Can you eat more calories than the body can store?

Can you eat more calories than the body can store?

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I believe I have read that if the body takes in too many certain nutrients/vitamins, the body simply excretes them.

How does this behave with calories? If I have a daily consumption of exactly 2,000 calories, would the body gain more weight if I took 6,000 calories in one day or if I took 2,500 calories over 8 days?

I know that excess calories can be stored by the body, but is there a point where the body can't keep up and excrete the rest?

As @John already pointed out, efficiency of digestion can be assumed to decrease in case of extreme uptake of excessive calories. (diarrhea)

In terms of the excretory system: Proteins are generally strongly retained by the kidneys, while glucose famously could leave the body through urine (diabetes) but should be taken up by your cells under normal circumstances. Fats, as carried by transporter proteins, should not be excreeted either. So I don't think you would excrete many calories.

Also I remember some papers stating, that short-term excessive caloric uptake is correlated with down-regulation of glucose transporters to your brain, while prolonged uptake of excessive calories (more than around 3-7 days) leads to changes in the brain-barriers permeability properties. It was observed that this change in permeability has long-term fatalistic effects: It will cause hippocampal damage and in turn further cause high caloric intake as a behavioral change due to reduced internal cues that depend on the hippocampus.

Calories: How to Know if You Go Too Low

Eating too few calories may actually hamper your weight-loss goals. Here's how to tell if your calorie counting is counterproductive.

Cutting calories is the approach most dieters must take to meet their weight-loss goals. But every once in a while people take calorie restriction too far, ultimately making weight loss slower and more difficult by slowing your metabolism.

Figuring out the right number of calories for you on a daily basis depends on your age, gender, and activity level. In general, the younger and more active you are, the more calories you can consume. And men are able to eat more calories daily than women. For example, the U.S. Department of Agriculture guidelines says that women 19 to 30 years old should consume 2,000 calories if they have a sedentary lifestyle or 2,400 calories if they have an active one for men of the same age the range is 2,400 to 3,000 calories.

Defining the Low-Calorie Diet

It seems logical that if calories are the problem, you would want to eat as few of them as possible to speed weight loss. As a general rule, people need a minimum of 1,200 calories daily to stay healthy. People who have a strenuous fitness routine or perform many daily activities need more calories. If you have reduced your calorie intake below 1,200 calories a day, you could be hurting your body in addition to your weight-loss plans.

“The big picture is to consume enough calories with a balance of nutrients and engage in physical activity for good health management to achieve one’s weight goals. Consuming less than 1,200 calories per day may make it difficult to meet vitamin and mineral needs via food,” says nutrition therapist Andrea Spivack, MA, RD, LDN, with Penn Behavioral Health at the University of Pennsylvania in Philadelphia.

Tempting as it may be to continue with your low-calorie weight-loss plan and simply take a supplement, Spivack points out that there are some key nutrients which are only available through your diet.

Occasionally, obese people will go on a very low-calorie diet — 800 to 1,000 calories per day — for a brief period of time in order to achieve a specific weight-loss goal, but then will switch to a diet with more calories to reach and maintain their desired weight. Such a diet is usually supervised by a doctor or nutritionist so that it is nutritionally balanced. Unfortunately, weight regain is common after these restricted calorie diets end.

Why Low-Calorie Diets Slow Your Metabolism

If you are on a very low-calorie diet, you may wonder why the numbers on your scale aren’t budging, but your diet buddy is slimmer by the month.

The reality is that different people respond differently to low-calorie diets. When your body senses that food may not be in plentiful supply, it may slow down your metabolism as protection against the possibility of starvation, even if you are obese and deliberately trying to lose weight.

“In some people, the metabolic rate [how fast the body burns calories] is only slightly reduced to make up the shortfall in energy difference, while in others it is far greater. It is this variability in the metabolic rate with energy restriction that causes much of the variability in weight loss between people,” explains Leanne M. Redman, PhD, an instructor of human physiology at the Pennington Biomedical Research Center in Baton Rouge, La. Redman and colleagues have been studying the impact of very low-calorie diets on weight loss and other measures of health.

Calories: Are You Getting Enough?

Here are signs that you are not getting enough calories:

  • You are having a hard time sticking to your diet plan. It's hard to stick to extremely low-calorie diets, which can hurt your long-term success. Boredom and hunger can both undermine your weight-loss goals.
  • Your weight loss is stalling. A study of 48 overweight people compared the results of a calorie restriction diet, diet and exercise, and a normal diet over six months and found that many of those eating the lower amount of calories had increasingly slow metabolisms as time went by. This translates into slowed weight loss.

You can use online tools, such as My Calorie Counter, to help you track your daily calorie intake. MCC allows you to set a target for daily calorie consumption and can tell you throughout the day how you are doing.

If you are still interested in a low-calorie diet, consult a doctor or dietitian who can help you create a nutritionally balanced diet that won’t leave you hungry and frustrated.

Exams and Tests

The health care provider will perform a physical exam and ask about your medical history, eating habits, and exercise routine.

The two most common ways to assess your weight and measure health risks related to your weight are:

BMI is calculated using height and weight. You and your provider can use your BMI to estimate how much body fat you have.

Your waist measurement is another way to estimate how much body fat you have. Extra weight around your middle or stomach area increases your risk for type 2 diabetes, heart disease, and stroke. People with "apple-shaped" bodies (meaning they tend to store fat around their waist and have a slim lower body) also have an increased risk for these diseases.

Skin fold measurements may be taken to check your body fat percentage.

Blood tests may be done to look for thyroid or hormone problems that could lead to weight gain.

What time of day do we burn the most calories?

A recent study shows that a person’s metabolism does not stay the same for 24 hours — in fact, there are times of the day where their body is chewing through a greater number of calories while they are just sitting there.

Share on Pinterest According to a new study, a person’s energy-burning ability fluctuates across the day.

The research, published in Current Biology, shows that our body’s internal clock may have more to do with how we process calories than previously thought.

While sitting around in the late afternoon and early evening may not feel that much different from sitting around in the morning, a person burns 10 percent more calories later in the day.

Everyone burns calories no matter what they are doing, even while they are taking a nap.

The human body needs calories and uses them to supply the body with the energy it requires to function properly.

To find out a little more about our internal calorie-burning capabilities, the researchers carried out a study on seven people. The participants stayed in an isolated laboratory setting that had no windows, clocks, phones, or Internet. This meant they had no clues as to what time of day it was.

Each person was assigned a time to go to bed, and a time to wake up, and throughout the 3-week study, those times were adjusted 4 hours later each day. Essentially, this was comparable with “circling the globe every week.”

Since their bodies were not able to settle into a rhythm because they were sleeping and waking at different times every day, they developed their own patterns. The researchers measured their metabolic rate at different times of the day to determine how their bodies dealt with calorie consumption all around the clock.

They discovered that metabolic rate was lowest late during their biological “night,” and highest around 12 hours later, in the biological “afternoon and evening.”

“The fact that doing the same thing at one time of day burned so many more calories than doing the same thing at a different time of day surprised us,” says lead author Kirsi-Marja Zitting of the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School, both in Boston, MA.

Humans burn calories no matter what they do, whether they are sleeping in a bed, walking around the block, or running a marathon.

People take in calories through food and drink and use those calories up by breathing, digesting foods, and with every movement they make. The more a person moves, the more calories they burn .

People often turn to calorie-counting when they are hoping to lose some weight because when a person burns more calories than they take in, they tend to lose weight.

Everyone has their own personal resting metabolic rate, which is a measure of how quickly the body uses up energy. The study revealed that this rate fluctuates throughout the day.

If our bodies burn calories a little faster in the afternoon to early evening, it might be a good idea to make lunch the biggest meal of the day instead of dinner.

Jeanne Duffy, also in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital, says:

“It is not only what we eat, but when we eat — and rest — that impacts how much energy we burn or store as fat. Regularity of habits, such as eating and sleeping, is very important to overall health.”

This team plans to study how appetite and the body’s response to food differ depending on the time of day. They also want to investigate how sleep — how long and how often a person sleeps — affects their body’s response to food.

This Is The Best Time To Eat If You Want To Burn More Calories

You tend to burn more calories late afternoon or early evening


  • You are likely to burn more calories in the afternoon
  • Your eating schedule should be according to your lifestyle
  • Eat your breakfast withing 30 minutes of waking up

If a recent study is to be believed, afternoon is the time when more calories are burned than any other time of the day. Researchers have found that 10% more calories are burned in late afternoon or early evening. Published in journal of Current Biology, the study found that 10% more calories are burned at rest in late afternoon and early evening as compared to early morning hours. The study helped in explaining why irregular eating and sleeping schedules can cause weight gain in people. Findings of the study also showed that resting energy is expenditure is lowest at the circadian phase in the late biological night and highest about 12 hours later in biological afternoon or evening.

Thus, apart from what to eat, attention needs to be paid to what time you are eating and the rest which impacts how much energy you burn or store as fat.

A few studies done previously have talked about how eating your meals at specific time of the day can help you lose weight. Timing of meal can affect body-weight regulation, management of obesity related diseases, sleep cycle and even metabolic regulation.

It has been found that interfering with sleep and body's internal clock can make you eat at wrong times and cause weight gain. Late night owls are more likely to eat their meals at wrong time, and this can lead to an increase in weight.

Timing of meal can influence your weight loss goals
Photo Credit: iStock

The ideal time to eat meals is the one which suits your lifestyle. Under usual circumstances, you should make the effort to eat your breakfast within 30 minutes of waking up. Try keeping a gap of at least 4 hours between your breakfast and lunch. Dinner should ideally be consumed 2 to 3 hours before your bedtime.

For those who are struggling to lose weight, changing time of meals according to the aforementioned plan can be helpful. Agrees Delhi-based nutritionist Pooja Malhotra who also says that breakfast should be eaten within 30 minutes of waking up. She tells DoctorNDTV that your breakfast should be a wholesome and balanced meal including all food groups.

In case a person has a schedule which doesn't allow eating breakfast within 30 minutes of waking up, they can have a fruit along with some nuts and milk, and then have a wholesome breakfast within the next hour.

(Pooja Malhotra is a nutritionist based in Delhi)

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.

A pound of fat contains about 3,500 calories. Therefore, most people will lose about 1 pound of body fat for every 3,500-calorie deficit they create. When you eat 500 fewer calories than you need for energy each day, you'll lose about 1 pound per week. To customize this formula, multiply your weight in pounds by 15 to estimate your daily energy needs. This assumes that you are moderately active, which you should be if you're trying to lose weight. For example, a moderately active 145-pound person burns about 2,175 calories per day and will burn 1 pound of fat per week eating 1,675 calories per day.

While it may seem logical that cutting more calories will lead to greater fat loss, this isn't always the case. When you create too large a calorie deficit, your body tends to burn more muscle than fat. Calorie deprivation also slows your metabolism -- the rate at which you burn calories -- because your body tries to conserve energy when it feels starved. To avoid such nutritional deprivation, Harvard Health Publications recommends that women eat at least 1,200 calories a day and men eat at least 1,500 calories per day.

The Truth About Your Body Going Into 'Starvation Mode'

If a list of nutritional urban legends existed, the idea that your body can easily slip into starvation mode would be high up there. Drilling down a bit, I'm specifically talking about the often-repeated belief that if you limit your caloric intake (or even fast) for a day or several days, your metabolism is going to take a hit because your body goes into so-called "starvation mode" and does everything it can to preserve energy.

Here's the deal: When you read or hear about this concept, it's usually because someone is trying to explain why dramatically cutting calories to lose weight is a bad idea. The starvation mode theory holds that crash-dieting isn't just dangerous, but it's also counterproductive. You're trying to lose weight, but you're actually slowing down your metabolism, which makes it even harder to accomplish your goals! Unfortunately, the idea that crash-dieting will slow your metabolism, while well intentioned, isn't really an accurate read of the science. I'll talk about why in more detail. But also, something else I'm going to talk about: Crash-dieting or yo-yo dieting or dramatically cutting calories for the sake of weight loss is definitely still a bad idea, and also counterproductive. Just…not because of the metabolism thing. Let's get into it.

The concept of starvation mode is confusing because, yes, it is a thing—if you don’t eat enough, in response to the low intake of fuel, your body will likely store calories it would otherwise burn. But starvation mode isn’t an ever-present threat lurking around every corner, just waiting for you to skip a meal so it can kick into gear and mess with your metabolism.

“A lot of times people think they’re going into starvation mode when they skip a meal or fast for a day, and that’s truly not the case,” Philadelphia-based Joy Dubost, Ph.D., R.D., tells SELF. Unless someone has a prolonged, dire lack of access to food or an eating disorder like anorexia, it’s very hard to go into what Dubost describes as “complete clinical starvation mode.”

Rachele Pojednic, Ph.D., assistant professor in the nutrition department at Simmons College and staff scientist at Beth Israel Deaconess Medical Center, agrees. “There’s a difference between the popular perception of starvation mode with regard to diet culture and actually being starving,” she tells SELF.

When a person has been eating a low-calorie diet for long enough to actually be starving—there’s no specific caloric threshold or length of time for this to happen because it’s so individual, the experts explain, but it certainly takes longer than a day without food—a few physiological processes take place.

For starters, your insulin and glucose levels can get thrown out of whack. Insulin is a hormone that shuttles glucose (blood sugar) from the bloodstream into the body's cells, where's it's stored as glycogen for later use as energy. When insulin is low, that keeps the glucose in your blood. This happens in the case of starvation so that you have more blood glucose available for quick energy, Pojednic explains. Your body will also start to increase a process known as lipolysis, or breaking down fat to release fatty acids for energy. In addition, you’ll break down protein reserves, usually muscle, for another energy source, Dubost explains, and undergo large mineral losses that affect your body’s electrical systems, like your heart. Symptoms of all of this can include weakness, apathy, memory lapses, and muscle cramps.

“It’s really hard, if you have adequate access to food, to put yourself into this mode because you are always going to be able to eat something eventually,” Pojednic says.

Experts tend to recommend eating every three to four hours for optimal energy and health. Starvation mode happens over the long-term, so skipping a meal every once in a while won't permanently affect your metabolism. Haphazardly skipping meals can still affect your weight in another way, however.

“The tendency on the other end of [skipping meals] is to overcompensate,” Pojednic says. “You’re not going to go and eat a well-balanced healthy meal—you’re probably going to go eat something that’s not particularly good for you, or it’s a massive portion.” It can also make you hangry, which is bad news.

Fascinatingly enough, some research shows that skipping meals in the form of intermittent fasting (IF) a structured method of alternating days of eating less (or nothing) with days of eating normally or having whatever you want, might be beneficial for health and weight loss. “There's interesting emerging science on intermittent fasting and calorie restriction,” Pojednic says.

The research is limited, but when done properly, intermittent fasting looks promising for weight loss. For example, a 2015 review in Molecular and Cellular Endocrinology analyzed 40 studies of intermittent fasting and found that people lost 7 to 11 pounds over 10 weeks of IF. Many of the studies involved fasting periods between one and seven days, but it's worth noting that most people who practice IF alternate days of fasting with days of eating, or fast one or two days a week and eat regularly the rest of the time.

Depending on the length of a fast, it can be severe enough to cause starvation mode. But the theory is that either way, people who do intermittent fasting still end up eating fewer calories overall, thus avoiding weight gain.

That doesn't mean you should structure an intermittent fasting plan for yourself—if you're interested in trying this out, it's best to talk to a doctor or registered dietitian first. (And if you have an eating disorder, you should always check with your doctor before changing your eating habits.)

Yo-yo dieting involves repeatedly gaining and losing weight, usually due to going on and off of intense diets. In the long-term, this practice, or just consistently eating too few calories for your body can mess with your metabolism. “I see people trying to take their calorie intake down below 1,000 calories per day, and this can be very harmful to their metabolism, as well as their health overall,” Pojednic says.

When you lose a lot of weight, your metabolism automatically slows down because your body needs less energy to function. When you start eating normally again (or overeating), you’re working with a lower metabolism, which can lead to weight gain, especially if you passed your own personal starvation mode threshold and your body now wants to get as much energy as possible. “Your body is trying to conserve whatever it can,” Dubost says. This process only intensifies as you get older and your metabolism naturally slows, she adds.

There’s no easy way to determine what level of yo-yo dieting or calorie restriction will result in metabolic changes, Dubost says—it all depends on your individual body. However, experts generally recommend that women don’t eat fewer than 1,200 calories a day to avoid under eating. And if you're very active, you may need hundreds more calories than that to prevent under eating, although that varies widely depending on your activity level.

Yo-yo dieting or otherwise severely restricting calories are both bad ideas in general, not just because they can mess with your metabolism. Depriving yourself of food is taxing on your body, and over the long term, it can raise your risk of having problems with blood pressure, cholesterol, and diabetes, among other health issues. It will also likely lead to binges, because it just isn't sustainable. Instead, if you're trying to change any eating habits you may have, making small lifestyle tweaks that you can actually stick to is the best way to go about it. That way, you avoid the awful feelings that can come with forcing yourself to eat less than you need: crankiness, unhappiness, and straight up misery. There's no need to treat yourself that way!

Paying attention to your hunger cues is key. “It’s not only about eating when you are feeling that urge,” Pojednic says. “The flip side is paying attention to when you’re full and eating only enough until you feel like you’ve been satiated.”

Given our easy access to delicious food, this can be easier said than done. Mindful eating can help. So can eating high-fiber foods like whole grains, fruits, and vegetables, along with foods rich in protein and healthy fats—all of these will help fill you up and boost your health.

When it comes to being active, strength training is a great way to build muscle, which is more metabolically active than fat, meaning that adding muscle mass can help keep your metabolism high. If you don't have much muscle, your body doesn't require as much energy to function, so your metabolism doesn't need to work as hard. But it's not just about strength training. Being active in general is extremely important for your health, so it's important to find a workout method you love, Dubost says.

You May Also Like: 12 Healthy Foods You Should Always Keep in Your Pantry

Can you eat more calories than the body can store? - Biology

In 1924, Nicolas Clement first defined a calorie as a unit of heat. A calorie is then, in simplest terms, a unit of energy. In more specific terms, a calorie is the amount of energy, or heat, that it takes to raise the temperature of one gram of water one degree celsius (1.8 degrees Fahrenheit) at one atmosphere pressure. A common unit of energy used in the physical sciences is a "joule." One calorie is equal to 4.184 joules.

Although we tend to associate calories with discussions of food, they can actually apply to any substance containing energy. As an example, one gallon of gasoline (approximately 4 liters), contains about 31,000,000 calories. That's right, 31 million! In today's world, though, the use of the word "calorie" is considered obsolete when referring to anything but food energy. All other heat measurements, as in the gasoline example used above, are more correctly noted in joules.

As we know, human beings require energy to live. They need energy to breathe, energy to pump blood through their bodies, energy to walk, to dance, to run. Essentially, life is energy, and this energy is acquired from food.

Calorie vs. Kilocalorie
What most people don't realize is that the calories we refer to when studying a food label aren't truly calories. They are actually kilocalories. A kilocalorie is equal to 1,000 of the calories discussed above. So, for example, if an banana is said to have 80 calories, in actuality it has 80 kilocalories, or 80,000 'true' calories. At one time, food calories were denoted with a capital 'C' to denote kilocalories. This practice is no longer universally followed, however.

A calorie is also a measure of how much energy the body uses when it performs any activity. Like food calories, these calories are also actually kilocalories. So, when you read that you will expend 100 calories by walking around the block, in truth you are expending 100 kilocalories - or 10,000 calories.

For the purposes of the remainder of this article, whenever "calorie" is mentioned, it will be a reference to kilocalorie.

How Are Calories Calculated?
As we learned earlier, the number of calories in any food is measured by how much potential energy is in that food. Scientists have determined that one gram of a carbohydrate contains 4 calories, one gram of a protein contains 4 calories, and one gram of a fat contains 9 calories. As a result, if you know how many proteins, carbohydrates and fats any foodstuff contains, you can calculate how many calories are contained in that food. You can experiment with these calculations by looking at any food label that breaks down these food components.

How Does Your Body Use Calories?
When we eat food, our bodies "burn", or release the energy from, these calories through a system of various metabolic processes. Different food components are broken down into different materials. For example, carbohydrates are broken down into glucose and other sugars. Fats are broken down into fatty acids and glycerol. Proteins are broken down into various amino acids.

Once food is broken down into its basic component molecules, these molecules travel through the bloodstream to the individual cells. Once in the cells, the energy is available for the body to use. If you take in more calories than your body needs to exist, the excess energy will be stored by your body and you will gain weight. If you accumulate and store 3,500 extra calories you will gain one pound of fat, which is how your body stores excess energy. If you burn 3,500 more calories than you eat, your body will convert 3,500 calories of stored energy, and you will lose one pound of fat.

Does Calorie "Type" Matter?
For the sole purpose of weight gain or loss, the simple truth is that it does not matter whether the calories you consume come from carbohydrates, proteins or fats. A calorie is a calorie regardless of its origin. You will always gain weight if you consume more calories than you burn, or lose weight if you burn more calories than you take in.

It should be noted, however, that your body needs certain nutrients in order to perform at its optimum level and for you to remain healthy. It is for this purpose that scientists recommend that you eat or avoid certain foodstuffs.

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Does carbohydrate become body fat?

Ah, poor carbohydrates, maligned by diets such as Atkins’ and the ketogenic diet. However, carbohydrates are your body’s main source of energy — in fact your muscles and brain cells prefer carbs more than other sources of energy (triglycerides and fat, for example). To answer your question: research completed over the last several decades suggests that if you are eating a diet that is appropriate for your levels of daily activity, little to no carbohydrate is converted to fat in your body. For most people (unless you have a metabolic disorder) when you eat carbs they are digested, broken down to glucose, and then transported to all the cells in your body. They are then metabolized and used to support cellular processes. If you’re active and eating appropriately for your activity level, most of the carbs you consume are more or less burned immediately.

There are two caveats here: first, if you’re eating a lot more calories per day than you are burning, then yes, your liver will convert excess calories from carbohydrate into fats second, not all carbs are created equal. If you consume too many calories from simple sugars like sucrose and fructose (think sugary sodas sweetened by sugar and high fructose corn syrup) then your body will more readily take some of those sugars and turn them into triglycerides (fat) in your liver.

What happens to excess calories that come from carbs? The answer depends on several things: what kind of carbs you consumed, your genetics, as well as how many extra calories we’re talking about. For those who eat a well-balanced diet and have no metabolic disorders, excess dietary carbohydrates are converted by the liver into complex chains of glucose called glycogen. Glycogen is stored in liver and muscle cells and is a secondary source of energy to freely circulating blood glucose. When your body runs out of glucose in the blood stream, it will begin to break down and metabolize glycogen for energy. A body typically has blood glucose levels that can sustain all cellular processes for three to four hours — if you don’t eat in that time frame, your body will begin to break down the glycogen it has stored in order to keep you running.

Glycogen is one of the reasons why we don’t need to eat every fifteen to twenty minutes, and carbohydrates are easily converted to glycogen stores, then broken down and burned when you need more energy. If you saturate your body with an excessively high number of calories and the majority of these calories are from carbohydrates, then the excess carbs are converted into fat, or adipose tissue, for longer term storage. The process of conversion to fat occurs first in the liver and only after a significant period will your adipose tissue begin to expand.

Most dietitians recommend that about 50 percent of your daily calories come from carbohydrates, and many carbohydrate sources such as carrots, sweet potatoes, berries, and apples not only give your body and brain necessary fuel, but also deliver essential vitamins and nutrients.

So, although the media or diet companies claim that carbs are responsible for fat gain, the research doesn’t support this blanket statement. Carbs are an important foundation to a healthy and active lifestyle and can be quite nutritious!

Why people become overweight

Everyone knows some people who can eat ice cream, cake, and whatever else they want and still not gain weight. At the other extreme are people who seem to gain weight no matter how little they eat. Why? What are the causes of obesity? What allows one person to remain thin without effort but demands that another struggle to avoid gaining weight or regaining the pounds he or she has lost previously?

On a very simple level, your weight depends on the number of calories you consume, how many of those calories you store, and how many you burn up. But each of these factors is influenced by a combination of genes and environment. Both can affect your physiology (such as how fast you burn calories) as well as your behavior (the types of foods you choose to eat, for instance). The interplay between all these factors begins at the moment of your conception and continues throughout your life.

The calorie equation

The balance of calories stored and burned depends on your genetic makeup, your level of physical activity, and your resting energy expenditure (the number of calories your body burns while at rest). If you consistently burn all of the calories that you consume in the course of a day, you will maintain your weight. If you consume more energy (calories) than you expend, you will gain weight.

Excess calories are stored throughout your body as fat. Your body stores this fat within specialized fat cells (adipose tissue) — either by enlarging fat cells, which are always present in the body, or by creating more of them. If you decrease your food intake and consume fewer calories than you burn up, or if you exercise more and burn up more calories, your body will reduce some of your fat stores. When this happens, fat cells shrink, along with your waistline.

Genetic influences

To date, more than 400 different genes have been implicated in the causes of overweight or obesity, although only a handful appear to be major players. Genes contribute to the causes of obesity in many ways, by affecting appetite, satiety (the sense of fullness), metabolism, food cravings, body-fat distribution, and the tendency to use eating as a way to cope with stress.

The strength of the genetic influence on weight disorders varies quite a bit from person to person. Research suggests that for some people, genes account for just 25% of the predisposition to be overweight, while for others the genetic influence is as high as 70% to 80%. Having a rough idea of how large a role genes play in your weight may be helpful in terms of treating your weight problems.

How much of your weight depends on your genes?

Genes are probably a significant contributor to your obesity if you have most or all of the following characteristics:

  • You have been overweight for much of your life.
  • One or both of your parents or several other blood relatives are significantly overweight. If both of your parents have obesity, your likelihood of developing obesity is as high as 80%.
  • You can't lose weight even when you increase your physical activity and stick to a low-calorie diet for many months.

Genes are probably a lower contributor for you if you have most or all of the following characteristics:

  • You are strongly influenced by the availability of food.
  • You are moderately overweight, but you can lose weight when you follow a reasonable diet and exercise program.
  • You regain lost weight during the holiday season, after changing your eating or exercise habits, or at times when you experience psychological or social problems.

These circumstances suggest that you have a genetic predisposition to be heavy, but it's not so great that you can't overcome it with some effort.

At the other end of the spectrum, you can assume that your genetic predisposition to obesity is modest if your weight is normal and doesn't increase even when you regularly indulge in high-calorie foods and rarely exercise.

People with only a moderate genetic predisposition to be overweight have a good chance of losing weight on their own by eating fewer calories and getting more vigorous exercise more often. These people are more likely to be able to maintain this lower weight.

What are thrifty genes?

When the prey escaped or the crops failed, how did our ancestors survive? Those who could store body fat to live off during the lean times lived, and those who couldn't, perished. This evolutionary adaptation explains why most modern humans — about 85% of us — carry so-called thrifty genes, which help us conserve energy and store fat. Today, of course, these thrifty genes are a curse rather than a blessing. Not only is food readily available to us nearly around the clock, we don't even have to hunt or harvest it!

In contrast, people with a strong genetic predisposition to obesity may not be able to lose weight with the usual forms of diet and exercise therapy. Even if they lose weight, they are less likely to maintain the weight loss. For people with a very strong genetic predisposition, sheer willpower is ineffective in counteracting their tendency to be overweight. Typically, these people can maintain weight loss only under a doctor's guidance. They are also the most likely to require weight-loss drugs or surgery.

The prevalence of obesity among adults in the United States has been rising since the 1970s. Genes alone cannot possibly explain such a rapid rise. Although the genetic predisposition to be overweight varies widely from person to person, the rise in body mass index appears to be nearly universal, cutting across all demographic groups. These findings underscore the importance of changes in our environment that contribute to the epidemic of overweight and obesity.

Environmental causes of obesity

Genetic factors are the forces inside you that help you gain weight and stay overweight environmental factors are the outside forces that contribute to these problems. They encompass anything in our environment that makes us more likely to eat too much or exercise too little. Taken together, experts think that environmental factors are the driving force for the causes of obesity and its dramatic rise.

Environmental influences come into play very early, even before you're born. Researchers sometimes call these in-utero exposures "fetal programming." Babies of mothers who smoked during pregnancy are more likely to become overweight than those whose mothers didn't smoke. The same is true for babies born to mothers who had diabetes. Researchers believe these conditions may somehow alter the growing baby's metabolism in ways that show up later in life.

After birth, babies who are breast-fed for more than three months are less likely to have obesity as adolescents compared with infants who are breast-fed for less than three months.

Childhood habits often stick with people for the rest of their lives. Kids who drink sugary sodas and eat high-calorie, processed foods develop a taste for these products and continue eating them as adults, which tends to promote weight gain. Likewise, kids who watch television and play video games instead of being active may be programming themselves for a sedentary future.

Many features of modern life promote weight gain. In short, today's "obesogenic" environment encourages us to eat more and exercise less. And there's growing evidence that broader aspects of the way we live — such as how much we sleep, our stress levels, and other psychological factors — can affect weight as well.

The food factor as one of the causes of obesity

According to the Centers for Disease Control and Prevention (CDC), Americans are eating more calories on average than they did in the 1970s. Between 1971 and 2000, the average man added 168 calories to his daily fare, while the average woman added 335 calories a day. What's driving this trend? Experts say it's a combination of increased availability, bigger portions, and more high-calorie foods.

Practically everywhere we go — shopping centers, sports stadiums, movie theaters — food is readily available. You can buy snacks or meals at roadside rest stops, 24-hour convenience stores, even gyms and health clubs. Americans are spending far more on foods eaten out of the home: In 1970, we spent 27% of our food budget on away-from-home food by 2006, that percentage had risen to 46%.

In the 1950s, fast-food restaurants offered one portion size. Today, portion sizes have ballooned, a trend that has spilled over into many other foods, from cookies and popcorn to sandwiches and steaks. A typical serving of French fries from McDonald's contains three times more calories than when the franchise began. A single "super-sized" meal may contain 1,500–2,000 calories — all the calories that most people need for an entire day. And research shows that people will often eat what's in front of them, even if they're already full. Not surprisingly, we're also eating more high-calorie foods (especially salty snacks, soft drinks, and pizza), which are much more readily available than lower-calorie choices like salads and whole fruits. Fat isn't necessarily the problem in fact, research shows that the fat content of our diet has actually gone down since the early 1980s. But many low-fat foods are very high in calories because they contain large amounts of sugar to improve their taste and palatability. In fact, many low-fat foods are actually higher in calories than foods that are not low fat.

The exercise equation

The government's current recommendations for exercise call for an hour of moderate to vigorous exercise a day. But fewer than 25% of Americans meet that goal.

Our daily lives don't offer many opportunities for activity. Children don't exercise as much in school, often because of cutbacks in physical education classes. Many people drive to work and spend much of the day sitting at a computer terminal. Because we work long hours, we have trouble finding the time to go to the gym, play a sport, or exercise in other ways.

Instead of walking to local shops and toting shopping bags, we drive to one-stop megastores, where we park close to the entrance, wheel our purchases in a shopping cart, and drive home. The widespread use of vacuum cleaners, dishwashers, leaf blowers, and a host of other appliances takes nearly all the physical effort out of daily chores and can contribute as one of the causes of obesity.

The trouble with TV: Sedentary snacking

The average American watches about four hours of television per day, a habit that's been linked to overweight or obesity in a number of studies. Data from the National Health and Nutrition Examination Survey, a long-term study monitoring the health of American adults, revealed that people with overweight and obesity spend more time watching television and playing video games than people of normal weight. Watching television more than two hours a day also raises the risk of overweight in children, even in those as young as three years old.

Part of the problem may be that people are watching television instead of exercising or doing other activities that burn more calories (watching TV burns only slightly more calories than sleeping, and less than other sedentary pursuits such as sewing or reading). But food advertisements also may play a significant role. The average hour-long TV show features about 11 food and beverage commercials, which encourage people to eat. And studies show that eating food in front of the TV stimulates people to eat more calories, and particularly more calories from fat. In fact, a study that limited the amount of TV kids watched demonstrated that this practice helped them lose weight — but not because they became more active when they weren't watching TV. The difference was that the children ate more snacks when they were watching television than when doing other activities, even sedentary ones.

Stress and related issues

Obesity experts now believe that a number of different aspects of American society may conspire to promote weight gain. Stress is a common thread intertwining these factors. For example, these days it's commonplace to work long hours and take shorter or less frequent vacations. In many families, both parents work, which makes it harder to find time for families to shop, prepare, and eat healthy foods together. Round-the-clock TV news means we hear more frequent reports of child abductions and random violent acts. This does more than increase stress levels it also makes parents more reluctant to allow children to ride their bikes to the park to play. Parents end up driving kids to play dates and structured activities, which means less activity for the kids and more stress for parents. Time pressures — whether for school, work, or family obligations — often lead people to eat on the run and to sacrifice sleep, both of which can contribute to weight gain.

Some researchers also think that the very act of eating irregularly and on the run may be another one of the causes of obesity. Neurological evidence indicates that the brain's biological clock — the pacemaker that controls numerous other daily rhythms in our bodies — may also help to regulate hunger and satiety signals. Ideally, these signals should keep our weight steady. They should prompt us to eat when our body fat falls below a certain level or when we need more body fat (during pregnancy, for example), and they should tell us when we feel satiated and should stop eating. Close connections between the brain's pacemaker and the appetite control center in the hypothalamus suggest that hunger and satiety are affected by temporal cues. Irregular eating patterns may disrupt the effectiveness of these cues in a way that promotes obesity.

Similarly, research shows that the less you sleep, the more likely you are to gain weight. Lack of sufficient sleep tends to disrupt hormones that control hunger and appetite and could be another one of the causes of obesity. In a 2004 study of more than 1,000 volunteers, researchers found that people who slept less than eight hours a night had higher levels of body fat than those who slept more, and the people who slept the fewest hours weighed the most.

Stress and lack of sleep are closely connected to psychological well-being, which can also affect diet and appetite, as anyone who's ever gorged on cookies or potato chips when feeling anxious or sad can attest. Studies have demonstrated that some people eat more when affected by depression, anxiety, or other emotional disorders. In turn, overweight and obesity themselves can promote emotional disorders: If you repeatedly try to lose weight and fail, or if you succeed in losing weight only to gain it all back, the struggle can cause tremendous frustration over time, which can cause or worsen anxiety and depression. A cycle develops that leads to greater and greater obesity, associated with increasingly severe emotional difficulties.

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Do fat-adapted diets work?

But despite the hype, little evidence suggests that fat-adapted diets really improve athletic performance.

When the body doesn't have enough carbohydrates, it does increase its breakdown of fat, according to a 2015 study in the journal Metabolism Clinical and Experimental. In that study, ultra-endurance marathoners who were on an extremely low-carb diet could burn fat at twice the rate of those who were on a high-carb diet.

Still, low-carb, high-fat diets almost always lead to lower performance, according to more than a dozen studies conducted from 1960s to the 2000s. Because fat metabolism requires more chemical reactions in cells than metabolizing carbs does, it takes longer to produce the same amount of energy, meaning people who switch to burning fat can only exercise at a lower intensity compared to those who are burning carbs. [Infographic: What Is VO2 Max?]

In some of the most definitive work on this subject, Louise Burke, an exercise physiologist at the Australian Institute of Sport, and her colleagues conducted a study of low-carbohydrate and high-carbohydrate diets for elite race walkers. Her work has found that low-carb diets reduced performance.

And cycling between a low- and high-carb diet, as many mixed martial artists may do, probably doesn't help performance either, said Melinda Manore, a biologist and nutrition scientist at Oregon State University who studies how exercise affects nutritional needs.

That's because going on a low-carb diet changes how many enzymes the body makes to burn carbohydrates, and it can take several days to reverse this. On the day of a fight, for instance, people on a low-carb diet won't be able to utilize their glycogen stores as well to perform at high intensity, she said.

Fat-adapted diets may work OK for some ultramarathoners or extreme endurance athletes who need to work out at low intensity for long periods of time. However, studies also suggest that people on high-carb diets can get excellent results in similar endurance challenges, Jeukendrup said.

Beyond that, low-carb diets are often difficult to follow. Consuming no carbs means no fruits, veggies or whole grains, Manore said. One of the competitive race walkers in Burke's study took to eating sticks of butter, according to a recent interview.

"Most athletes hate it. They can't stay on it. They don't feel good," Manore said. "It's just not practical."

Editor's Note: This story was edited to update Asker Jeukendrup's affiliation. He is no longer with the Gatorade Sports Science Institute.