Although the involvement of genes in weight and body shape is obvious, they cannot explain the recent increase in obesity rates.

In the last few decades, genes have not changed but the environment surely has. There are five leading environmental culprit causing the worldwide weight-gain epidemic.

  1. the increased abundance of inexpensive, diverse, high-fat foods
  2. the tendency to eat high-calorie food on the go rather than unhurried meals
  3. the increase in energy-saving technology, such as remote controls
  4. the speed and convenience of driving rather than walking or biking
  5. the preference for watching television and videos rather than exercising

Most human beings are predisposed to gain weight when rich food is abundant because, in the past, starvation was all too often a real possibility. Therefore, a tendency to score calories in the form of fat provided a definite survival advantage. We have no counter-mechanism to prevent our bodies from gaining too much weight when all those yummy foods are so available as they are now. When diets are more or less routine and predictable, people habituate to what they are eating and eat less of it. As food become more varied people eat more and gain more weight. In addition, in America, portion sizes have become “gargantuan” according to many Europeans and Asians.

Exercise is another nongenetic influence on weight. Exercise boosts the body’s metabolic rate and may lower its set point. When obese women are put on a severely restricted diet their metabolic rates drop sharply. But when they combine the diet with moderate physical activity, such as daily walking, they lose weight and their metabolic rates rise. This is true even for those who are genetically susceptible to obesity.

Cultural customs and standards of what the ideal body should look like shape eating habits and activity levels. In many places around the world, especially where famine and crop failures are common, fat is taken as a sign of health, affluence in men, and sexual desirability in women. In the United States, African-Americans and Mexican-Americans are much more accepting of fat people than white Americans.

The ironic thing is that despite the overall rise in weights the cultural ideal for white women in the United States, Canada, and Europe has been getting thinner and thinner. Today the female ideal is an odd combination of big breasts and no hips. Pressures for American men to be “buff” and strong have also increased.