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Fats

Fats

Introduction

With an energy content of 9 kcal/g fat, fat is a much denser source of energy than carbohydrate and protein. Fats perform several important functions in the body such as: being an essential component of cell membranes, walls and nerve fibers, supporting and cushioning vital organs, providing 70% of energy for the body in the resting state, assisting the absorption and transport of fat-soluble vitamins, and providing an insulating layer in the body to preserve body heat.

Fats are structures composed primarily of carbons and hydrogens with little oxygen, therefore they take longer to oxidize for energy. An important fuel energy during exercise are the free fatty acids (FFA) which are obtained from muscular, plasma, and adipose tissue fat sources.

FFA are long chains of carbon and hydrogen ending with a carboxyl group. Exercise increases lipid utilization of athletes. Extensive physical conditioning and endurance training have enhanced the capacity of skeletal muscles to oxidize FFA from adipose tissue, intramuscular fluid and plasma and thereby saving glycogen sources. For low intensity exercises such as baseball or golf, FFA oxidation is the primary source of fuel for energy.

There are three primary forms of fat:

glycerides
phospholipids
sterols

Glycerides

The most abundant form of fat found in foods and in animal tissue are the triglycerides, where 95-98% of all fats consumed are in this form. Fat is stored in the body for fuel as triglycerides, the structure of which consists of three molecules of fatty acids and a glycerol molecule (CH2OH-CHOH-CH2OH). Most of the triglycerides are stored in adipose tissue (99%), and in small amounts in liver and muscle.

The fatty acids can either be of two types: saturated and unsaturated. Saturated fats have all their carbons bound to two hydrogen atoms, and these are primarily found from animal sources (meats and dairy products) and in some tropical oils (e.g. palm and coconut) and are solid. Unsaturated fats have one (monounsaturated) or more (polyunsaturated) double bonds between carbons. Unsaturated fats are liquid and are derived from fish and vegetable oil.

There are two forms of fatty acids that cannot be synthesized by the body and thus must be obtained in the diet: linoleic and linoleic acid. These essential fatty acids (EFA) are found mostly in vegetable oils, leafy vegetables, and in fish and seafoods. The EFA have a common structural feature: they contain a di-vinyl-methylene interrupted fragment. This structure makes EFA's essential to all animals.

Phospholipids & Sterols

Phospholipids and sterols are not as abundantly found in the diet, only about 5% of fats consumed are of these two types. Phospholipids are similar to triglycerides, except they have one fatty acid replaced with a phosphate molecule and a nitrogenous component (e.g. choline).

Cholesterol is the most commonly known sterol, which are ring structures containing carbon, hydrogen and oxygen. Phospholipids are found in the same sources as the triglycerides and cholesterol are found naturally in animal products such as red meat, whole milk and egg yolks.

Fat Intake Concern

High intake of saturated fats and cholesterol have been associated with high blood pressure, coronary heart disease, obesity and possible cancer. Athletes should be aware no more than 30% of their caloric intake should be from fat when trying to obtain sufficient calories for physical activity. High-energy requiring sports (e.g. marathon running and cycling) often need increases of fat content in their diets. There are supplements containing high-fat ("weight-gainers").

References

Diet and Health: Implications for Reducing Chronic Disease Risk. Committee on Diet and Health Food and Nutrition Board and Commission on Life Sciences and National Research Council. National Academic Press, Washington D.C. 1989. pp. 139-142; 159;259; 273-276; 291-2.

Buskirk, E. Some Nutritional Considerations in the Conditioning of Athletes. Ann. Rev. Nutr. Darby, Broquist and Olson, Eds. 1981. 1:319-50.

Buskirk, E.R. Diet and Athletic Performance. Postgrad. Med. 1977. 61:229-36.

Costill, D. Nutrition and Dietetics. The Olympic Book of Sports Medicine. Vol.1. Dirix, Knuttgen, & Tittel. Eds. Blackwell Scientific Publications, London. 1988. 603-635.

Costill, D.L. and J.M. Miller. Nutrition for endurance sport: carbohydrate and fluid balance. 1980. Int. J. Sports Med. 1: 2-14.

Levy, R.I. et al. Nutrition, lipids and coronary heart disease: a global view. 1979. Raven. New York. 1-566.

Linder, Maria. Nutrtional Biochemistry and Metabolism with Clinical Applications. 1985. Elsevier, New York. pp.15-31; 33-39; 51-56; 69-73.

 


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