IS THERE AN INDIVIDUAL SUSCEPTIBILITY TO BE OBESE?
Obesity is a complex disease in which external factors (diet and physical activity) and internal factors (genetics, sex and race) appear to interact. Similarly to the way in which a given life style that favours a positive energy balance would cause, in prone individuals, increased predisposition to develop obesity.
Genetic Susceptibility
Studies have been carried out in obese families, twins and adoptions with the aim of finding out the degree of heredity in the distribution of fat and obesity. A greater association has been observed between identical twins than between non-identical twins. Other studies of families have shown that genetic heredity would account for 30% of the obesity of the individual. In like manner, the degree of body fat of the adopted individual correlates up to 30% with that of the biological parents, but not so with his or her adoptive family. It thus appears that genetic heredity would also be responsible for abdominal fat up to 50-60%.
Even though not all the genes involved are known and it is not known how these act or interact for the development of obesity, there are different mechanisms whereby genetic susceptibility cold influence on the control of body weight: tendency to low basal metabolic rate, low level of fat utilisation by the body, poor appetite control, sensitivity to diminished insulin, predisposition to spontaneous physical activity, muscle composition, etc.
Non-Genetic Susceptibility
a) Sex: A female undergoes a series of physiological processes that contribute towards higher fat deposits and which occur mainly to maintain her reproductive capacity. At puberty, females show preference to consume carbohydrates whereas males prefer to consume proteins; late on in life, there is increased consumption of fats in both sexes, although it occurs earlier and more intensively in females.
b) Race: There are several ethnic groups that have special susceptibility to the development of obesity when exposed to an adequate setting. Among these groups, Pima Indians from Arizona and Australian aborigines, show a greater tendency when they leave their traditional life in favour of the diet and sedentary life styles of industrialised society. There are other factors that influence the development of obesity in minorities in developed countries (such as Afro-Americans and gypsies) where the higher obesity rates appear in poorer more depressed societal classes as fat-rich foods are less expensive.