We are all aware that what we eat can have a major impact on our health, but new research by scientists in the U.S. suggests that our genes may influence which type of “healthy” diet will be best for each one of us. “Dietary advice, whether it comes from the U.S. government or some other organization, tends to be based on the theory that there is going to be one diet that will help everyone,” says David Threadgill, Ph.D., at the Texas A&M College of Medicine and College of Veterinary Medicine & Biomedical Sciences. “In the face of the obesity epidemic, it seems like guidelines haven't been effective.”
Dr. Threadgill’s team used four different groups of mouse models to investigate how five different diets affected health over six months. Individual mice within each of the four groups were genetically almost identical, but the genetic differences between each group were roughly the same as those you might find between two different people.
Four of the diets given to the mice were created to be roughly equivalent to popular human diets. One was a western-style diet that was high in fat and refined carbohydrates. The other three human-comparable diets were purportedly “healthier”—a Mediterranean diet with wheat and red wine extract; a Japanese diet with rice and green tea extract; and a ketogenic, or Atkins-like diet, which was high in fat and protein, and very low in carbohydrates. The fifth diet comprised a standard, commercial mouse chow.
“I wanted to get the diets as close to popular human diets as possible,” comments William Barrington, Ph.D., lead author on the study. “We matched fiber content and matched bioactive compounds thought to be important in disease.” The researchers analyzed the animals physical responses to look for any evidence of diet-related metabolic syndrome and evaluated metabolomic and epigenetic alterations associated with dietary response. They also studied any behavioral differences, including how active the animals were, and how much they ate.
What the team found was that not all of the genetically different mouse groups responded the same to each diet. One of the four genetic types fared particularly poorly on the Japanese diet. “The fourth strain, which performed just fine on all of the other diets, did terribly on this diet, with increased fat in the liver and markings of liver damage,” Barrington says.
And while two of the genetic types responded well to the Atkins-like diet, the other two didn’t do so well. “One became very obese, with fatty livers and high cholesterol,” Barrington notes. Another group became less active and developed more body fat, but still remained lean. “This equates to what we call 'skinny-fat' in humans, in which someone looks to be a healthy weight but actually has a high percentage of body fat.”
Perhaps to be expected, none of the mouse strains did well on the American-style diet. Two of the four genetic types became very obese and had signs of metabolic syndrome. Another didn’t show as many negative effects, but did develop more fat in the liver. There was a mixed reaction to the Mediterranean diet, with some groups remaining healthy, while others put on weight, although not as much as mice fed the American diet.
The overall results showed that when it comes to diet, one size definitely doesn’t fit all. “My goal going into this study was to find the optimal diet,” Barrington concludes. “But really what we're finding is that it depends very much on the genetics of the individual and there isn't one diet that is best for everyone.”
The A&M Health Science Center researchers, working with colleagues at Johns Hopkins University, the University of Tennessee, Texas A&M University, and the University of North Carolina, Chapel Hill, report their findings in Genetics, in a paper entitled “Improving Metabolic Health through Precision Dietetics in Mice.”
If genetically defined responses to individual diets also exist in humans, then there may well not be a universally “healthy” eating plan for everyone. “If similar genetic-dependent diet responses exist in humans, then a personalized, or “precision dietetics,” approach to dietary recommendations may yield better health outcomes than the traditional one-size-fits-all approach,” the authors write.
The team aims to continue their work and find out which genes are implicated in dietary response. “One day, we'd love to develop a genetic test that could tell each person the best diet for their own genetic makeup,” Barrington adds. “There might be a geographical difference based on what your ancestors ate, but we just don't know enough to say for sure yet.”