Most of us have received public health messages about the importance of eating more plant foods, minimizing ultra-processed foods, and moderating our portion sizes. But beyond a healthy plant-forward pattern, is there one, true diet for humans? On an individual level, how can we best find out which foods we should eat more of or avoid altogether? It might seem that the answer would lie in our DNA. But nutrigenomics – the field that examines the interplay of human nutrition and our genes – is still in the process of reaching that conclusion.
The desire to connect our diets to our ancestors makes sense: Our incredibly adaptable species has permanently settled on every continent except Antarctica. When it comes to what humans can eat, that diversity of environments has produced myriad diets that have enabled us to survive, and even generated genetic adaptations. For example, the practice of raising animals for milk in Northern Europe, India, Africa, and the Middle East is connected to the emergence of genes for lactose tolerance. This ability to drink milk into adulthood emerged as recently as 5,000 years ago. Still, an estimated 65-75 percent of us around the world become lactose intolerant as adults.
In the Arctic, extreme environmental pressure to survive has produced differences in metabolism among the Inuit. Changes to the genes FADS and CPT1A have helped the Inuit metabolize a high-fat diet of fish and marine mammals. East Asian populations in China, Japan, and Korea have also been found to have a variety of unique genetic differences, called polymorphisms, related to blood glucose regulation, and other aspects of metabolism. This is possibly an adaptation to eating a diet high in grains for many thousands of years.
If our genes provide a record of our ancestors’ adaptations to foods, then it would be reasonable to expect great promise from genetic testing to show us what we metabolize best. However, even in a seemingly straightforward case such as lactose intolerance, genetic testing isn’t enough to answer the question, “should I drink milk?” Currently, lactose intolerance is diagnosed with breath testing and almost never with genetics.
When investigating more complex questions, such as which diet someone should follow to prevent heart disease, studies of genes haven’t yet shown us the answer. Earlier this year, an analysis of 29 studies of the interplay between genes, diet, and heart disease found no consensus so far. Particularly contradictory findings surround the influence of genes on our ability to metabolize alcohol and potentially protect us from heart disease.
“Genetic testing for diets tends to be discordant, which puts this type of test in the realm of recreation rather than medicine.”
Direct-to-consumer nutrigenomic testing is already available, promising to tell us what our genes want us to eat. As anyone who has tried more than one of these tests will tell you, sending your genetic samples to different companies will return different, and often directly conflicting, results. Multiple published studies have confirmed that genetic testing for diets tends to be discordant, which puts this type of test in the realm of recreation rather than medicine for now.
The search for proof in nutrigenomics continues. It may be that genes are only relevant to the diets of a small group of people with rare genetic differences. It may also be that other factors, such as the microbiome or our environment, have a larger effect on our health and longevity than single genes that help metabolize our carbohydrates or B-vitamins.
We are still in great need of large-scale clinical trials that will examine health outcomes and help us prescribe diets based on our genes. Massive studies are underway at the NIH that will help make this information available to all in the next 3-5 years. In the meantime, don’t fall for tests that claim to be able to tell you what to eat by testing your genes.