Many Americans exercise and go on diets to reduce their amount of body fat, yet over half of the adults in the United States are overweight…That’s 97 million people who have too much fat.
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. Other locations depend upon whether you are a man or woman:
An adult man tends to carry body fat in his chest, abdomen and buttocks.
An adult woman tends to carry fat in her breasts, hips, waist and buttocks.
The difference in fat location comes from the sex hormones estrogen and testosterone. Your body contains two types of fat tissue:
- White fat, which is important in energy metabolism, heat insulation and mechanical cushioning.
- Brown fat, which is found mostly in newborn babies, between the shoulders; important for thermogenesis (making heat).
Fat tissue is made up of fat cells. Fat cells 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.
- Brown fat cells are somewhat smaller, are loaded with mitochondria and are composed of several smaller fat droplets. The mitochondria are able to generate heat.
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 do not multiply after puberty. As your body stores more fat, the number of fat cells remains the same; each fat cell simply gets bigger.
When you eat food that contains fat, it goes through your stomach and intestines. In the intestines, the following happens:
- Large fat droplets get mixed with bile salts from your 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.
- 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.
- These parts get absorbed into the cells lining your intestine.
- 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.
- The chylomicrons are released into the lymphatic system — they do not go directly into your bloodstream because they are too big to pass through the wall of the capillary.
The lymphatic system eventually merges with the veins, at which point the chylomicrons pass into the bloodstream.
Chylomicrons do not last long in your 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. The activity of lipoprotein lipases depends upon the levels of insulin in your body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive.
When you eat a candy bar or a meal, the presence of glucose, amino acids or fatty acids n 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 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 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 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.
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 exercising your body must draw on its internal energy stores of complex carbohydrates, fats and proteins. 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 defence 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 your blood, and travel to your liver through the bloodstream. Once in your liver, the glycerol and fatty acids can be either further broken down or used to make glucose.
We see pure fats in three places at the grocery store:
In the vegetable oil aisle you see oils created from different seeds and nuts. There is corn oil, safflower oil, peanut oil, canola oil, and olive oil. All seeds and nuts contain some amount of oil, because oil is a very good way to store energy. By the way, the only difference between oil and fat is whether or not it is a solid at room temperature.
In the meat aisle, you can look at different cuts of meat and see them outlined by a layer of white, solid fat created by the animal to store energy.
In the dairy aisle you see butter and margarine, which are fats made from cream or vegetable oils, respectively.
The rest of the grocery store is of course, filled with fats and oils, although they are less obvious. Potato chips and French fries are cooked in oil, cookies and cakes contain fats and oils, and so on. This is how we eat the fat we need every day. And we do need fat to survive.
Most of what you hear about right now points to mono-unsaturated fats as the good fats. Olive oil and canola oil are both mono-unsaturated. Mono-unsaturated fats are thought to lower cholesterol.
The fats to steer clear of are the saturated fats. Saturated fats are bad because they clog your arteries. Partially hydrogenated vegetable oils (which are artificially saturated fats) are now considered totally evil, both because of the saturation and a side effect of hydrogenation called trans fatty acids.
There is a class of fatty acids called essential fatty acids that your body cannot manufacture. Because your body cannot manufacture these, they must come in from the food you eat.
Essential fatty acids fall into two groups: omega-3 and omega-6. All essential fatty acids are polyunsaturated. Omega-6 fatty acids are everywhere: corn oil, sunflower oil and soybean oil. Omega-3 fatty acids are harder to find. Things like flax seeds, pumpkin seeds and walnuts are high in omega-3 fatty acids, as are salmon, trout and tuna. The current thinking is that these two fats need to be balanced in the diet at a ratio like 1-to-1 or 2-to-1, rather than the normal 20-to-1 ratio seen in most Western diets. And the only way to do that is to supplement your diet with omega-3 vegetable oils or to start eating fish in a big way (meaning two or three times a week).
Limit your fat intake to between 25 and 30 percent of the total calories you consume. Do not try to cut fat intake altogether, because you do need the essential fatty acids. When consuming fat, try to focus on mono-unsaturated fats like olive oil and canola oil, or on essential fatty acids. When consuming essential fatty acids, try to balance your intake of omega-6 and omega-3 fatty acids. Do that by consuming tuna/salmon/trout or omega-3 oils like flax seed oil.
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, and the best way to maintain a healthy weight is; to eat a balanced diet, do not eat excessively and to exercise regularly.
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