are also stored, primarily in skeletal tissues.

Self Check

Answer the question(s) below to see how well you understand the topics covered in the previous section.

Critical Thinking Questions

  1. Weight loss and weight gain are complex processes. What are some of the main factors that influence weight gain in people?
  2. Some low-fat or non-fat foods contain a large amount of sugar to replace the fat content of the food. Discuss how this leads to increased fat in the body (and weight gain) even though the item is non-fat.

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  1. Factors that influence weight gain are food intake (both quantity and quality), environmental factors, height, exercise level, some drugs or disease states, and genes.
  2. Although these foods technically do not have fat added, many times a significant amount of sugar is added to sweeten the food and make it taste better. These foods are non-fat; however, they can lead to significant fat storage or weight gain because the excess sugar is broken down into pyruvate, but overloads the Krebs cycle. When this happens, the sugar is converted into fat through lipogenesis and stored in adipose tissues.



body mass index (BMI): relative amount of body weight compared to the overall height; a BMI ranging from 18–24.9 is considered normal weight, 25–29.9 is considered overweight, and greater than 30 is considered obese

calorie: amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C

minerals: inorganic compounds required by the body to ensure proper function of the body

vitamins: organic compounds required by the body to perform biochemical reactions like metabolism and bone, cell, and tissue growth

What Do We Know About Diet and Prevention of Alzheimer's Disease?

Can eating a specific food or following a particular diet help prevent or delay dementia caused by Alzheimer’s disease? Many studies suggest that what we eat affects the aging brain’s ability to think and remember. These findings have led to research on general eating patterns and whether they might make a difference.

The Mediterranean diet, the related MIND diet (which includes elements designed to lower blood pressure), and other healthy eating patterns have been associated with cognitive benefits in studies, though the evidence is not as strong as it is for other interventions like physical activity, blood pressure and cognitive training. Currently, researchers are more rigorously testing these diets to see if they can prevent or delay Alzheimer’s disease or age-related cognitive decline.

Principles of Nutrition and Balanced Diet

Food may be defined as any solid or liquid substance which when taken by the body provides it with necessary materials to enable it to grow, replace the worn-out and damaged parts and provide energy to function normally. The daily food intake has a direct influence on the health and well-being of an individual. Food is composed of different chemical elements.

Nutrients are molecules which the body uses to function appropriately and stay in a healthy condition.

It is the study of nutrients and their relationship with food and living beings.

The food that a person normally takes everyday.

Malnutrition means an incorrect or imbalanced intake of nutrients.

Means insufficient total intake of nutrients.

Basic dietary components:

There are five classes of basic components or nutrients:

(5) Minerals and trace elements.

The components under 1 to 3 are known as macronutrients, those under 4 and 5 are known as micronutrients.

Carbohydrates are not at all required in the diet. Yet, we consume large amounts of carbohydrates every day because they are the cheapest source of energy and easily available dietary sources. Carbohydrates are the main sources of energy to the body which provide about 70% of the daily calorie requirements. Carbohydrates, in addition to the supply of energy also serve as the components of cell mem­brane and receptors. Carbohydrates are very well synthesized in our body from non-carbohydrate sources.

Cellulose and stretch reflex:

Cellulose (polysaccharide) materials present in the diet form the bulk (fiber) of the food and cannot be digested by human beings because of the absence of the enzyme cellulase. The cellulose helps in the movement of the food through the G.I tract. The cellulose material of the diet absorbs the waste from large intestine and while doing so it stretches the wall of the large intestine and as a result, defecation takes place. This is called stretch reflex.

There is a metabolic disorder called diabetes mellitus wherein there is an increased level of glucose in the blood (hyperglycemia). Hyperglycemia affects the normal functioning of the kidney and brain leading to hypertension and other abnormalities. Hence, in diabetes mellitus patients, the blood glucose level should be kept under control, for which the carbohydrates should be restricted in the diet.

The energy requirements can be met with proteins and to a little extent by fats. But as human beings first and the foremost food i.e. milk tastes sweet due to the presence of a carbohydrate lactose, he has a craving for sweet and hence he should be supplied with some non-carbohydrate sweeteners.

Non-carbohydrate sweeteners:

Some of the non-carbohydrate sweeteners are saccharin, sodium cyclamate, monallin and aspartame. These sweeteners are also used in the milk powder supplied to children with lactose intolerance, wherein the milk is free from lactose but contains one of these sweeteners.

It is 400 times sweeter than table sugar. Saccharin is commercially used in large scales though it is banned scientifically at present. It is used as sweetener in diabetes and obesity. But it is harmful to human beings. When saccharin is given in large quantities in drinks and food it causes cancer. However as the risk is too low it is still used as an artificial non-calorie sweetener in the diet drinks specially of those who are diabetes.

It is 30 times sweeter than table sugar. It is a carcinogenic agent and has been banned from prepared foods.

It is 180 times sweeter than table sugar. It is a methyl ester of a dipeptide of two amino acids that normally occur in protein (i.e., aspartate and phenylalanine). As it is non-toxic, it is used as a sugar substitute in many foods. The sugar free tablets available in the market are all made up of aspartame.

It is a protein with a molecular weight of 11,000. It is 2100 times sweeter than table sugar. Its sweetness is due to the three dimensional conformation of the polypeptide. But this cannot be used in prepared foods because it looses its sweetness on heating or denaturation.

Fats are also not needed in our diet. But we consume it because of its high calorific values (1 g gives 9 Kcal) and also it can be easily stored with less amount of water and therefore occupy less space. These fats are also taken because of their essential fatty acid content. Essential fatty acids are those which cannot be synthesized in our body, hence they should be supplied through the diet.

They are ‘linoleic acid’ and ‘linolenic acids’. Arachidonic acid is also an essential fatty acid but it can be synthesized from linolenic acid. They are also a good source of fat soluble vitamins viz., A, D, E & K. Plant fats are superior to animal fats because they contain more of polyunsaturated fatty acids i.e. essential fatty acids and less of cholesterol. The cholesterol in the diet should be restricted because excess intake of cholesterol leads to its deposition in the tissues thereby causing atherosclerosis.

Proteins are needed for their content of certain amino acids that are essential to human body for the biosynthesis of proteins, body repair in adult and for body building and body repair in children. Human body proteins are made up of only 20 standard amino acids out of which nearly 10 amino acids can be synthesized in the body but the remaining 10 cannot be synthesized in the body hence they have to be supplied through the diet. Therefore they are known as essential amino acids.

The essential amino acids are:

M — Methionine (semi essential)

A — Arginine (semi essential)

The nutritional value of a protein depends on two factors:

(1) Its content of the essential amino acids

The amino acid content of all the proteins is not the same. One will be deficient in one amino acid and the other in another type of amino acid. Some proteins are not completely digested to liberate all the amino acid contents, ex. the protein rich portions of wheat grains are not completely digestible.

It is a condition in which the intake of protein nitrogen (AA) exactly balances the loss of nitrogen in the urine and faeces. If the intake is more than the output due to nitrogen retention as tissue protein then the subject is said to be in positive nitrogen balance. If the intake is less than the output (as in old age and illness) then the subject is said to be in negative nitrogen balance.

Biological value of protein:

The biological value of a protein is a factor that is inversely proportional to the amount of a given protein source that must be consumed to keep an adult human in nitrogen balance. If the protein taken in the diet has all the essential amino acids in good proportions, is completely digested and is completely absorbed then that protein is said to be a good protein or it is said to have 100% biological value.

A protein of cent percent biological value should also completely replace the nitrogen lost in the urine. Generally animal proteins have higher biological value than plant proteins, because the animal pro­teins are much alike the human proteins and hence they have more digestibility and absorbability, for example egg and milk portions have their biological values near 100% (94% & 96% respectively).

Most of the plant proteins have low biological values and are said to be poor proteins. If two vegetable proteins are taken in combination, called succotash, then this mixture of proteins will have good biolog­ical value (though not 100%). Ex. the corn proteins are low in lysine but contain adequate amounts of tryptophan whereas bean proteins contain adequate amounts of lysine but are low in tryptophan.

Neither is a good protein. But a mixture of the two is a good source of having balanced amino acids. If beans are taken in the breakfast and corn in the lunch (i.e. after 5-6 hours) then it will be of no biological value because amino acids cannot be stored. Therefore the biological value of vegetable proteins can be im­proved if taken along with animal proteins for the daily protein supply. It is recommended that 1/3 rd to 1/2 of the proteins may be derived from animal proteins like egg, meat and milk.

Protein sparing action of carbohydrates and fats:

Carbohydrates and fats spare the proteins and make then available for anabolic or constructive purpose. Carbohydrates and fats supply the required energy and so proteins will not take part in energy metabolism, especially in patients needing tissue repair, this action is seen.

Balanced Diet:

A balanced diet can be defined as the nutrients required for sustaining and keeping the human body in metabolic health. It can also be defined as nourishment (food) required for maintaining normal life. Balanced diet is one which contains all the food constitutes in proper proportion to meet the energy and nutritional requirements of the individual. The components of a well-balanced diet will vary depend­ing on age, sex, physiological needs such as pregnancy and lactation and nature of physical activity.

While designing the quality and quantity of a balanced diet the total calories are distributed among 3 classes of food in the following proportion:

Proximate principles of diet:

The proximate principles of diet are:

i. Carbohydrates: the energy yielding substances.

ii. Fats: yield energy and act as insulating materials.

iii. Proteins: act as building materials and bear the wear and tear of the body.

Construction of a diet-the spectrum of food:

The food is divided into four basic food groups:

Two glasses of milk or servings of cheese, cottage cheese, ice creams, or other dairy products.

Two servings of meat, fish, poultry or eggs, peas, beans or nuts.

3. Vegetable and fruit groups:

Four servings of green or yellow vegetables, tomatoes, citrus fruits.

4. Bread and cereal group:

Four servings of whole grains or fortified cereal products. There is no single perfect food that provides all nutritional needs for everyone. The 40 different required nutrients occur in very different proportions in different foods. Therefore a variety, within each group is essential.

1. Milk, egg and meat:

They provide the essential amino acids and have high nutritional values ranging from 98-100%. Butter supplies the fat soluble vitamins A, D and E.

Cereals supply vitamin B, and roughage (fibrous or cellulose material).

3. Essential fatty acids:

Prevents atherogenic disorders. Vegetables contain phytosterol which helps in reducing serum total cholesterol.

Citrus fruits like orange prevent diseases like scurvy, constipation etc. Fruits supply potas­sium required by the body to prevent diabetic coma.

Green leafy vegetables will help in the synthesis of Hb and provide some vitamins like vitamin A, folic acid, etc. Vegetables including green leafy vegetables prevent constipation by acting as roughage (cellulose materials).

Recommended dietary allowances (RDA):

The food and nutritional board of National Academy of Sciences, National Research Council has developed a table of recommended daily dietary allowances (RDA) of various nutrients for optimum nutrition of infants, children, adults, pregnant & lactating women and various conditions of health and diseases to provide an ample safety margin of life.

Formulation of a diet:

A correct diet must provide for maintenance of the body as well as energy requirements, for growth and reproduction. The essential elements lost by the body by excretion must be replaced.

The important factors are:

The average caloric requirement of an adult male and female should be met by the food provided daily.

2. Quality and quantity of the constituents of food:

(a) Primary foods (proteins, fats and carbohydrates):

Proteins, fats and carbohydrates are con­sumed in the ratio of 1: 1: 4. 3000 calories are provided by 100 grams of protein, 100 grams of fat and 400 grams of carbohydrates. It is advisable that 10-15% of the total calories should be obtained from protein, 20-30% from fat and 50-70% from carbohydrate.

(b) Secondary foods (vitamins and minerals):

These are essential in the diet but in very minute quantities to enable utilization of primary foods.

Although water is not a food, it is ordinarily consumed in the diet and serves a prime role in the health of the body. Hence it is one of the components of food.

3. Variation in the diet:

There is a risk of missing some essential elements or vitamins in a varied diet. Eskimos live mainly on fish and meat and poor Orientals chiefly live on rice with small amounts of fish and meat.

4. Digestibility of the food:

The food is of no use if it is not digested in the alimentary canal. Digestibility is more concerned with absorbability. When fats and starch are largely used, vege­tables and animal proteins are not absorbed. Absorption is enhanced with a mixed diet than when the substance is taken alone.

Food consistency is considerably changed on cooking. Harmful organisms are destroyed. Cooking breaks down the connective tissue fibres of meat and makes meat easier to masticate and helps in digestion. Overcooking shrinks the coagulated protein and decreases the digestibility.

Cooking increases the water content and digestibility of vegetables. Cellulose frame work is loosened and starch from starch grains is liberated. Fats are not changed much upon cooking. Cooking enhances the flavour of the food. However, vitamins B and C are destroyed when vegetables are cooked.

6. Psychological factors:

Appetite is reduced by worry and anxiety. Digestion is also upset due to imperfect mastication and secretion of digestive juices. Consumption of food is increased while taken in pleasant surroundings and good company with different items.

Dietary food is much influenced by family income. When the income is good, consumption is high with all the protective foods. A poor income has poor protective foods. Lowest income group having low protective foods suffer form rickets and nutritional anemia. They are less resistant to infectious diseases.

Relationship between Diet and Mental Health in a Young Adult Appalachian College Population

Young adults in Appalachia may face poor nutritional status due to low access to healthy food and high mental health symptoms attributed to high stress and the college environment. A cross-sectional design was used to investigate the relationship between diet intake and mental health status of this population via surveys. Participant responses (n = 1956) showed students' mean number of depressed days over the past 30 days was 9.67 ± 8.80, and of anxious days, 14.1 ± 10.03. The mean fruit and vegetable intake was 1.80 ± 1.27 times per day and the mean added sugars intake was 1.79 ± 1.26 times per day. 36.7% of students were found to be food insecure. One-way ANOVA and Chi-Squared analyses were used to determine relationship between variables. Significant variables were placed into a full logistic regression model. Food insecurity and fruit and vegetable intake remained significant predictors of depression in males (odds ratio (OR) = 2.33 95% CI 1.47⁻3.71 and OR = 68 95% CI 50⁻89, respectively) and in females food insecurity remained a significant predictor of depression (OR = 2.26 95% CI 1.67⁻3.07). Food insecurity and added sugars intake were significant predictor of anxiety in males (OR = 2.33 95% CI 1.47⁻3.71 and OR = 1.09 95% CI 0.91⁻1.3, respectively) and for anxiety in females, added sugars intake and food insecurity were significant predictors (OR = 1.18 95% CI 1.05⁻1.32 and OR = 1.65 95% CI 1.27⁻2.16, respectively). Improving college student's diet intake through increased access to healthy foods could improve the mental health and well-being of students.

Keywords: college diet quality food insecurity mental health student young adult.

10.8: Nutrition and Diet - Biology

Why is nutrition important for kids?

Eating good foods is especially important for kids because they are still growing. Kids' bodies need nutrition to grow strong healthy bones and muscles. If you don't get all the vitamins and minerals you need while you are growing, you won't grow as tall and as strong as you could be.

  • Grains - breads, cereal, pasta, rice
  • Dairy - milk, cheese, yogurt
  • Fruits - apples, oranges, berries, grapes, bananas
  • Vegetables - broccoli, beans, spinach, carrots, peas
  • Protein - beef, chicken, pork, eggs, nuts, fish

The United States Department of Agriculture (USDA) has come up with a picture of a plate to help us to make sure we get all the nutrients we need each meal. Here is the picture:

As you can see, each of the five food groups is drawn on the plate. Notice that the vegetables and grains portions are slightly larger than the fruit and protein portions. This gives you an idea of what foods you need to eat and how much of each.

  • Drink skim milk or low fat milk.
  • Eat whole grains for your grains. One example is wheat bread instead of white bread.
  • Drink water instead of sugary drinks.

Calories are a measure of how much energy is in food. When we eat, we gain calories and it gives us energy to run around and do stuff. If we eat more calories than we use moving around, then our body stores up the calories in fat. If we use more calories than we eat, then our body will start to burn up fat that was stored earlier.

Nutrition and Diet: Food Science Experiments

One of the first places to start learning more about nutrition is to take a look at your own diet. You may not think much about what you eat in a typical day, but the foods you choose are very important for your overall health. The food pyramid shows the various food groups and the number of servings people should have from these groups. The groups include grains, vegetables, fruits, dairy, proteins, and fats. At the base of the pyramid, grains should make up the biggest part of people’s diets. Fruits and vegetables come next, dairy and proteins above this, and fats sit at the top of the pyramid. You could keep a food journal for several days to learn about your typical diet. Once you know what you tend to eat, compare it to the food pyramid to see if you might need to make some adjustments. Getting your whole family involved with following the food pyramid can help everyone feel more healthy.

Conducting nutrition science experiments is another way to learn about diet and nutrition. Food experiments are easily conducted in your kitchen, often using materials you already have on hand. An experiment about tasting helps you learn about the science behind tasting, your tongue, and taste buds. The experiment involves examining the tongues of several participants, counting the number of papillae, or taste buds, within a small area of the tongue. The number of papillae corresponds with tasting abilities, with people being non-tasters, average tasters, or super-tasters.

Another popular experiment to try involves diet soda and mint candies. Set the experiment up outside so you don’t make a mess in the kitchen! Simply open a bottle of diet soda, add the mint candies, and watch the liquid explode. The liquid explodes because the candies cause a huge release of carbon dioxide, which is already present in the drink. You could also use soda to learn about the corrosiveness of this liquid. Pour a small amount of soda into a plastic cup, and place a tarnished penny in the liquid. Watch the penny every day for about one week to see what happens to it. As the penny’s tarnish is slowly removed by the soda, you can think about the corrosive properties of soda and what it might do to a person’s digestive tract.

Participating in a science fair is a great way to learn about nutrition. To choose a project, consider a question you might have about nutrition or food. For example, you might wonder about the differences between fresh and frozen food and which tastes better. To answer these questions, collect samples of foods such as fruits, vegetables, and meats. Divide the foods into two groups, and keep one group fresh while you freeze the other group. After freezing, examine both the fresh and frozen foods under a microscope and record your results. Then, prepare both foods using the same process. Perform a taste test on both foods using a group of volunteers, and record preference results. Analyze your data to determine whether volunteers preferred the fresh or frozen foods. You could also explore the permeability of different brands of plastic wrap to determine how quickly different brands allow moisture in food to get through the plastic wrap. This project involves setting up identical bowls of food and covering each bowl with a different brand of plastic wrap. Weigh each bowl at the beginning of the project and record the weights. Leave the bowls on the counter for a week, and then weigh each one at the end of the week. The bowl that is the closest to its original weight experienced the least amount of evaporation, or water permeating the plastic wrap.

Visit the following websites to learn more about science experiments and science fair project ideas:


A healthy diet can improve and maintain optimal health. In developed countries, affluence enables unconstrained caloric intake and possibly inappropriate food choices. [2]

Health agencies recommend that people maintain a normal weight by limiting consumption of energy-dense foods and sugary drinks, eating plant-based food, limiting consumption of red and processed meat, and limiting alcohol intake. [3]

The Dietary Guidelines for Americans is an evidence-based information source that policy makers and health professionals use to advise the general public about healthy nutrition.

Many do not eat food from animal sources to varying degrees (e.g. flexitarianism, pescetarianism, vegetarianism, veganism) for health reasons, issues surrounding morality, or to reduce their personal impact on the environment, although some [ which? ] of the public assumptions about which diets have lower impacts are known to be incorrect. [4] [ needs update ] Out of the above diets, veganism is the most selective. [5] People on a balanced vegan diet can get all necessary nutrients, but may need to specifically focus on consumption of nutrients like protein, iron, calcium, zinc, and vitamin B12. [6]

Raw foodism is another contemporary trend.

A particular diet may be chosen to promote weight loss or weight gain. Changing a subject's dietary intake, or "going on a diet", can change the energy balance and increase or decrease the amount of fat stored by the body. The terms "healthy diet" and "diet for weight management"(dieting) are often related, as the two promote healthy weight management. [7] [8] If a person is overweight or obese, changing to a diet and lifestyle that allows them to burn more calories than they consume may improve their overall health, possibly preventing diseases that are attributed in part to weight, including heart disease and diabetes. [9] Conversely, if a person is underweight due to illness or malnutrition, they may change their diet to promote weight gain. Intentional changes in weight, though often beneficial, can be potentially harmful to the body if they occur too rapidly. Unintentional rapid weight change can be caused by the body's reaction to some medications, or may be a sign of major medical problems including thyroid issues and cancer among other diseases. [10]

Eating disorders Edit

An eating disorder is a mental disorder that interferes with normal food consumption. It is defined by abnormal eating habits and thoughts about food that may involve eating much more or much less than needed. [11] Common eating disorders include anorexia nervosa, bulimia nervosa, and binge-eating disorder. [12] Eating disorders affect people of every gender, age, socioeconomic status, and body size. [12]

Some cultures and religions have restrictions concerning what foods are acceptable in their diet. For example, only Kosher foods are permitted in Judaism, and Halal foods in Islam. Although Buddhists are generally vegetarians, the practice varies and meat-eating may be permitted depending on the sects. [13] In Hinduism, vegetarianism is the ideal. Jains are strictly vegetarian and in addition to that the consumption of any roots (ex: potatoes, carrots) is not permitted.

10.8: Nutrition and Diet - Biology

This jet engine burns fuel. You don’t.

The dominant paradigm of weight management is (calories in) – (calories out)= (weight gain or loss). Supposedly, if you eat more calories than you “burn,” you gain weight because the calories don’t have anywhere to go but into your fat cells. This makes people sound like machines that burn fuel. We aren’t machines. We’re much more complicated and interesting.

A diet in which you consume less than 50-100 grams of carbohydrates (sugars) per day + over 60% of your calories from healthy fats + sufficient protein + fiber + essential nutrients results in the healthiest human beings. That’s probably very different from what you’ve been told is a healthy diet. For most people, that diet should cause their body to flip to nutritional ketosis, using ketones for normal metabolism instead of glucose. On this site, we’ll explore what has been learned in recent years regarding the biological basis of healthy nutrition. We’ll also think about how to avoid the sugars that are truly toxic to your health.

Here’s the “equation” for disease– a diet of mostly carbohydrates in which more than 10% of the calories come from sugars (table sugar, high fructose corn, syrup, fruit juices, etc) or easily digested carbohydrates, which become sugars, will cause obesity, diabetes, heart disease, Alzheimer’s, cancers, food allergies, and interfere with young children’s nervous system development. There are a cascade of possible metabolically induced disease conditions. Your exact genetic makeup will determine which problems you’re most prone to when you eat a high carbohydrate, inflammatory diet. In my family, one area of weakness is the eyes.

The reason the (calories eaten) – (calories burned) = (weight gain or loss) equation doesn’t work is because your body doesn’t handle sugars, fats, and proteins the same way. I talk about sugar a lot because the carbohydrates (“carbs”) you see listed on food labels and in weight loss articles are made of sugar molecules stuck together. To digest carbohydrates, your digestive tract breaks them down into individual sugar molecules and absorbs those into your bloodstream. The complicated biochemical paths that use sugars, fats, and proteins are separate and different. They are used differently and have different effects on your body. They trigger different hormonal regulatory mechanisms as well. Only glucose sugar triggers elevated insulin, for example.

It also matters that for millions of years, the type of foods humans and their ancestors ate drove the evolution of the metabolic paths in our body that used the food. Herbivores eat plants with more carbohydrates and fiber, usually with way less fat and protein, unless the herbivore is a nut-eater. Carnivores eat other animals, getting most of their calories from fats and proteins. Our lineage of hominids were omnivores that became predators, eating meat preferentially, although we could still survive on other foods. We could get a little fatter in fruit and berry season, since the only way to store the energy from the sugars in the fruits and berries is as fat. As I’ll discuss in the Biology section, for at least 1.8 million years, we were the most effective predators the planet has ever seen. We’ve only been growing plants as food for a few thousand years. We’ve only been eating refined sugars, most of the common vegetable oils, and processed foods for a couple of centuries or so, unless you were a rich person with access to high sugar foods. When you eat foods evolution didn’t prepare you for, your brain and body gets confused and sick. Conversely, if you eat foods you’re well adapted to everything works better. The damage caused by long term inflammation starts to repair, at least in part.

Browse the site to explore different topics. Go to the How-To section if you want specific diet and exercise suggestions.

If you’d like a quick, very entertaining introduction to many of the key concepts on this site, watch That Sugar Film, which I review here.

KS3 Unit 8A Biology Diet and digestion WORKSHEETS ONLY (Nutrients, Balanced diets, Absorption)

After a PhD in Medicinal Chemistry and some time in industry I finally found my calling as a secondary school teacher in Chemistry. Enjoy! Please review the resources you buy in order for me to improve my teaching and my lessons

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KS3 Scheme of work and lessons for Unit 8A Biology: Diet and digestion

Aimed for mid-high ability but can be adapted for low ability

8Aa Nutrients:
Lesson 1- Food labelling
Lesson 2 - Food tests
8Ac Balanced diets:
Lesson 3 - Balanced diets and Malnutrition/Obesity
Lesson 4 - Deficiency diseases
8Ad Digestion:
Lesson 5 - Digestive system
Lesson 6 - Digestive enzymes
8Ae Absorption:
Lesson 7 - Small intestine and absorption
Lesson 8 - Diffusion

7 lessons including practicals (8Ae Absorption - could be split into two lessons)

All extension questions available on each slide
Answers all underneath each slide
Support also available where necessary
AfL sections and mini quizzes
Reducing the need for photocopying


All relating to specification (any pictures used have all been taken from the internet and I am not trying to claim rights to any pictures or information used)


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Diet and Nutrition

Living with inflammatory bowel disease (IBD) means paying special attention to what you eat. Eating certain foods can help ease your symptoms, while other things you like to eat may make your symptoms worse.

Restoring and maintaining good nutrition is a balancing act. Your diet needs to include enough calories and and nutrients to keep you healthy so you are not at risk of becoming malnourished.

The best way to maintain adequate nutrition is to work with your healthcare team, make healthy food choices, and avoid foods that make your symptoms worse. We can help you stay on the right track with information and resources about the relationship of nutrition and IBD.

To learn more about how diet and nutrition can impact IBD, and to find key recommendations on how to maintain good nutrition, watch IBD: Diet and Nutrition

NEW - View our recent June MyIBDLearning webinar series to learn about diet and nutrition in IBD and how your relationship with food can impact your mental health.

Watch the video: Nutrition and Diet - GCSE Biology 9-1 (May 2022).