Last updated on June 7th, 2017
Can spitting into a test-tube tell you which diet is best for you?
Earlier this year, Anita and I each sent in a sample of our saliva to 23 and Me, a company that does commercial genetic testing. I’m not plugging the service, and this is not intended to be a full-scale review. But some of our DNA test results are relevant to the topic of diet.
We both opted to receive ancestry and health-related reports of our DNA. At first, I was only going to get the ancestry report, but changed my mind after getting that report and seeing Anita’s full set of reports. (Note: Anita has agreed that I may share her results in this post.)
Ancestry Results
My ancestry report showed that my DNA background is nearly 95% northern-western European. There was a smidge of Iberian way back, and a little southern European, too. The tests revealed more than 1200 genetic relatives of mine in the 23 and Me database, including two first cousins I’ve never met. We share a grandfather whom I also never met because of a bitter divorce. I’d been told that this grandfather was part Native American, but if so, none of those genes showed up in me. That’s entirely possible if the last 100% Native American ancestor of mine lived six or more generations ago. There are limits to what your DNA can tell you about your ancestors.
Anita’s ancestry is, as she expected, heavily Italian with some French-German mixed in.
Health and Wellness Results
The other sets of reports covered genetic health risks, carrier status, inherited traits, and wellness. Regarding genetic health risks such as Late-Onset Alzheimer’s and Parkinson’s, neither of us had the genetic markers that 23 and Me tests for. We also were not found to be carriers of 42 genetic variants for conditions that we don’t have but could pass on.
The so-called “Wellness” report examines how a person’s DNA influences his or her body’s response to environmental factors. This category is more interesting for our purposes. There are eight environmental responses tested for, of which four have a direct connection to diet and/or weight. Here are those four, and the DNA test results for Anita and me.
| Anita | Jim | |
| Lactose intolerance | Likely intolerant | Likely tolerant |
| Saturated fat & weight | Weight likely to be greater on a high saturated fat diet than a low saturated fat diet | Weight likely to be similar on high or low saturated fat diets |
| Caffeine consumption | Likely to consume more | Likely to consume more |
| Genetic weight | Predisposed to weigh about average | Predisposed to weigh about average |
The interesting thing about our supposed DNA influenced responses to lactose is that neither Anita nor I are lactose intolerant, even though her DNA predicts that she is likely to be. Being able to consume lactose in the form of cream and cheese is convenient for everyone, but especially so for anyone eating high fat and low carb.
Our DNA says that we both are likely to consume more caffeine than the average person. According to the 23 and Me website, we are predicted to drink about a quarter of a cup of coffee more per day than average. That’s a very conservative prediction. Our mutual coffee habit isn’t what keeps us together, but it doesn’t hurt. Certainly, being able to drink coffee with heavy cream is a plus on an LCHF diet.
Neither of us can blame our genes for weighing more than the average person of our height, age and ancestry.
Saturated fat and weight
This leaves only one DNA-influenced environmental response to discuss, but it’s the most central and controversial where an LCHF diet is concerned: saturated fat and weight.
According to 23 and Me, based on my DNA, my weight “is likely to be similar on diets high or low in saturated fat with the same number of total calories.” The dividing line between “high” and “low” amounts of saturated fats is a measly 22 grams a day.
In fact, this prediction is inaccurate. At roughly the same calorie-levels, I have lost weight on a diet with higher amounts of saturated fat (and fats in general), and not lost weight on diets with lower amounts of saturated fat.
Of course, the X-factor being left out of the equation is carbohydrate consumption. I didn’t merely add saturated fat to my diet. I drastically cut carbs, too.
That said, it is true that I have had an easier time losing weight on an LCHF diet than Anita has. This is as our DNA results predict, at least if saturated fat consumption is the only relevant variable. But is it? For instance, I could be, and most likely am, deeper into the metabolic syndrome than she is. So my body may have been more primed for a positive response to reducing carb-intake, and thereby reducing blood glucose and insulin production.
Does my DNA have anything to say about eating carbs? Apparently not that these tests can tell. But I have a strong family medical history of type-2 diabetes, which suggests a genetic component to how my body reacts to excess dietary carbs. Anita does not have the same history.
Should we base our diets on such DNA test results? I don’t think so. To be fair, 23 and Me doesn’t say we should, either. When making the argument to restrict dietary saturated fat, 23 and Me cites not DNA science, but the conventional wisdom of the Dietary Guidelines for Americans.
No thanks. As Huck Finn says, “I been there before.”
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