DNA and Your Diet

Ancestry.com, 23andMe, Genebase, and many more companies will send you a kit that lets you take a DNA sample and mail it in. In return, they send you an estimate of your ancestry showing where your forebears lived and, depending on the company, a variety of other information. You might discover that your sweet tooth is hereditary, that your earliest ancestors farmed the steppes of Central Asia, or that you have first cousins nearby. Can this information also give you important insights into DNA and your diet?

More than 20% of Americans have taken a mail-in DNA test. The results can be downloaded and shared with companies promising to provide personalized recommendations of the best food choices for you. Is there value to this, or is it just a fad?

Genetic food questions

Some things about human dietary needs are just generally true. As Ronnie Chieng puts it, “Are you Irish? Eat more vegetables! Are you Chinese? Eat more vegetables!” All of us should eat mostly fruits and vegetables, whole grains, and lean protein.

But there are genetic differences. One well-known example is lactose intolerance. Lactose intolerance is an inability to digest lactose, a protein found in milk. According to research from the National Institutes of Health, 98% of people from Vietnam are lactose intolerant, while only 4% of people from Denmark are.

If your ethnic heritage is mostly from Denmark, you might be wise to include dairy foods in your diet. If your family came mostly from Vietnam, you should consider getting calcium from other sources. 

Much of the recent research in nutrigenomics does not translate into clear-cut advice like this. For example, women who are at a relatively low genetic risk for obesity may end up with less abdominal fat when they eat higher levels of polyunsaturated fat — but this doesn’t necessarily tell anyone that she needs to eat more walnuts.

Bold claims

Companies offering personalized advice on DNA and your diet are making stronger claims than these. “Discover your own DNA diet,” one company says. “An ideal combination of macronutrients, protein, carbohydrates, and healthy fats designed specifically for your genetics.” 

But what are they offering? A report from one of these companies made a fairly vague suggestion that the subject had “high need” for most vitamins. 

Another company identifies DNA links with a tendency toward higher or lower levels of vitamins. They admit that levels of micronutrients are “mostly influenced by the foods you eat.”

Other companies mention “high sensitivity” to carbohydrates. There is some research suggesting  that some genetic differences affect how some populations metabolize refined carbohydrates. For example, the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene may contribute to liver fat when people who have this gene eat lots of sugar.

However, there is no indication that eating lots of sugar is good for anyone. The advice for people with high sensitivity to carbohydrates is to have balanced meals that focus on complex carbohydrates. This is good advice for anyone.

The Harvard School of Public Medicine also makes the point that nutritional studies of geographic groups can’t usually distinguish between how an ethnic population is genetically programmed to handle specific foods and how the economic and cultural realities of a country affect the residents’ nutrition.

Do DNA diets work?

Advice in these pricey DNA diet plans tends to be, like horoscopes, very broad and vague. Diet plans, recipes, and grocery lists may be included, but the diet they are built around tends to be similar to the Mediterranean diet or other popular balanced diets. 

The Academy of Nutrition and Dietetics says that “the practical application of nutritional genomics for complex chronic disease is an emerging science and the use of nutrigenetic testing to provide dietary advice is not ready for routine dietetics practice.”

If you want to try out a DNA diet plan and you think the novelty could help you follow through, consider discussing it with your family doctor to make sure that the specific plan you receive is actually a good choice — for you or for anyone.