As children, Helen Sparre and Sarah Guy appeared identical in both face and figure; a pattern which continued into their twenties – when both twins were underweight – and into their thirties and early forties, when they began to gain some additional pounds. Yet, according to a new study, in which they participated, these similarities are only skin-deep: Just 50 per cent of our response to glucose, and less than 20 per cent of our response to dietary fats is genetic, meaning that even identical twins respond very differently to the same meal.
“Everyone is unique in their food response, which may help explain why one-size-fits-all dietary guidelines often fail,” says Tim Spector at King’s College London who led the study. He is now developing an app which could ultimately predict the healthiest food choices for any given individual, following a test.
The team found that, whereas some people experienced a rapid and prolonged increase in blood sugar and insulin in response to a given meal, such as a high-fat or high-carb muffin, others responded to the same meal with a large and sustained increase in the amount of fat circulating in their bloodstream. The first of these responses is a pattern associated with an increased risk of weight gain and type 2 diabetes, whereas the second is associated with an increased risk of cardiovascular disease.
Surprisingly, these differences were also observed in twins sharing identical DNA sequences. For instance, in response to a sugary drink, one twin had more than double the spike in blood glucose of their identical twin – a pattern also observed when they consumed a standard muffin. But when they consumed a high fibre muffin, their responses were more similar.
“It shows us that our environment is also important to our response to food,” says Isabel Garcia-Perez at the Centre for Translational Nutrition and Food Research at Imperial College London.
One possible explanation for these differences, is variation in the participants’ gut microbiota. In the study, identical twins were found to share just 37 per cent of the same gut microbes; in unrelated individuals it was 35 per cent. Variability in people’s sleep, circadian rhythms, or exercise could also explain the differences, says Spector, who presented the results at the American Diabetes Association conference in San Francisco this week.
The team are using the data from the study to try to build a system that can predict how people would respond to untested foods. So far, the system can predict glucose responses with 73 per cent accuracy.
The team plan to release an app next year, which will be used to gather more data from individuals, and which they hope could ultimately advise them on the healthiest food choices based on their responses to a test meal, or series of meals.
“This is a massive and unprecedented effort to identify the predictors of people’s response to caloric and nutrient intake, and it is an approach has the potential to tell us a lot,” says Claude Bouchard at Pennington Biomedical Research Center in Louisiana.
Even so, recent studies suggest the metabolic fate of a meal can also be influenced by what we consumed the day before – something they haven’t necessarily accounted for in this study, he says.
As for Sarah and Helen, the message they’ve taken from participating in the study is that, although they may look identical, their responses to foods are very different: Sarah has an ‘unhealthy’ metabolic response to chocolate, but Helen tolerates it well – whereas she has an ‘unhealthy’ response to potato crisps, which isn’t shared by her twin.
“It’s funny because when we were little, we always used to say that if you put the two of us together, you’d have one person,” says Sarah, “and that’s what these results appear to be showing as well.”