In a study on crab-eating macaques (Macaca fascicularis), a team of researchers at Wake Forest University found that the primates on a humanlike Mediterranean diet chose not to eat all the food available to them and maintained a normal weight; by comparison, the animals on a Western diet ate far more than they needed and gained weight; the study also provided the first experimental evidence that a Mediterranean diet protects against non-alcoholic fatty liver disease (NAFLD) compared with a Western diet.
Shively et al aimed to determine the effects of humanlike Western and Mediterranean diets on caloric intake, obesity, metabolism, and hepatosteatosis in an established nonhuman primate model of obesity. Image credit: Moira Nazzari.
“This is the first preclinical trial to measure the effects of long-term consumption of a Western versus Mediterranean diet on obesity-related diseases under controlled experimental conditions,” said Professor Carol Shively, lead author of the study.
Previous research on the effects of diet type on caloric intake was largely based on human population studies that relied on self-reported food intake, which is often unreliable, or rodent studies with nonhuman-type diets.
The new study was a 38-month (equivalent to about 9 years for humans) prevention trial.
The diets were formulated to closely reflect human diets with protein and fat derived largely from animal sources in the Western diet and primarily from plant sources in the Mediterranean diet. However, the two diets contained comparable proportions of fat, protein and carbohydrates.
There were 38 female crab-eating macaques in the study which were randomized to either the Mediterranean or Western diet.
Both groups were matched on their baseline weight and body fat and were allowed to eat as much as they wanted throughout the study.
“What we found was that the group on the Mediterranean diet actually ate fewer calories, had lower body weight and had less body fat than those on the Western diet,” Professor Shively said.
The Mediterranean diet also protected against NAFLD, which can cause cirrhosis of the liver and liver cancer, and require a transplant. Obesity is a major cause of NAFLD.
“Diet composition is a critically important contributor to the U.S. public health, and unfortunately those at the greatest risk for obesity and related costly chronic diseases also have the poorest quality diets,” Professor Shively said.
“The Western diet was developed and promoted by companies who want us to eat their food, so they make it hyper-palatable, meaning it hits all our buttons so we overconsume.”
“Eating a Mediterranean diet should allow people to enjoy their food and not overeat, which is such a problem in this country.”
“We hope our findings will encourage people to eat healthier foods that are also enjoyable, and improve human health.”
The study appears in the journal Obesity.
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Carol A. Shively et al. Mediterranean versus Western Diet Effects on Caloric Intake, Obesity, Metabolism, and Hepatosteatosis in Nonhuman Primates. Obesity, published online April 23, 2019; doi: 10.1002/oby.22436
