First there was precision medicine, then precision health, and now “precision dietetics”. New research into how genetic differences influence health responses to several popular diets found health effects were highly dependent on genetic background, suggesting that a personalized approach to diet might be more effective than the traditional one-size-fits-all guidelines.
Findings from this Texas A&M initiated research were published earlier this month in Genetics.
"Dietary advice, whether it comes from the United States government or some other organization, tends to be based on the theory that there is going to be one diet that will help everyone," said David Threadgill, PhD, with the Texas A&M College of Medicine and College of Veterinary Medicine & Biomedical Sciences, senior author of the study. "In the face of the obesity epidemic, it seems like guidelines haven't been effective."
The researchers used four different groups of animal models to look at how five diets affect health over a six-month period. The team chose the test diets to mirror those eaten by humans—an American-style diet (higher in fat and refined carbs, especially corn); Mediterranean (with wheat and red wine extract); Japanese (with rice and green tea extract); and ketogenic, or Atkins-like (high in fat and protein with very few carbs). The fifth diet was the control group.
One of the four genetic types did very poorly when eating the Japanese-like diet. "The fourth strain, which performed just fine on all of the other diets, did terrible on this diet, with increased fat in the liver and markings of liver damage," said William Barrington, lead author on the study and a recently graduated Ph.D. student from the Threadgill lab.
A similar thing happened with the Atkins-like diet: two genetic types did well, and two did very badly. "One became very obese, with fatty livers and high cholesterol," Barrington said. The other had a reduction in activity level and 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."
"In humans, you see such a wide response to diets," Barrington said. "We wanted to find out, in a controlled way, what was the effect of the genetics." They measured physical signs, especially evidence of metabolic syndrome. They also studied any behavioral differences, from how much they moved around to how much they ate.
The animal models tended not to do great on the American-style diet. A couple of the strains became very obese and had signs of metabolic syndrome. Other strains showed fewer negative effects, with one showing few changes except for having somewhat more fat in the liver. With the Mediterranean diet, there was a mix of effects. Some groups were healthy, while others experienced weight gain, although it was less severe than in the American diet.
The results demonstrated that a diet that makes one individual lean and healthy might have the complete opposite effect on another. "My goal going into this study was to find the optimal diet," Barrington said. "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 research team's future work will focus on determining which genes are involved in the response to the diets. "One day, we'd love to develop a genetic test that could tell each person the best diet for their own genetic makeup," Barrington said. "There might be a geographical difference based on what your ancestors ate, but we just don't know enough to say for sure yet."