Fatty foods that have more energy-producing power, weight for weight, than other types of food. Animal fat is a mixture in varying proportions of stearic, palmitic, and oleic acids combined with glycerine. Butter contains about 80 per cent of fat; ordinary cream, 20 per cent; and rich cream 40 per cent – whilst olive oil is practically a pure form of fat. When taken to a large extent in the diet, fat requires to be combined with a certain proportion of either CARBOHYDRATE or PROTEIN in order that it may be completely consumed, otherwise harmful products, known as KETONES, may form in the blood. Each gram of fat has an energy-producing equivalent of 9.3 Calories (see CALORIE).
Fats are divided into saturated fats – that is, animal fats and dairy produce – and unsaturated fats, which include vegetable oils from soya bean, maize and sunflower, and marine oils from fish (e.g. cod-liver oil). (See also ADIPOSE TISSUE; LIPID; OBESITY.)
Most of the body's fat is stored in ADIPOSE TISSUE beneath the skin and around various internal organs. Additionally some is stored in liver, muscle and other cellular structures such as bone marrow (see BONE). Various methods can be used to estimate the body's fat content but all are indirect and not very accurate, depending as they do on hard-to-measure differences in composition between fat and lean tissues. The average body fat of healthy young men and women is below 20 per cent and 25 per cent respectively of their body weight. In economically developed countries, middle-aged men and women usually undergo a steady increase in body fat. This is probably not a feature of ageing, however, since in developing nations, which have different diets and greater levels of physical activity, increased age does not bring with it an increase in body fat. One widely used means to estimate whether a person has excess fat is to measure his or her skinfold thickness on the arms and torso. The distribution of fat can be a pointer to certain disorders: for example, those adults in whom fat is deposited around the waist rather than the hips — are particularly susceptible to disease of the CARDIOVASCULAR SYSTEM and to DIABETES MELLITUS.
Adipose tissue is deposited when a person eats more food than they use up by exercise and the normal activity of body functioning (metabolism). Excessive quantities of adipose tissue result in OBESITY, an increasingly serious problem among all age groups, including children.