How Fat Cells Work

A little more than half of the adults in the United States are overweight. Statistics show that an incredible 65.2 percent of the U.S. population is considered to be "overweight" or "obese." According to the Centers for Disease Control and Prevention (CDC), obesity and overweight status is determined in adults by finding a person's "Body Mass Index" or BMI.

BMI is a calculation that takes into consideration both a person's body weight and height to determine whether they are underweight, overweight or at a healthy weight. An adult who is considered "overweight" has a BMI somewhere between 25 and 29.9. An adult with a BMI of at least 30 is considered "obese." This measurement is used because it's typically a good indicator of body fat.

Whether due to concern for related health risks (high blood pressure, heart disease, diabetes, sleep apnea, respiratory problems, etc.), or just for sheer aesthetics, many Americans worry about fat. In fact, at this very moment, thousands of Americans are exercising or dieting to reduce their amount of body fat. But have you ever wondered what fat is? When a person "gets fat" -- gains weight -- what is actually happening inside the person's body? What are "fat cells" and how do they work?

Fat, or adipose tissue, is found in several places in your body. Generally, fat is found underneath your skin (subcutaneous fat). There's also some on top of each of your kidneys. In addition to fat tissue, some fat is stored in the liver, and an even smaller amount in muscle.

Where fat is concentrated in your body depends upon whet her you are a man or woman:

An adult man tends to carry body fat in his chest, abdomen and buttocks, producing an "apple" shape.

An adult woman tends to carry fat in her breasts, hips, waist and buttocks, creating a "pear" shape.

The difference in fat location comes from the sex hormones estrogen and testosterone. Fat cells are formed in the developing fetus during the third trimester of pregnancy, and later at the onset of puberty, when the sex hormones "kick in." It is during puberty that the differences in fat distribution between men and women begin to take form. One amazing fact is that fat cells generally do not generate after puberty -- as your body stores more fat, the number of fat cells remains the same. Each fat cell simply gets bigger! (There are two exceptions: the body might produce more fat cells if an adult gains a significant amount of weight or has liposuction performed.)

In this article, we will look at how fat cells store fat and how they get rid of it. See the next page to learn more.

Body Fat Basics

The human body contains two types of fat tissue:

White fat is important in energy metabolism, heat insulation and mechanical cushioning.

Brown fat is found mostly in newborn babies, between the shoulders, and is important for thermogenesis (making heat). Since adult humans have little to no brown fat, we'll concentrate on white fat in this article. See the bottom of this page for more on brown fat.

Fat tissue is made up of fat cells, which are a unique type of cell. You can think of a fat cell as a tiny plastic bag that holds a drop of fat. White fat cells are large cells that have very little cytoplasm, only 15 percent cell volume, a small nucleus and one large fat droplet that makes up 85 percent of cell volume.

How Fat Enters Your Body

When you eat food that contains fat, mostly triglycerides, it goes through your stomach and intestines. In the intestines, the following happens:

1.Large fat droplets get mixed with bile salts from the gall bladder in a process called emulsification. The mixture breaks up the large droplets into several smaller droplets called micelles, increasing the fat's surface area.

2.The pancreas secretes enzymes called lipases that attack the surface of each micelle and break the fats down into their parts, glycerol and fatty acids.

3.These parts get absorbed into the cells lining the intestine.

4.In the intestinal cell, the parts are reassembled into packages of fat molecules (triglycerides) with a protein coating called chylomicrons. The protein coating makes the fat dissolve more easily in water.

5.The chylomicrons are released into the lymphatic system -- they do not go directly into the bloodstream because they are too big to pass through the wall of the capillary.

6.The lymphatic system eventually merges with the veins, at which point the chylomicrons pass into the bloodstream.

You might be wondering why fat molecules get broken down into glycerol and fatty acids if they're just going to be rebuilt. This is because fat molecules are too big to easily cross cell membranes. So when passing from the intestine through the intestinal cells into the lymph, or when crossing any cell barrier, the fats must be broken down. But, when fats are being transported in the lymph or blood, it is better to have a few, large fat molecules than many smaller fatty acids, because the larger fats do not "attract" as many excess water molecules by osmosis as many smaller molecules would.

In the next section, we'll look at how fat is stored in your body.

Fat Storage

In the last section, we learned how fat in the body is broken down and rebuilt into chylomicrons, which enter the bloodstream by way of the lymphatic system.

Chylomicrons do not last long in the bloodstream -- only about eight minutes -- because enzymes called lipoprotein lipases break the fats into fatty acids. Lipoprotein lipases are found in the walls of blood vessels in fat tissue, muscle tissue and heart muscle.

Insulin

When you eat a candy bar or a meal, the presence of glucose, amino acids or fatty acids in the intestine stimulates the pancreas to secrete a hormone called insulin. Insulin acts on many cells in your body, especially those in the liver, muscle and fat tissue. Insulin tells the cells to do the following:

Absorb glucose, fatty acids and amino acids

Stop breaking down:

glucose, fatty acids and amino acids

glycogen into glucose

fats into fatty acids and glycerol

proteins into amino acids

Start building:

glycogen from glucose

fats (triglycerides) from glycerol and fatty acids

proteins from amino acids

The activity of lipoprotein lipases depends upon the levels of insulin in the body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive.

The fatty acids are then absorbed from the blood into fat cells, muscle cells and liver cells. In these cells, under stimulation by insulin, fatty acids are made into fat molecules and stored as fat droplets.

It is also possible for fat cells to take up glucose and amino acids, which have been absorbed into the bloodstream after a meal, and convert those into fat molecules. The conversion of carbohydrates or protein into fat is 10 times less efficient than simply storing fat in a fat cell, but the body can do it. If you have 100 extra calories in fat (about 11 grams) floating in your bloodstream, fat cells can store it using only 2.5 calories of energy. On the other hand, if you have 100 extra calories in glucose (about 25 grams) floating in your bloodstream, it takes 23 calories of energy to convert the glucose into fat and then store it. Given a choice, a fat cell will grab the fat and store it rather than the carbohydrates because fat is so much easier to store.

Next, we'll look at how your body breaks down fat.

Breaking Down Fat

When you are not eating, your body is not absorbing food. If your body is not absorbing food, there is little insulin in the blood. However, your body is always using energy; and if you're not absorbing food, this energy must come from internal stores of complex carbohydrates, fats and proteins. Under these conditions, various organs in your body secrete hormones:

pancreas - glucagon

pituitary gland - growth hormone

pituitary gland - ACTH (adrenocorticotropic hormone)

adrenal gland - epinephrine (adrenaline)

thyroid gland - thyroid hormone

These hormones act on cells of the liver, muscle and fat tissue, and have the opposite effects of insulin.

When you are not eating, or you are exercising, your body must draw on its internal energy stores. Your body's prime source of energy is glucose. In fact, some cells in your body, such as brain cells, can get energy only from glucose.

The first line of defense in maintaining energy is to break down carbohydrates, or glycogen, into simple glucose molecules -- this process is called glycogenolysis. Next, your body breaks down fats into glycerol and fatty acids in the process of lipolysis. The fatty acids can then be broken down directly to get energy, or can be used to make glucose through a multi-step process called gluconeogenesis. In gluconeogenesis, amino acids can also be used to make glucose.

In the fat cell, other types of lipases work to break down fats into fatty acids and glycerol. These lipases are activated by various hormones, such as glucagon, epinephrine and growth hormone. The resulting glycerol and fatty acids are released into the blood, and travel to the liver through the bloodstream. Once in the liver, the glycerol and fatty acids can be either further broken down or used to make glucose.

Losing Weight and Losing Fat

Your weight is determined by the rate at which you store energy from the food that you eat, and the rate at which you use that energy. Remember that as your body breaks down fat, the number of fat cells remains the same; each fat cell simply gets smaller.

Most experts agree that the way to maintain a healthy weight is:

Eat a balanced diet - appropriate amounts of carbohydrates, fat and protein

Do not eat excessively - for most people, a diet of 1,500 to 2,000 calories a day is sufficient to maintain a healthy weight

Exercise regularly

For more information on fat and your health, check out the links on the following page.

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How Cholesterol Works

What is Cholesterol?

Cholesterol is a waxy, fat-like compound that belongs to a class of molecules called steroids. It's found in many foods, in your bloodstream and in all your body's cells. If you had a handful of cholesterol, it might feel like a soft, melted candle. Cholesterol is essential for:

1.Formation and maintenance of cell membranes (helps the cell to resist changes in temperature and protects and insulates nerve fibers)
2.Formation of sex hormones (progesterone, testosterone, estradiol, cortisol)
3.Production of bile salts, which help to digest food
4.Conversion into vitamin D in the skin when exposed to sunlight.

The formation of cholesterol involves a series of complicated biochemical reactions that begin with the widespread 2-carbon molecule Acetyl CoA: Acetyl CoA (C2) --> mevalonate (C6) --> isopentenyl pyrophosphate (C5) --> squalene (C30) --> cholesterol (C27).

Cholesterol is made primarily in your liver (about 1,000 milligrams a day), but it is also created by cells lining the small intestine and by individual cells in the body.

Blood Cholesterol vs. Dietary Cholesterol

It may surprise you to know that our bodies make all the cholesterol we need. When your doctor takes a blood test to measure your cholesterol level, the doctor is actually measuring the amount of circulating cholesterol in your blood, or your blood cholesterol level. About 85 percent of your blood cholesterol level is endogenous, which means it is produced by your body. The other 15 percent or so comes from an external source -- your diet. Your dietary cholesterol originates from meat, poultry, fish, seafood and dairy products. It's possible for some people to eat foods high in cholesterol and still have low blood cholesterol levels. Likewise, it's possible to eat foods low in cholesterol and have a high blood cholesterol level.

So, why is there so much talk about cholesterol in our diet? It's because the level of cholesterol already present in your blood can be increased by high consumption of cholesterol and saturated fat in your diet. This increase in dietary cholesterol has been associated with atherosclerosis, the build-up of plaques that can narrow or block blood vessels. (Think about what happens to your kitchen drain pipes when you pour chicken fat down the sink.) If the coronary arteries of the heart become blocked, a heart attack can occur. The blocked artery can also develop rough edges. This can cause plaques to break off and travel, obstructing blood vessels elsewhere in the body. A blocked blood vessel in the brain can trigger a stroke.

The average American man eats about 360 milligrams of cholesterol a day; the average woman eats between 220 and 260 milligrams daily. So how are we doing? The American Heart Association recommends that we limit our average daily cholesterol intake to less than 300 milligrams. Obviously, people with high levels of cholesterol in the blood should take in even less.

Good and Bad Cholesterol

Comments about "good" and "bad" cholesterol refer to the type of carrier molecule that transports the cholesterol. These carrier molecules are made of protein and are called apoproteins載脂蛋白. They are necessary because cholesterol and other fats (lipids) can't dissolve in water, which also means they can't dissolve in blood. When these apoproteins are joined with cholesterol, they form a compound called lipoproteins. The density of these lipoproteins is determined by the amount of protein in the molecule. "Bad" cholesterol is the low-density lipoprotein (LDL), the major cholesterol carrier in the blood. High levels of these LDLs are associated with atherosclerosis. "Good" cholesterol is the high-density lipoprotein (HDL); a greater level of HDL--think of this as drain cleaner you pour in the sink--is thought to provide some protection against artery blockage.

A high level of LDL in the blood may mean that cell membranes in the liver have reduced the number of LDL receptors due to increased amounts of cholesterol inside the cell. After a cell has used the cholesterol for its chemical needs and doesn't need any more, it reduces its number of LDL receptors. This enables LDL levels to accumulate in the blood. When this happens, the LDLs begin to deposit cholesterol on artery walls, forming thick plaques. In contrast, the HDLs--the "good" guys--act to remove this excess cholesterol and transport it to the liver for disposal.

A third group of carrier molecules, the very low-density lipoproteins (VLDL) are converted to LDL after delivering triglycerides to the muscles and adipose (fat) tissue.

The levels of HDL, LDL and total cholesterol are all indicators for atherosclerosis and heart attack risk. People who have a cholesterol level of 275 or greater (200 or less is desirable) are at significant risk for a heart attack, despite a favorable HDL level. In addition, people who have normal cholesterol levels but low HDL levels are also at increased risk for a heart attack.

Cholesterol Risk Factors

There are a number of factors that influence a person's cholesterol levels. They include diet, age, weight, gender, genetics, diseases and lifestyle.

Diet

There are two dietary factors associated with increases in blood cholesterol levels:

Eating foods that are high in saturated fats, even if the fats themselves do not contain cholesterol. (These include foods containing high levels of hydrogenated vegetable oils, especially palm and coconut oils, avocados and other high-fat foods of vegetable origin.)

Eating foods containing high levels of cholesterol. (This group includes eggs and red meat--the most maligned of the cholesterol culprits--as well as lard and shrimp. These foods can significantly raise blood cholesterol levels, especially when combined with foods that are high in saturated fat.)

It's important to note that only foods of animal origin contain cholesterol. Lack of awareness of this fact has led to some confusing labels at the grocery store. For example, some items that are high in saturated fats from plant sources bear labels claiming that they are 100 percent cholesterol free. The statement may be true, but it's generally misleading because it implies that the product is definitely beneficial to your health.

Age

The blood levels of cholesterol tend to increase as we age--a factor doctors consider when deciding treatment options for patients with certain cholesterol levels.

Weight

People who are overweight are more likely to have high blood cholesterol levels. They also tend to have lower HDL levels. The location of the excess weight also seems to play a role in cholesterol levels. A greater risk of increased cholesterol levels occurs when that extra weight is centered in the abdominal region, as opposed to the legs or buttocks.

Gender

Men tend to have higher LDL levels and lower HDL levels than do women, especially before age 50. After age 50, when women are in their post-menopausal years, decreasing amounts of estrogen are thought to cause the LDL level to rise.

Genetics

Some people are genetically predisposed to having high levels of cholesterol. A variety of minor genetic defects can lead to excessive production of LDLs or a decreased capacity for their removal. This tendency towards high cholesterol levels is often passed on from parents to their children. If your parents have high cholesterol, you need to be tested to see if your cholesterol levels are also elevated.

Diseases

Diseases such as diabetes can lower HDL levels, increase triglycerides and accelerate the development of atherosclerosis. High blood pressure, or hypertension, can also hasten the development of atherosclerosis, and some medications used to treat it can increase LDL and triglycerides and decrease HDL levels.

Lifestyle

Factors that negatively affect cholesterol levels also include high levels of stress, which can raise total cholesterol levels, and cigarette smoking, which can lower a person's HDL level as much as 15 percent. On the other hand, strenuous exercise can increase HDL levels and decrease LDL levels. Exercise also can help reduce body weight, which, in turn, can help reduce cholesterol. Recent research has shown that moderate alcohol use (one drink per day for women, two drinks a day for men) can raise HDL cholesterol and therefore reduce the risk of heart attack. Despite such research, it is difficult to recommend the habitual use of alcohol, because there are also negative health consequences associated with alcohol use and a high potential for abuse.

Always remember that risk factors for high cholesterol and cardiovascular disease don't exist in a vacuum--they tend to amplify each other. Reducing the risk of a cardiovascular disease involves eliminating all of the risk factors that we can control and seeking medical advise for those we can't.

Cholesterol Testing and Prevention

How often should I have my cholesterol levels tested?

You should get your cholesterol tested every three to five years, more often if you have high cholesterol levels. Please refer to the table below for guidelines for total cholesterol, LDL and HDL levels.

What can I do to reduce my cholesterol?

There are several steps you can take to reduce your cholesterol levels. The first is to eat a low-fat, low-cholesterol diet. That means keeping your total fat consumption--saturated, polyunsaturated and monounsaturated--to fewer than 30 percent of your daily intake of calories. (See How Fat Works for details.) Remember to keep your cholesterol intake to fewer than 300 milligrams per day. Saturated fats contained in butter, whole milk, hydrogenated oils, chocolate shortening, etc. should comprise no more than one third of your total fat consumption. To reduce your total fat and cholesterol intake, limit your consumption of meats such as beef, pork, liver and tongue (always trim away excess fat). In addition, avoid cheese, fried foods, nuts and cream, and try to curb your intake of eggs to no more than four per week. Try to eat meatless meals several times a week, use skim milk and include fish in your diet. Eat a wide variety of vegetables, pasta, grains and fruit. Another good tip is to look at the package label of the foods you buy, and restrict your choices to foods containing 3 grams of fat or less per serving.

There is evidence that water-soluble fibers can aid in lowering cholesterol; these foods include the fiber in oat or corn bran, beans and legumes, pectin found in apples and other fruits, and guar that is used as a thickener. Although highly touted by the media and health food stores, the phospholipid Lecithin has not been confirmed as a reducer of blood cholesterol levels.

If you are overweight, trying to lose weight and including aerobic exercise in your routine can help raise those desirable HDL levels. Diet and exercise alone can decrease cholesterol levels by up to 15 percent.

It probably comes as no surprise to you that, if you smoke, you should quit to avoid a wide range of health problems, including lower HDL levels and increased risk of heart attack.

Medicating High Cholesterol

Sometimes positive changes in diet, lifestyle and exercise are not enough. In these cases, doctors may consider the use of medication that lowers cholesterol. The decision to have a patient begin medication is often based on high levels of LDL cholesterol and other risk factors for cardiovascular disease. For example, medication may be indicated if your LDL level is over 190 or is over 160 and you have several other risk factors for cardiovascular disease.

Drugs that reduce LDL blood levels can prevent or reduce the build-up of artery-blocking plaques and can limit the possibility of the release of those plaques as dangerous blood clots. There are several types of drugs that can help reduce blood cholesterol levels. The most commonly prescribed are the statins, HMG-CoA reductase inhibitors, including:

Lovastatin (Mevacor)

Simvastatin (Zocor)

Atorvastatin (Lipitor), a new, highly potent drug

These drugs work within the liver to directly prevent the formation of cholesterol and can lower LDL cholesterol by as much as 40 percent. Research also shows that these drugs can reduce the risk of death from cardiovascular disease. Another major drug category is the resins, which bind bile acids, causing the liver to produce more of them and using up cholesterol in the process. By "tying" it up, these drugs make cholesterol less available in the blood. They include:

Cholestyramine (Questran)

Colestipol (Colestid)

The B vitamin Niacin, in high doses, can lower triglycerides and LDL levels and increase HDL levels. Niacin has been proven to reduce a person's risk of having a second heart attack. Last are the drugs in the fibrates category, which lower triglycerides and can increase HDL levels. These include:

Gemfibrozil (Lopid)

Fenofibrate (Tricor)

The decision to take cholesterol- or lipid-lowering drugs is not taken lightly by your doctor. These drugs can be fairly expensive and are often required for many years or even the rest of your life. It is also important to note that some of these drugs can have dangerous side effects, such as damage to the liver.

Adopting a healthy lifestyle and visiting your doctor regularly can help curb your risks of problem cholesterol. Have your cholesterol levels checked by a physician, rather than risk incorrectly interpreting numbers in self test kits currently on the market. Remember, cholesterol is necessary for life but it can also be very harmful and requires monitoring. So, watch your cholesterol and keep in mind that, for every 1 percent drop in your cholesterol level, your risk of heart attack is lowered by 2 percent.

For more information on cholesterol and related topics, check out the links on the next page.

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How Calories Work

Inside this Article
1. Introduction to How Calories Work
2. What is a Calorie?
3. What Calories Do
4. BMR
5. Your Caloric Needs
6. Calories, Fat and Exercise
7. Lots More Information
8. See all Weight Loss articles

For years now, calories have been all the rage -- people are counting them and cutti­ng them, and you'd be hard-pressed to find something at the supermarket that does not list its calories per serving somewhere on the package. But have you ever wondered what exactly a calorie is?
In this article, we'll find out what calories are and why we need them, and examine the relationship between calories and weight.

What is a Calorie?
A calorie is a unit of energy. We tend to associate calories with food, but they apply to anything containing energy. For example, a gallon (about 4 liters) of gasoline contains about 31,000,000 calories.
Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water 1 degree Celsius (1.8 degrees Fahrenheit). One calorie is equal to 4.184 joules, a common unit of energy used in the physical sciences.
Most of us think of calories in relation to food, as in "This can of soda has 200 calories." It turns out that the calories on a food package are actually kilocalories (1,000 calories = 1 kilocalorie). The word is sometimes capitalized to show the difference, but usually not. A food calorie contains 4,184 joules. A can of soda containing 200 food calories contains 200,000 regular calories, or 200 kilocalories. A gallon of gasoline contains 31,000 kilocalories.
The same applies to exercise -- when a fitness chart says you burn about 100 calories for every mile you jog, it means 100 kilocalories. For the duration of this article, when we say "calorie," we mean "kilocalorie."

Caloric Breakdown
· 1 g Carbohydrates: 4 calories
· 1 g Protein: 4 calories
· 1 g Fat: 9 calories

What Calories Do
Human beings need energy to survive -- to breathe, move, pump blood -- and they acquire this energy from food.
The number of calories in a food is a measure of how much potential energy that food possesses. A gram of carbohydrates has 4 calories, a gram of protein has 4 calories, and a gram of fat has 9 calories. Foods are a compilation of these three building blocks. So if you know how many carbohydrates, fats and proteins are in any given food, you know how many calories, or how much energy, that food contains.
If we look at the nutritional label on the back of a packet of maple-and-brown-sugar oatmeal, we find that it has 160 calories. This means that if we were to pour this oatmeal into a dish, set the oatmeal on fire and get it to burn completely (which is actually pretty tricky), the reaction would produce 160 kilocalories (remember: food calories are kilocalories) -- enough energy to raise the temperature of 160 kilograms of water 1 degree Celsius. If we look closer at the nutritional label, we see that our oatmeal has 2 grams of fat, 4 grams of protein and 32 grams of carbohydrates, producing a total of 162 calories (apparently, food manufacturers like to round down). Of these 162 calories, 18 come from fat (9 cal x 2 g), 16 come from protein (4 cal x 4 g) and 128 come from carbohydrates (4 cal x 32 g).
Our bodies "burn" the calories in the oatmeal through metabolic processes, by which enzymes break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids and the proteins into amino acids (see How Food Works for details). These molecules are then transported through the bloodstream to the cells, where they are either absorbed for immediate use or sent on to the final stage of metabolism in which they are reacted with oxygen to release their stored energy.
Click here for a simplified diagram of these metabolic processes.

BMR
Just how many calories do our cells need to function well? The number is different for every person. You may notice on the nutritional labels of the foods you buy that the "percent daily values" are based on a 2,000 calorie diet -- 2,000 calories is a rough average of what a person needs to eat in a day, but your body might need more or less than 2,000 calories. Height, weight, gender, age and activity level all affect your caloric needs. There are three main factors involved in calculating how many calories your body needs per day:
· Basal metabolic rate
· Physical activity
· Thermic effect of food
Your basal metabolic rate (BMR) is the amount of energy your body needs to function at rest. This accounts for about 60 to 70 percent of calories burned in a day and includes the energy required to keep the heart beating, the lungs breathing, the kidneys functioning and the body temperature stabilized. In general, men have a higher BMR than women. One of the most accurate methods of estimating your basal metabolic rate is the Harris-Benedict formula:
· Adult male: 66 + (6.3 x body weight in lbs.) + (12.9 x height in inches) - (6.8 x age in years)
· Adult female: 655 + (4.3 x weight in lbs.) + (4.7 x height in inches) - (4.7 x age in years)
(Note: The first number in the equation for females is, in fact, 655. Strange but true.)

Your Caloric Needs
As you now know, there are three main factors involved in calculating how many calories your body needs per day: your BMR, physical activity and the thermic effect of food.
The second factor in the equation, physical activity, consumes the next highest number of calories. Physical activity includes everything from making your bed to jogging. Walking, lifting, bending, and just generally moving around burns calories, but the number of calories you burn in any given activity depends on your body weight. Click here for a great table listing the calories expended in various physical activities and for various weights.
The thermic effect of food is the final addition to the number of calories your body burns. This is the amount of energy your body uses to digest the food you eat -- it takes energy to break food down to its basic elements in order to be used by the body. To calculate the number of calories you expend in this process, multiply the total number of calories you eat in a day by 0.10, or 10 percent. If you need some help determining how many calories you eat in a day, check out these sites:
· USDA National Nutrient Database
· Food Data
· Mike's Calorie And Fat Gram Chart
The total number of calories a body needs in a day is the sum of these three calculations. If you only want a rough estimate of your daily caloric needs, you can skip the calculations and click here.

Calories, Fat and Exercise
So what happens if you take in more or fewer calories than your body burns? You either gain or lose fat, respectively. An accumulation of 3,500 extra calories is stored by your body as 1 pound of fat -- fat is the body's way of saving energy for a rainy day. If, on the other hand, you burn 3,500 more calories than you eat, whether by exercising more or eating less, your body converts 1 pound of its stored fat into energy to make up for the deficit.
One thing about exercise is that it raises your metabolic rate not only while you're huffing and puffing on the treadmill. Your metabolism takes a while to return to its normal pace. It continues to function at a higher level; your body burns an increased number of calories for about two hours after you've stopped exercising.
Lots of people wonder if it matters where their calories come from. At its most basic, if we eat exactly the number of calories that we burn and if we're only talking about weight, the answer is no -- a calorie is a calorie. A protein calorie is no different from a fat calorie -- they are simply units of energy. As long as you burn what you eat, you will maintain your weight; and as long as you burn more than you eat, you'll lose weight.
But if we're talking nutrition, it definitely matters where those calories originate. Carbohydrates and proteins are healthier sources of calories than fats. Although our bodies do need a certain amount of fat to function properly -- an adequate supply of fat allows your body to absorb the vitamins you ingest -- an excess of fat can have serious health consequences. The U.S. Food and Drug Administration recommends that a maximum of 30 percent of our daily calories come from fat. So, if you eat 2,000 calories a day, that's a maximum of 600 calories from fat, or 67 grams of fat, per day. However, many doctors and nutritionists now set the maximum number of fat calories at 25 percent of our daily caloric intake. That's 56 grams of fat per day for a 2,000 calorie diet.
Here are some calorie and fat contents that may surprise you:
For more information on calories, dieting, nutrition and related topics, check out the links on the next page!

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