New research may explain why particular diets may help some people to lose a lot of weight, and others only very little. The study, in mice, found that diet response is highly individualized, dependent on genetic makeup.

Researchers fed groups of mice four different diets: a Western diet, a traditional Japanese diet, a traditional Mediterranian diet, or a high fat, low carb Atkins-like diet, also known as ketogenic. "This study used four types of inbred mouse strains. In each strain, every mouse is genetically identical (equivalent to identical twins in people). Using an inbred mouse strain allows us to test multiple diets in individuals with the same genetics. Then, we can compare the effects of the same diets in multiple strains to determine how the individuals’ genetics impact their response to the diet. The genetic diversity between two strains is similar to that between to unrelated people, so our four strains mimic four people in a population," William Barrington, Ph.D., a researcher from North Carolina State University who conducted this study, told ALN exclusively.

Responses to the different diets was highly dependent on the strain of mice used. Most mice fed Western diets gained weight, developed fatty liver disease, and had raised cholesterol. However, one strain of mice showed few to no detrimental effects as a result of this diet.

In fact, two strains showed opposite reactions to the two high fat diets, the Western diet and the ketogenic diet. One strain reacted negatively to the Western diet, showing increased obesity and fatty liver disease, but no negative health effects when fed the ketogenic diet. The opposite was seen in a different strain--they gained weight on the ketogenic diet, but were healthier on the Western diet.

"The mechanism of weight gain also differed by diet and genetics. Some mice simply ate more calories which caused obesity. Others actually ate less but still gained fat," Barrington added.

The results of this study may mean that dietary recommendations, such as the ones issues by the U.S. Food and Drug Administration need to change. Since these recommendations are based upon the average response of the general public, they may not be helpful for each individual. "Currently nutritional guidelines are based on the theory that all individuals respond similarly to diets. We have found this is not the case. Therefore, it is important to develop individualized diets based on genetics in order to promote optimal health in each individual," he said.

"Mice and humans have closely related genetics and have similar propensities to developing obesity and metabolic syndrome," Barrington concluded. "It is highly likely that people will also vary widely in the health effects from a given diet. In the future, we should be able to determine optimal diets for individuals based on their genetics."

This study was presented at The Allied Genetics Conference, a meeting hosted by the Genetics Society of America, held July 13-17 in Orlando, FL.