Dietary Fats: Types, Importance, and Addition to the Diet

I am writing this to address a new trend---eating too little fat. No doubt due to the low-fat fad of the 80's, many people today believe that losing fat can be as easy as cutting it out of the diet. It seems logical: eat less fat, have less fat. However, that's not the case. The fat you eat isn't just absorbed by the fat cells in your body, just eating less fat won't lead to fat loss, and just eating a lot of fat won't lead to fat gain. As many of you know or are discovering, the body is far more complicated than that. Fat is necessary for maintaining bodily functions, and by eating too little, you are actually endangering your health. So I'd like to explain the types of fat, why they're important, and how much you should shoot for eating. If you're interested, this information is coming from my NSCA exam book, Exercise Physiology book, and Biochemistry textbook.

TYPES OF FATS

Fats that are stored in the human body are called triglycerides. A triglyceride is made of three fatty acids attached to a glycerol molecule. You probably know that there are saturated, monounsaturated, polyunsaturated fats, and trans-fats. These names refer to the level of hydrogen saturation in the fatty acid group, or how many hydrogens are attached to the fatty acid molecule. These saturations cause a change in the shape of the triglyceride, which changes its behavior in the body.

Some Saturated Fats lower HDL (good cholesterol) and increase LDL (bad cholesterol).
Monounsaturated Fats generally do not affect plasma cholesterol levels (those found in the blood).
Some Polyunsaturated Fats lower both HDL and LDL cholesterol.

Sources of saturated fat include animal meat and tropical oils (like coconut).
Sources of monounsaturated fat include olive, peanut, and canola oil.
Sources of polyunsaturated fat include soy, corn, and sunflower oil.

Trans-fats are created by pumping hydrogen into an unsaturated fat in order to give in properties similar to a saturated fat, like being solid at room temperature. These lipids are not found in nature. It is so named for its molecular structure; instead of remaining in its natural cis position (bent) a double-bond change causes it to become straight. Trans-fats *increase* LDL levels and *decrease* LDL levels, so they are arguably the most unhealthy fat to eat. They are found in margarines and many processed snacks. Evidence of TFA's in food includes "hydrogenated oils" in the ingredients.

**A word on cholesterol: Although it doesn't contain fatty acids, it is considered a lipid. You can obtain cholesterol through your diet, and your body produces its own cholesterol. It is also necessary for life.**

(LDL and HDL cholesterol are also types of fats, but those aren't directly related to the importance of eating fats, and explaining that would take forever, so I'm not explaining that today.)

IMPORTANCE OF FATS

So what do fats do that's so important? A LOT.

Hormones: Cholesterol is used in the production of estrogen, androgen, and progesterone--the sex hormones. (It is also used in the production of bile salts, which digest fat, and Vit. D).

Nervous System: The essential fatty acids (Omega 3 and 6, or linolenic and linoleic) are used in the formation of cell membranes, as well as proper development and function in the brain.

Energy: Fat contains 9 calories per gram. At rest, fat provides 70-90% of the body's energy requirements. That means that 70-90% of your BMR needs are met with fat. So, if your BMR is 1200, that's 840-1080 calories (93-120g) coming from fat *every day*. During the first 90 minutes of exercise, about 37% of your caloric needs are met by fat. Into the third hour of exercise, that increases to 50-62% of your caloric needs.

Protection of Organs: Up to 4% of the body's fat acts as a shock insulator to your organs. Subcutaneous fat, found right under the skin, also offers insulation to regulate body temperature in the cold.

Vitamin Absorption: Dietary fats serve as carriers for the fat-soluble vitamins A, D, E and K; in order to absorb the RDA of these vitamins, about 20g of fat per day is necessary (JUST for this function).

Hunger/Blood Sugar Control: Gastric emptying time, or time required for food to leave the stomach, is about 3.5 hours for lipids. This promotes feelings of satiety. Also, lipids help slow the release of sugar into the blood stream, preventing spikes in blood sugar that lead to overcompensation of insulin and then low blood sugar. This is a great defense against insulin-resistance as well as hunger.

ADDITION TO THE DIET

It is recommended that fat constitute 20-30% of your daily calories. Two-thirds of that should come from unsaturated sources, and one third should come from saturated sources. However, during endurance exercise, eating up to 50% of daily calories from fat has not been shown to negatively affect blood lipid levels (like cholesterol and triglycerides in the blood).

Diets containing 10% of calories from fat have been shown to worsen lipid profiles, and may also decrease testosterone production, which leads to muscle loss and a decreased metabolism (this applies to women too--we produce testosterone).

EATING TOO LITTLE FAT IS DANGEROUS AND UNHEALTHY.
Fat loss comes from a CALORIC DEFICIT, not from just cutting fat to unhealthy levels. If you are in a caloric deficit, eating a high percentage of your calories from fats will not cause fat gain. Some diets, like the Ketogenic diet used to treat epilepsy in children, rely almost entirely on fat for energy, and do not result in fat gain. Fats aren't dangerous or unhealthy (with the possible exception of trans-fats). Don't avoid them. Use them to your advantage.