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What Personal Genetic Testing Can and Can’t Tell You about Nutrition

Paleo food pyramid

Everyone knows that genetics influences your risk for all kinds of health problems, from Celiac Disease to cancer risk. We’ve already covered some population-wide genetics issues, but we’re living in the age of direct-to-consumer genetic testing, where you can get your very own genes analyzed for a pretty low price, without having to rely on population averages. These tests identify single nucleotide polymorphisms, or small variations in genetic coding. But is all that information really worth knowing?

Sometimes, it can be hard to figure out which genes actually represent (a) a significant risk, that (b) you can do something about. If the risk is really tentative, it might not be worth your worry. If you can’t do anything about it, will it really help to fixate on it?

There is some evidence that a few genetic markers represent significant and modifiable risk factors for various diseases. In other words, these are things that you can do something about, and also that you might have a reason to act on. But for other genes, there isn’t any evidence that people with that gene variation need to do anything specific (you don’t need a genetic test to tell you that avoiding sugar or exercising is good for your health). And genetic testing also has limits.

MTHFR Polymorphisms Might Affect your Supplement Choices

That wasn’t an attempt to slip profanity past any kids who might be reading over your shoulder. MTHFR is an enzyme, and the abbreviation stands for Methylene Tetrahydrofolate Reductase, which is significantly less exciting than the word you probably thought of first.

The MTHFR gene regulates the production of the MTHFR enzyme, which controls metabolism of folate (aka Vitamin B9). It’s also important for your body’s built-in detoxification system. People with certain polymorphisms in the MTHFR gene have elevated blood levels of an amino acid called homocysteine, which can increase the risk of diabetes, certain cancers, high blood pressure, and possibly also dementia. Depending on which polymorphism of the MTHFR gene you have, it can also cause a deficiency in folate and other B vitamins.

MTHFR polymorphisms are incredibly complicated and not well-understood. But this may be one time when a supplement is actually better than food. Instead of getting more dietary folate, this review suggests supplementing with methyltetrahydrofolate, which is a form of folate that’s more easily absorbable for people with MTHFR mutations.

That’s promising when you combine it with this review, which found that MTHFR polymorphisms only affected DNA in people with low levels of folate, and this one, which found that MTHFR affected heart disease risk much more strongly in people with low folate status.

A Few Genes Might Suggest Different Diet Compositions for Weight Loss

Another question that genetic testing might help you answer is that old standby, “How many carbs should I eat?” The answer depends on a lot of things, not just genetics. But some genetic polymorphisms might hint at part of the answer.

AMY1 and Carb Tolerance

When you eat any kind of carbohydrate, digesting that carbohydrate starts with an enzyme called amylase right in your mouth, before you even swallow it. AMY1 is a gene that controls how much amylase you produce in your mouth: the more copies of AMY1 you have, the more amylase you make.

If you’re eating a high-carb diet, AMY1 may protect against obesity. On the other hand, if you have a low number of AMY1 copies, a lower-carb diet might work better for you because your body just doesn’t break down and digest carbohydrates as well.

CLOCK Genes and Dietary Fat

To go completely in the opposite direction, some people actually do better on low-fat (yes, it’s true!) and if you have a polymorphism in the CLOCK gene, you could be one of them.

The CLOCK gene regulates circadian rhythms, and we all know how important circadian rhythms are for weight loss. This study found that people with a polymorphism of the CLOCK gene tended to do better on a low-fat diet than a purely low-calorie diet. Different forms of the CLOCK gene have been associated with obesity and resistance to weight loss before, so the low-fat study is exciting because it might point to a way around that resistance.

APOE Polymorphisms Might Affect your Fat and Cholesterol Choices

One last way that the results of genetic testing might point to a better diet for you: APOE polymorphisms might nudge you towards different choices of fats to consume.

APOE stands for Apolipoprotein E, which is a protein involved in cholesterol metabolism. The gene that controls APOE is called the APOE gene, and it has several different forms. The most notorious form is APOE4, which increases risk of Alzheimer’s Disease, dementia, other aging-related brain problems, sleep apnea, and cardiovascular disease. People with ApoE4 have lower antioxidant activity and higher rates of inflammation – it’s just bad news.

Because these effects are all tied up with cholesterol metabolism, it’s logical to think that you might be able to change them by changing dietary fat and/or cholesterol. But actually, studies on dietary cholesterol have been mixed. If there’s something wrong with the APOE gene (not one of the polymorphisms like APOE4, but an actual malformation), that can cause hypercholesterolemia. But it’s not clear that polymorphisms work the same way. This review covers the role of diet and ApoE4 – reducing fat and cholesterol seems to have an effect, but only in men. On the other hand, this study found that egg and/or cholesterol intake wasn’t associated with an increased risk of heart disease, even in men with the APOE4 gene.

What might help more is increasing dietary Omega-3 fats. Because of the way they metabolize fat, carriers of the APOE4 variant may need more dietary Omega-3 fats to get the health benefits. So if you’re APOE4, you might be able to have a real positive effect on your health by eating more fish.

Limitations and Drawbacks

Now time for the bucket of cold water.

Sleepless man

“Well, my FTO polymorphism suggests that I might be prone to obesity…but hey wait, I already knew that from 20 years of unsuccessfully trying to lose weight!”

A lot of “disease-related” genes tell you nothing you didn’t already know. Just for example, say you have a gene that makes you more susceptible to Type 2 Diabetes. The logical response is to take up diet and lifestyle habits that are protective against Type 2 Diabetes, like regular exercise and a diet low in sugar and refined carbs…but almost everyone in the world could benefit from regular exercise and a diet low in sugar. You didn’t need a genetic test to tell you that!

Or take the most infamous obesity-related gene of them all, the FTO gene. Polymorphisms in the FTO gene have been associated with obesity, but it’s not clear what (if any) diet helps reduce those effects. So just knowing you have the FTO gene tells you nothing useful, because it doesn’t give you any information you can act on. The same goes for the differences in the PPARG gene. And in fact, some studies question whether any of these polymorphisms have real-world effects on real people.

Also, most risk factors identified on genetic tests add a very small amount of total risk. To stick with FTO, polymorphisms on the FTO gene explain 0.31% (0.0031) of BMI variation. That’s tiny. It’s definitely not destiny.

Finally, and this is important: do some digging into the company you use. You might assume they’ll keep your information private. But do you know? Have you read the privacy policy? You’re literally entrusting this company with your DNA; it’s worth 20 minutes of your time to figure out what they’re going to do with it.

The Bottom Line

This stuff is kind of cool, in an information-nerd kind of way. But it’s just not clear how much it can actually tell you that you didn’t already know. So you took a genetic test and it told you that you’re at a higher risk of obesity, so you decide to eat an anti-inflammatory diet and really work on your sleep quality to improve your health. Great, but you could have just cut out the genetic testing because regardless of what genes you have, your body will thank you for eating an anti-inflammatory diet and getting enough sleep.

A few genes, like AMY1 and MTHFR, already tentatively point to some specific recommendations. In 4 or 5 years, we might start seeing really personalized recommendations that are specific to particular genes. But right now, it might not be helpful at all for the average person to get a genetic test, because it’s just not clear how much actionable information is really gives you.