Genes affect weight gain from fatty diets

Genes play a role in weight gain resulting from diets high in fat and sugar content, say scientists. The study in mice looked at over 100 genetically different breeds and how their bodies responded to high-fat, high-sugar diets. Researchers found eleven regions within the genome that were associated with fat gain and obesity - some of which corresponded to areas of the human genome that are also linked to obesity.

'We found that obesity has similar genetic signatures in mice and humans, indicating the mice are a highly relevant model system to study obesity. Overall, our work has broad implications concerning the genetic nature of obesity and weight gain', said Dr Brian Parks of the University of California, Los Angeles, who was involved in the study.

The study began with mice receiving a normal diet for eight weeks, followed by a high-sugar or high-fat diet for eight weeks - the latter replicating a typical fast-food diet. Scientists assessed the changes that resulted from the altered diet, including the deposition of fat, changes in normal gut bacteria and gene expression. Although the mice received the same diets, their responses varied depending on their genetic make-up, with some mice not showing any increase in body fat and others showing an increase of over 600 percent.

Professor Jake Lusis, who led the study at the University of California, Los Angeles, said to TIME: 'People generally assume that obese people eat a lot, but it was surprising that the weight gain [in mice] wasn't determined by the amount of fast-food that was consumed'.

By looking at the changes in gene expression that occurred alongside fat gain, the scientists suggest that approximately 80 percent of body fat is regulated by genes. The results indicated that the amount of food consumed did not necessarily equate to the amount of body fat the mice gained, and that the genetic control of their physiology was a significant contributor.

'Our study suggests that what's more important is their physical activity, how much the mice move and how some metabolise food. Some are more efficient at taking calories and putting them into fat rather than just spending it as energy. In the case of the mice, it looks like the metabolism and activity is way more important than the amount of food consumed', said Professor Lusis to TIME.

Future work will focus on investigating how the genetic regions identified specifically contribute to fat gain and obesity. Professor Lusis concludes: 'Genes don't act individually, they act by affecting other genes and interacting with the environment. If we can understand the full picture, it could potentially be really important for the critical problem of obesity'.