Obesity

Obesity

Obesity is the most common and most expensive nutritional

problem in the United States. A convenient and reliable indicator

of body fat is the

body weight (in kilograms) divided by the square of height (in

meters). Values above 25 are abnormal. Individuals with values

of 25–30 are overweight, and those with values > 30 are

obese. In the United States, 55% of the population are overweight

and 22% are obese. The incidence of obesity is also increasing

in other countries. Indeed, the Worldwatch Institute

has estimated that although starvation continues to be a

problem in many parts of the world, the number of overweight

people in the world is now as great as the number of

underfed. Obesity is a problem because of its complications.

It is associated with accelerated atherosclerosis and an increased

incidence of gallbladder and other diseases. Its association

with type 2 diabetes is especially striking. As weight

increases, insulin resistance increases and frank diabetes appears.

At least in some cases, glucose tolerance is restored

when weight is lost. In addition, the mortality rates from

many kinds of cancer are increased in obese individuals. The

causes of the high incidence of obesity in the general population

are probably multiple. Studies of twins raised apart show

a definite genetic component. It has been pointed out that

through much of human evolution, famines were common,

and mechanisms that permitted increased energy storage as

fat had survival value. Now, however, food is plentiful in many

countries, and the ability to gain and retain fat has become a

liability. As noted above, the fundamental cause of obesity is

still an excess of energy intake in food over energy expenditure.

If human volunteers are fed a fixed high-calorie diet,

some gain weight more rapidly than others, but the slower

weight gain is due to increased energy expenditure in the

form of small, fidgety movements

thermogenesis; NEAT).

slow but steady rate throughout adult life. Decreased physical

activity is undoubtedly a factor in this increase, but decreased

sensitivity to leptin may also play a role.

body mass index (BMI), which is(nonexercise activityBody weight generally increases at a