How Your Genes Affect Your Diet

Date: January 1, 2017      Publication: Bottom Line Health      Source:  Sharon Moalem, MD, PhD      Print:

Nutrigenetics is uncovering new links…

Have you ever wondered why a cup of coffee keeps you up at night, while your spouse downs cup after cup and sleeps like a baby? Or why a glass of wine with supper makes you tipsy, while your friends can keep sipping for hours?

You could chalk it up to random variation, but it’s actually not random at all. It’s largely determined by your genes. Research has shown that specific genes and gene “variants” (or mutations) can affect how your body metabolizes nutrients and other substances such as caffeine and alcohol.

For certain medical conditions, it’s long been established that there is a genetic link to how specific nutrients are metabolized. For example, if you’re among those of western European ancestry who have different versions of the HFE gene, it can cause you to absorb two to three times more iron than those without this genetic profile. Hereditary hemochromatosis, commonly known as iron overload disease, can be life-threatening—and is diagnosed, in part, with genetic testing.


But new research in the emerging field of nutrigenetics (the study of how individual genes affect nutrition) shows that there may be important genetic links to many more nutrients and substances than previously thought.

So far, scientists have identified hundreds of genes and gene variants that may affect how your body metabolizes different nutrients and substances.

The question is, can knowing this genetic information help people make smarter nutrition choices? Right now, the jury is still out, but some individuals find that testing helps them identify certain dietary tweaks that may improve their overall health. Key nutrients and substances with genetic links…

Folate. Specific versions of the MTHFR gene slow the rate at which the body converts folate into a usable form of the vitamin. People who inherit this gene may be more likely to suffer a heart attack or stroke because of a folate deficiency.

Who might benefit from this test: If you have a personal or family history of heart attack, you may want to discuss this test and/or a blood test for folate deficiency with a nutritionist. If you test positive for the gene and/or a blood test identifies a folate deficiency, ask your doctor about taking a supplement with a methylated (active) form of folate.


Caffeine. The body’s ability to metabolize caffeine is controlled mostly by the CYP1A2 gene. People with a particular variant of this gene are “slow metabolizers”—they don’t have the same ability to break down caffeine as other people. They might develop high blood pressure from drinking amounts of coffee or tea that wouldn’t similarly affect a person without this gene.

Who might benefit from this test: If you have high blood pressure or become jittery when consuming caffeine, you may want to discuss this test with a nutritionist. If you test positive, you would likely benefit from reducing your intake of caffeinated beverages and foods.

Alcohol. Research has found that moderate daily alcohol consumption—up to two alcoholic beverages for men…and up to one for women—can improve cardiovascular health.

But those who have the ALDH2*2 gene might want to disregard this finding. They don’t have the same ability to detoxify an alcohol by-product (acetaldehyde), which increases their risk for a deadly esophageal cancer.  

Who might benefit from this test: Anyone with Asian ancestry…risk factors for esophageal cancer  (such as gastroesophageal reflux disease)…and those who notice their skin becoming red or flushed after drinking alcohol. If you test positive for this gene, avoid alcohol.



A nutritionist or health-care professional (such as a doctor) can order a test kit for nutritional genetic testing online. You provide a saliva sample, and the kit is returned for analysis. The test usually costs a few hundred dollars to check for a set of genes that may have nutritional links. The professional who ordered the test will likely charge you for a follow-up consultation to discuss the results. These fees are unlikely to be covered by insurance.

Self-test for alcohol tolerance

If you’re interested in learning how your genes might affect the way your body metabolizes alcohol, there’s a self-test I have developed based on genetic indicators found in one’s earwax. It is not as accurate as genetic testing but will give you some basic information.

Moderate drinking (described above) is considered good for the heart, but some people (such as many of those who become flushed while drinking) should never drink…and everyone’s alcohol tolerance is highly individualized. How much alcohol (if any) is right for you?

The earwax test. Carefully swab some of your earwax and take a look. People with flaky, dry, gray earwax probably had ancestors from eastern Asia who rarely drank. Those with the wet type of earwax (it’s a yellow/brownish color and is somewhat sticky) typically had African or European ancestors who drank alcoholic beverages routinely.

My advice: If you have dry earwax, the safest approach is for you to avoid alcohol altogether—your genetic profile does not prepare you to safely metabolize alcohol. Also, people in this group are likely to have inherited the gene that predisposes them to squamous cell esophageal cancer. For this reason, it’s wise to forgo alcohol since it is an important risk factor for this type of cancer. If you have wet earwax, you are unlikely to have the same difficulty metabolizing alcohol.


Source: Sharon Moalem, MD, PhD, a physician, scientist and inventor based in New York City. He has served as an associate editor for the Journal of Alzheimer’s Disease and has been awarded more than 25 patents for inventions in the fields of biotechnology and health. He is the author of The DNA Restart: Unlock Your Personal Genetic Code to Eat for Your Genes, Lose Weight and Reverse Aging.