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No Single Food Regimen Works For Everyone, Finds New Study

Cynthia Graber and Nicola Twilley

A decade ago, spurred by the success of the Human Genome Project and the affordability of genetic sequencing, scientists began to explore the promise of “nutrigenomics.” Could personalised nutrition, informed by knowledge of an individual’s DNA, help prevent and even treat diet-related diseases?

The results of early studies were compelling: Genetic differences seemed to predispose individuals to lose different amounts of weight on different types of diets. A multimillion-dollar industry soon sprang up, premised on marketing DNA-based diets. But subsequent research has failed to show any statistically significant difference in weight loss between overweight people who “eat right for their genotype” and those who do not.

Nutritionists have long observed that no one weight-loss strategy works for everyone. What, then, explains the variation in individual metabolism?

Last year, Tim Spector and Sarah Berry, epidemiologists at King’s College, London, and Andrew Chan, of Harvard Medical School, began an ambitious new search for the answer. Their new study, called Predict, is the world’s largest and most comprehensive experiment to look at individual responses to food.

Their preliminary results documented substantial and surprising variations in how well participants processed fats and carbohydrates, even among identical twins. How efficiently a person metabolised one macronutrient was no predictor of how that person might respond to another.

In 1992, Spector set up TwinsUK, a research registry that now includes over 13,000 identical and fraternal twins. Based on the twins, he concluded that genes contributed 70% of an individual’s risk for obesity, on average. He then began a series of studies to tease out which factors influenced the remaining 30%.

His study included 700 identical twins, 300 individual British volunteers and 100 subjects from the US, and gathered data on almost everything that can affect metabolism: gut microbiota, sleep duration, exercise, body fat composition and more.

The team concluded that genes play a limited role in how a person processes fats and carbohydrates. Among identical twins, only half of the amount and duration of an individual’s post-meal blood glucose level could be attributed to genetic influence.

A more detailed view has come only recently, with the advent of machine learning, wearable sensors and genetic sequencing. For one thing, experts say, the basic parameters of a healthy diet are already known: plenty of whole grains, pulses, leafy greens and other vegetables, enough healthy oils and seafood, and little red meat or refined carbohydrates. The problem is not that the guidelines are wrong or insufficiently personalised, but that people are not following them.