Same diet, different genes, differing levels of success

As obesity rates continue to rise across America, the call to lose weight is becoming ever louder.

Of course, the secret to dieting is to burn off more calories than you consume, but exactly how an individual chooses to go about this has become a complex decision.

The options available to a would-be dieter are nothing short of bewildering.

It is common knowledge that some people seem to respond to one particular diet better than others; what produces good results in one person may have little or no effect in another.

A team of researchers from North Carolina State University set out to investigate this effect in a little more detail. They wanted to see whether individual differences in genetics could impact the effect of specific diets on weight gain or loss.

William Barrington, Ph.D., headed up the research team. Their findings will be presented this Friday at the Allied Genetics Conference, a meeting hosted by the Genetics Society of America.

The research was carried out on mice. According to Barrington, mice offer a good model for the study of dietary changes because their susceptibilities to obesity and metabolic conditions are similar to those in humans.

“There is an overgeneralization of health benefits or risks tied to certain diets. Our study showed that the impact of the diet is likely dependent on the genetic composition of the individual eating the diet, meaning that different individuals have different optimal diets.”

William Barrington, Ph.D.

Four strains of mice were used, and all of the individual mice in each of the strains had the same genetics. In this way, specific diets could be trailed on four genetic types, and the differences between each strain’s response to the diet could be measured.

For 6 months, the mice received food equivalent to various popular diets: a standard Western-type diet, a Japanese menu, the Mediterranean diet, and a high fat, low carb Atkin’s-style (ketogenic) diet. Other mice were fed standard mouse food as a control.

The animals were allowed to eat as much of the food as they wished, and the investigators measured their intake.

Each diet was matched carefully with the equivalent human diet. For instance, the Japanese diet included rice as its main carbohydrate source and featured green tea extract. The Mediterranean diet was supplemented with red wine extract.

Genetic differences in the effects of specific diets

Various health parameters were measured to observe how each diet affected the mice. They found that, overall, the Western diet had negative outcomes, including fatty liver disease and obesity. But, they also noted that the effects of each diet were significantly different, depending on the strain of mouse.

One strain, for instance, seemed to show no ill effects at all from the Western diet.

In another example, the Western and ketogenic diets, both high in fats, had polar opposite effects in two strains of mice. One strain showed negative outcomes from the Western diet, yet displayed no detrimental effects from the ketogenic diet. Another of the strains showed the reverse; they developed obesity and fatty liver disease on the ketogenic diet but were unaffected by the Western-style diet.

Across all strains of mice, the ketogenic diet caused the animals to burn off more calories without increasing their activity levels, but some mice ate so much that they still managed to become obese.

“We also found that the causes for obesity were different. Some mice on specific diets simply ate more calories, and this caused them to become obese. However, mice on other diets ate less but still became obese.”

William Barrington, Ph.D.

Because mice respond in a similar way to nutrition and diet as humans, the researchers believe that there is a high chance that these results are relevant to people. Barrington says: “Since there are different optimal diets for different individuals, this underscores the need for precision nutrition, which would identify optimal dietary patterns for each person.”

The findings have implications for anyone seeking to eat the healthiest diet for them. More broadly, they also bring into question recommendations from official bodies, such as the United States Food and Drug Administration (FDA). Their advice is based on average responses to specific diets and ignores individual differences.

The next step for the team is to try and pin down the genes responsible for the differences in reaction to dietary changes. In the future, they hope that their findings will lead to tests that will allow individuals to identify which type of diet is best for them.

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