Identical twins have different responses to the same food

The first results from the largest ongoing scientific nutrition study of its kind suggest that individual responses to the same foods are unique, even between identical twins. Researchers—led by an international team of leading scientists including researchers from King’s College London, Massachusetts General Hospital, and nutritional science company ZOE— presented their findings at the American Society of Nutrition and the American Diabetes Association conferences.

For the study, the researchers monitored 1,100 UK and U.S. adults (60% twins) for blood sugar, insulin, fat levels (triglycerides), and other blood markers in response to a combination of standardized and freely chosen meals over two weeks. The study included a full supervised day in the hospital with regular blood draws and wearable devices to capture sleep and exercise. Individuals also logged their food intake, hunger, and medication in an app, in addition to other clinical investigations such as gut microbe analysis.

The results revealed a wide variation in blood responses to the same meals, whether they contained carbohydrates or fat. For example, some participants had rapid and prolonged increases in blood sugar and insulin, which are linked to weight gain and diabetes. Others had fat levels that peaked and lingered in the bloodstream hours after a meal, raising the risk of developing heart disease.

This large variation is only partly explained by genetic factors (less than 50% for glucose, less than 30% for insulin, and less than 20% for triglycerides) and there is only a weak correlation between an individual’s responses to fat and carbohydrates.

Identical twins who share all their genes and most of their environment often had different responses to identical foods. The study also found that identical twins shared just 37% of their gut microbes—only slightly higher than the 35% shared between two unrelated individuals.

Surprisingly, the proportions of nutrients such as fat, proteins, and carbohydrates listed on food labels explain less than 40% of the differences between individuals’ nutritional responses to meals with similar amounts of calories. There are also large differences in responses to the same meals depending on the time of day they are eaten.

The results suggest that personal differences in metabolism due to factors such as the gut microbiome, meal timing, and exercise are just as important as the nutritional composition of foods, supporting the idea that simple nutritional labeling is insufficient for assessing food.

“For the first time, we’re expanding large-scale nutritional research beyond blood sugar,” said Sarah Berry, associate professor in nutritional sciences at King’s College London and scientific advisor at Zoe. “These findings show that the responses to food of a number of key metabolic markers—including triglycerides, insulin, and blood sugar—are highly individualized. No one has been able to combine data on this scale before.”