It
is more reasonable to postulate that energy balance reflects the operation
of a physiologic regulatory, or homeostatic, mechanism." This homeostatic
set point is strongly influenced by genetics, as shown by studies of twins,
adoption studies, and metabolic studies.
Weigle suggests that body weight is set at the point of balance between
various feedback loops regulating adipose mass. The genetic influence could
be mediated by circulating factors or factors that regulate satiety. Individuals with a high set point express lower amounts of these factors and
thus have to gain relatively more adipose tissue before appetite and energy
expenditure balance. It is extraordinarily difficult to "cure" obesity by
dietary energy restriction. Indeed, the vast majority of patients who lose
weight through dieting regain that weight, indicating that the
weight-regulating system is very strong. "Only persons with incredibly
strong will power or the ability to tolerate physical discomfort are likely
to be successful in this attempt to defeat a homeostatic mechanism," says
Weigle.

Dieting is not only ineffectual, it carries risks. Severely
energy-restricted or unbalanced diets are linked to deficiency syndromes,
gallstones, arrhythmias, and sudden cardiac death. Even balanced diets lead
to chronic fatigue, impaired concentration, cold intolerance, mood changes,
and malaise as weight drops below the set point. Decreases in fat-free mass
are associated with loss of muscle strength and endurance. Calorie
restriction in children can restrict the growth of lean muscle mass, not a
good way to prevent obesity in adulthood. Cycles of dietary deprivation
followed by refeeding -- "yo-yo" dieting -- may contribute to hypertension,
congestive heart failure, and peripheral edema. And yo-yo dieting may
enhance metabolic efficiency, thus promoting weight gain. It may also lead
to low self-esteem as the dieter fails to either lose weight or maintain a
weight loss. Finally, health-care providers with unrealistic expectations
about weight loss may fail to treat true health hazards, such as
obesity-related diabetes, hypertension, and hyperlipidemia.

Weight reduction is usually recommended for patients whose weight is 20% or
more above desirable the weights listed in the Metropolitan Life Insurance
Company tables, although increased mortality is associated with weights more
than 40% above tabulated weights. Moreover, data used to formulate these
tables were taken from several studies, some with inadequate follow-up, and
some with inadequate control for confounding factors such as age, race,
smoking, body fat distribution, blood pressure, alcohol use, total and
HDL-cholesterol levels, gallbladder disease, blood glucose, and
triglycerides.