I can drink dairy milk with impunity. I can eat all the saturated fat I want without gaining extra weight, although it would probably clog my arteries. And I have at least some of the muscle power of an elite athlete, even if I haven’t made good on that genetic promise.
Genetic tests promising to help you guide your diet and lifestyle are becoming widely available. Thousands of Americans bought them as holiday presents over the winter, and some are now being marketed as the perfect Father’s Day gift.
But what can they really deliver?
To report this story, I took four of the tests on the market, sold by 23andMe, Vitagene, Helix and Orig3n. I can only report on the results from 23andMe and Vitagene; Helix and Orig3n say they lost my results.
DNA tests can tell people if they have rare genetic conditions or if their children risk developing certain diseases, such as cystic fibrosis. But genetic experts say these tests really can’t tell people much of use when it comes to day-to-day living. They’re just not that precise yet.
That's because dozens or even hundreds of genes contribute to traits such as eye color, hair color and height. The risk of heart disease, cancer, and your propensity to gain weight, are even more complicated. There’s no such thing as a single “fat gene.”
Last February, a team at Stanford University found that genes cannot predict who might lose more weight on certain diets.
“It’s not definitive,” says Larry Brody of the National Human Genome Research Institute (NHGRI), one of the National Institutes of Health.
Brody said there are good genetic tests for telling if a person will be helped by a certain drug. One panel of tests can show whether a breast cancer patient needs chemotherapy, for example.
“Where we are still in a gray area is health and lifestyle,” Brody said.
No test can tell you if you eat fewer carbohydrates, you’ll lose weight, or if you do a certain type of exercise you’ll flatten your belly. Human genetics just are not that simple.
Nonetheless, some genetic testing companies tell consumers that they can tailor a diet, supplements and other advice to their genes. I took several of these tests to compare notes on what they found.
There were a few surprises. First, the good.
DNA testing company 23andMe provides a comprehensive, science-based test. To its credit, this pioneer of direct-to-consumer genetic testing doesn’t make promises that don’t hold water.
It does not claim to tell you what to eat or how much to exercise, and provides a huge amount of medical information as a bonus. I was happy to learn I don’t have common genes that predispose to breast cancer, Alzheimer’s or serious genetic diseases such as thalassemia.
One piece of diet guidance the company does offer is on eating saturated fat.
“Some people are likely to gain more weight than others when they eat a high-saturated-fat diet,” said Alisa Lehman, senior product scientist at 23andMe.
I am not one of them, the test tells me. But Lehman, and my detailed 23andMe report, both advise me to take it easy on saturated fat anyway. This fat, found in some meats, cheese and palm oil, can help clog arteries, raising blood pressure and the risk of stroke and heart attack.
“It’s not the whole story, but it’s a piece of the story."
“Limit your saturated fat intake. It may not have a large effect on your weight, but it’s important for reducing your risk of heart disease,” the 23andMe report advises.
“This is one result that may prompt people to take action that they otherwise would not have,” said Lehman.
“It’s not the whole story, but it’s a piece of the story,” she added.
Unlike some of the other companies, 23andMe provides a detailed explanation of which stretch of DNA is involved, with references to the original reports in scientific journals. “This variant is near a gene called APOA2, which contains instructions for making a protein called apolipoprotein A-II,” the report reads.
A rival company, Vitagene, tells me something similar. “You may lose less fat in response to a low-fat diet compared to others,” my Vitagene report reads.
But Chris Longyne of Vitagene’s customer support team cannot tell me any more than that.
“We don’t provide the exact genetic markers for each bit that’s in the report,” he said. “We are obviously trying to make it so people can understand it.”
Both companies also tell me some things I already know. For instance, I carry the Northern European genetic adaptation that allows adults to drink cow’s milk without digestive upset.
But they disagree on caffeine. Vitagene’s test advises that I am a slow caffeine metabolizer, which suggests that I should go easy on the caffeine because it stays in my system longer. It does not explain this finding.
The report from 23andMe says, however, that I carry two genetic variants that make me likely to drink more coffee than average. (It’s true — I do). It names the genes involved: CYP1A2 and AHR, and links to two scientific studies that made the findings.
While this is a fun fact to know about yourself, there's not much the average person can really do with this information.
Vitagene also tells me I am likely to metabolize carbohydrates slowly. Again, it doesn’t explain this finding. A quick search shows there are dozens of genes involved in metabolizing sugars, all through various pathways, so it’s not clear how tests looking at one or two of them might say anything about how an individual’s body might process carbs.
It would have been interesting to compare the results from two other companies whose tests I took: Orig3n and Helix. But both companies say they lost my test results. Neither sent replacement tests and both stopped answering emails and phone calls, even when I called and identified myself as a reporter. I have been unable to get a refund from either company.
Vitagene emails regular updates with advice on taking supplements — and offers to sell them to me. So, by the way, does Helix, even though it does not have my results.
Vitagene recommends I take 10-15 mg of zinc a day for “energy levels” and body weight. The U.S. recommended intake for zinc is 12 mg a day for an adult female, but people can easily get that from a balanced diet and zinc supplements are not recommended for anyone unless they have a deficiency. I do not.
Vitagene also recommends a variety of other supplements. One is made from the African bush mango, Irvingia gabonensis, to help control body weight, help control cholesterol and blood sugar. “Irvingia Gabonensis is high in fatty acids and fiber and has been shown to play a role in regulating the hormones related to appetite,” Vitagene claims.
But a team at the University of Exeter in Britain reviewed all the published studies on Irvingia gabonensis and found they were of such poor quality that there was no way to truly tell whether the supplements did anything at all.
The American Heart Association has published several studies showing there is not much evidence that vitamins can prevent heart disease or cancer. Even though half the U.S. population pops vitamins in the belief they can help people live longer, healthier lives, a very extensive look at the studies that have been done show it may be a waste of time when it comes to preventing the diseases most likely to kill you.
Vitagene also recommends probiotics, without specifying which or why, but says they will help with body weight and something they call hormone support.
Probiotics are big business, with very little evidence to back up the claims. The global market was worth $41 billion last year, according to Polaris Market Research. The idea is simple: eat or drink supplements to encourage the growth of “good” or “healthy” bacteria. The problem is, researchers don’t yet know which bacteria are the “good" ones to have, or how to encourage them to grow with food.
The one exception is using fecal transplants to treat a serious bowel infection called Clostridium difficile.
So are any of the tests helpful in managing health?
“There is a lot of stuff that can’t be determined through your genes,” admits Vitagene’s Longyne.
“They’re really just for fun,” advises Robin Smith of 23andMe.
I got no information that I could use to change my diet or exercise habits.
“In the meantime we have some pretty good ideas on how to do a healthy lifestyle that pretty much works for everybody,” NHGRI’s Brody said.
The advice is the same whether it’s for keeping a healthy weight, avoiding cancer, lowering the risk of heart disease, diabetes or Alzheimer’s: eat plenty of fruits and vegetables, don’t eat too much meat (if you eat meat at all), choose whole grains over processed flour, cut back on sugar and salt, and exercise every day or almost every day.
No DNA test needed.
Note: After this story published, Kate Blanchard, chief operating officer of Orig3n, contacted me to apologize and offer a refund, as did Chris Hoffman, head of Helix customer care.