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There is a growing pile of evidence showing that obesity is not just a result of bad eating habits, but is a result of a variety of factors such as behavior, environmental factors and genetics. The interaction of these factors is more likely to explain why people gain weight over time rather than a result of just one cause such as poor diet or unhealthy lifestyle.
Claude Bouchard, who is chairman of genetics and nutrition at the Human Genomics Laboratory of Pennington Biomedical Research Center, in Baton Rouge, cites, for example, that while poor dietary habits and lack of physical activity are major factors driving the obesity epidemic, their effects are not the same in everyone.
He says that the body has a biology driver, in the form of pro-obesity genes, which may enhance the risk of behaviors in causing obesity. This is why some people can eat high-calorie foods and not seem to gain weight while others immediately see a significant change in their body measurements. One study that was published in the journal BMJ in 2014 involved more than 37,000 participants and examined the effects of having genetic risks and the frequency of their consumption of fried food. After analyzing the data, researchers found that compared to people with low genetic risk, eating fried food on most days of the week had a greater effect on body size for participants who had a higher genetic risk of obesity. However, some studies also show that a healthy lifestyle can counteract these genetic risks, as seen in people who carry the so-called "obesity genes", but do not become overweight.
How Genes Influence Weight
There are several theories on how your genes may affect your weight.
Fat Distribution. The common belief is that fat distribution differs according to your gender suggests that men typically store fat in their abdomen while women have more fat in the thighs and hips. However, it has been observed that with age, both men and women lose muscle weight, but women tend to store more fat in the abdomen.
Energy Metabolism. Another way your genes may affect your body weight is their effect on how you burn calories. Differences in energy metabolism or how people use calories can determine whether they store excess calories as fat or burn them more efficiently. In one study, UCLA researchers found that mice of different genetic strains which were fed the same normal diet for eight weeks, then fed a high-sugar, high-fat diet for the next eight weeks gained weight in different degrees. While some mice did not have a significant change in body-fat percentage, other mice increased their body fat percentages by up to 600 percent. The scientists explained that those differences may be attributed to genes associated with fat gain and obesity in the mice. They added that many of these genes overlap with those linked to obesity in man. The genetic differences were significant because they affected how some mice were naturally more active and more effective in burning calories while others were not.