People have unique biological responses to food, to a degree that calls into question the usefulness of generalized dietary guidelines, according to a new study.

The study was coordinated by ZOE, a nutritional research company, and conducted by researchers from Kings College London and Massachusetts General Hospital. It examined the effects that specific meals had on the bodies of 1,100 test subjects over two weeks. about 60% of these were twins, removing genetic differences as a factor.

Researchers found that the subjects varied widely in terms of how blood sugar, insulin, triglycerides (fat levels) and other blood markers changed in response to specific meals. Some subjects had spikes that lasted for hours, while others returned to normal quickly. Even identical twins had significantly different responses to the same food.

The amount of fat, protein and carbohydrates present in a given meal accounted for only 40% of the differences in blood-marker changes between individuals. Other factors include the time of consumption, exercise and the composition of intestinal microflora. Regarding the last, the study found that identical twins shared only 37% of their gut microbes, while unrelated individuals shared 35%.

The results imply that, to be effective, dietary advice has to be tailored to the individual to a greater degree than previously thought, researchers say.

The study “underscores that our metabolism is not fixed – we have the power to change it,” said Dr. Andrew Chan, a gastroenterologist at Massachusetts General Hospital. “One exciting avenue is to tailor our diets to the bacteria in our gut that helps us metabolize nutrients.”

The study was presented at conferences of the American Society of Nutrition and the American Diabetes Association but has not yet been published in a peer-reviewed journal. Its subjects were derived from a “TwinsUK study” of 14,000 twins that examined the causes of a variety of chronic conditions. Researchers plan to continue the nutritional study with 1,000 volunteers across the U.S.

By Pan Demetrakakes, Senior Editor