Several of you have written asking me to revisit the subject of nutrigenomics, which is the attempt to use genetic testing as a way to steer dietary recommendations.

Nutrition Diva listener Brad writes:

You did an episode on DNA-based diets in 2012 (episode 203). I know the genetics field is changing very quickly and I was hoping you could revisit this subject. Some of the companies who do the testing also sell specific supplements based on your results, which seems a little suspcious. What is the state of the art?

Another listener, Dizz, wrote:   

I keep seeing these DNA testing companies on social media. They claim to have studies on their website supporting their results. I haven’t actually done the test, but I read a sample report and it seemed like the recommendations (like eat a high fiber diet) were just common sense and would apply to everyone. Can you hang your hat on these tests?

If you've been wondering whether DNA testing can help you zero in on the best diet, there's new research out that I think you’ll find quite interesting.

No Single Diet Works Best for Everyone

Since the sequencing of the human gemone, there's been a lot of interest in nutrigenomics. It’s long been clear that we don’t all respond the same way to the same dietary interventions. Some people do really well on a higher fat diet. Others develop high triglycerides or cholesterol on the same diet. Some people lose more weight when they reduce carbs. Others lose more weight when they increase complex carbs and reduce fat.  

If these differences are genetic, maybe we could skip some of the trial-and-error and zero in on the best approach for each unique individual based on their DNA.

Now that inexpensive mail-order genetic testing is available, companies have started selling personalized nutrition programs that are supposedly based on your DNA. When I talked about this back in 2012, we didn't have any research to show that these DNA-driven diets are any more effective or valid than standard dietary recommendations. We also didn't have evidence that DNA-driven supplement regimens prevent disease. 

Last year, a team of researchers from Kings College in London and Harvard Medical School launched an ambitious research project, called the PREDICT study, to figure out what factors determine an individual’s unique response to food. The study included 700 identical twins along with 400 non-twins. It evaluated, among other things, the rise and fall in blood sugar and blood fats after eating various kinds of food. These responses could shed light on which diets would be most effective in preventing diabetes or heart disease for a given individual.

Do Our Genes Determine Our Response to Diet?

Preliminary results from the PREDICT study, which were presented at the 2019 meeting of the American Society of Nutrition, confirm what we’ve already observed: Different people respond very differently to the same dietary inputs. There is no one dietary approach that’s going to work best for everyone. 

If these differences are genetically driven, then we would expect the identical twins to respond similarly. But they didn’t. Genetics appeared to account for less than a third of the subjects’ insulin and triglyceride responses. The specific ratio of fats and carbohydrates in the diet were also not strongly predictive. Other factors, such as sleep habits, exercise, stress, and gut microbes appeared to play a much bigger role in our individual responses to diet.

This is bad news for companies who are selling DNA-based diets. But it’s good news for you and me. We can’t change our genes. But we can change how much we sleep, how we manage stress, and how much we exercise. We can even influence our gut microbes.

Eat Your Vegetables (No Matter What Your Genotype)

On the one hand, the principle components of a healthy diet and lifestyle are pretty universal. Everyone is going to benefit from eating more whole foods, avoiding excessive sugar, alcohol, and processed food, getting enough sleep, and moving their bodies.

On the other hand, the more I can help you tailor your diet and habits to fit your individual needs, preferences, and lifestyle, the better and more sustainable your results will be.

So, I’m not arguing against personalized nutrition, I’m just saying that, at present, it doesn’t look like DNA testing is the most useful approach. Our best tool is still to observe how your body responds to a given approach and adjust based on your results.

I have a good friend who has a genetic predisposition to diabetes. DNA testing would probably advise him to follow a low carb diet, which he did for many years. During that time his blood sugar rose steadily until his doctor threatened to put him on blood-sugar-lowering medications. Instead, he decided to try something different. For him, it turned out that a plant-based diet (which is much higher in carbohydrates) was much more effective in controlling his weight and his blood sugar.  

Your doctor can monitor things like your cholesterol and blood sugar levels. But between visits, you have access to a lot of other information. Is your weight trending up, down, or staying steady? How are your hunger levels, energy, and stamina? If you’re not happy with the status quo, make some changes and observe what happens. No DNA testing required.

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