Diet Recommendations Based on DNA

Diet recommendations based on DNA are not based on good science.

When the human genome was first sequenced, some people optimistically assumed that we now knew (or soon would know) everything about human genetics and would be able to predict who would develop a disease and prescribe what each individual should do to ensure the best possible health. Those expectations did not pan out. Science is complicated.

Recently several companies have been offering to examine your genome and figure out what you should eat based on your DNA. GenoPalate is a typical one. It promises to tell you:

  • Your optimal macronutrient mix to set the foundation for a healthy diet
  • What amount of each micronutrient your body may benefit from the most
  • Which 100+ foods are the best match for your nutritional needs
  • how your body reacts to substances including alcohol, gluten, caffeine, lactose
  • How to make decisions at the grocery store, for instance whether to buy Brussels sprouts or broccoli

Under the “Our Science” tab they list 10 studies as examples of those they relied on to make their recommendations. That may look “sciency” and impressive at first glance, but most of the studies were inconclusive, preliminary, or not pertinent to the company’s claims. One thing glaringly missing is any study testing whether people who follow the company’s DNA-based diet recommendations are healthier in any way than people who follow standard evidence-based guidelines for a healthy diet.

When one woman’s DNA-based diet and exercise recommendations arrived, she was underwhelmed.

Even though they were ‘personalized’ based on her DNA, they seemed vague and not very actionable. For example, the assessment indicated a ‘high sensitivity’ to carbohydrates. ‘The genes in this panel impact the way you metabolize and assimilate refined carbohydrates, and the combined effect of your variants puts you with a slightly increased effect, meaning you are less well placed to deal with excess carbohydrate intake than most,’ her report read.
According to researchers, there’s a reason why the ‘personalized’ DNA diet plans touted by these wellness companies are filled with generalized scientific jargon and loose recommendations that come with no promises: There’s just not enough evidence yet for truly personalized gene-based diet plans.

Some things to keep in mind:

  • The foods we eat are complex mixtures of ingredients.
  • Genetics is even more complicated.
  • Genes are influenced by other genes.
  • Genes can be turned on or off by other genes and environmental factors.
  • An association between a genetic variant and a disease in a population doesn’t mean an individual with that variant will get that disease.
  • DNA can be wrong; it may predict that a person with brown eyes should have blue eyes.
  • Different companies often provide different DNA-based diet recommendations.
  • Identical twins may have different responses to the same foods.

These companies are mixing half-baked insights from genetic research with standard nutrition and lifestyle guidelines that are available elsewhere for free. The companies charge anywhere from hundreds to thousands of dollars.

Conclusion: Not based on good science

Are you sick and tired of people who tell you what to do and what to eat? I know I am! They all disagree with each other and they don’t offer credible scientific evidence. As for me, I’ll continue to eat a variety of foods that taste good, and to follow the general advice of nutrition experts who agree with each other about the existing science.
One of the first things I looked into, working with Stephen Barrett on Quackwatch, was dubious genetic testing. We quoted an expert whose words are just as true today as they were back in 2008:

For most people, tailoring your diet to your genetic make-up is about as scientific as tailoring your diet to your star sign.

This article was originally published in the Science-Based Medicine Blog.

Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine Blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.

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