According to conventional wisdom, healthy eating means keeping your intake of saturated fats, salt, and sugar at a low level and eating enough vegetables, fruits and whole grains to increase your vitamin and mineral requirements. And of course not consuming more than a modest amount of caffeine, correct? Generally, the answer is “yes”.
Recently on the Genetic Literacy Project, for instance, we discussed the advantages of the Mediterranean diet, which reduces the risk of heart disease, strokes, diabetes and probably cancer, while slowing down aging. Together, these conditions account for the majority of deaths on the planet. And so, if you’re looking for a one-size fits all diet, this is the one to pick. You won’t know exactly how much it will reduce your risk for the most common causes of death, but it will reduce the risk to some extent, and for many people that’s reason enough to stock up on nuts and olive oil.
On the other hand, for many other people it’s just not enough. To change their diet, more importantly to stick to it, they really need to know it’s the right diet for their personal situation. That is the finding of a new study by University of Toronto researchers in nutrigenetics, an emerging field that combines genetics and nutritional science.
Diets are not all the same, but neither are people
For certain individuals, aspects of the Mediterranean diet may not be healthy. For instance, due to variations in several genes, sensitivity to dietary salt varies in the human population. One person may be perfectly healthy eating olives with his humus, while the another’s blood pressure may be elevated, because the olives bring her salt intake beyond what she can tolerate, given her genes. The same thing would be true if she eats salted nuts, and we can describe similar conundra in connection with tolerance to carbohydrates and diabetes susceptibility, or with tolerance to different types of fats and susceptibility to blood cholesterol conditions.
And so, even for a diet shown to be as broadly beneficial as the Mediterranean, an individual’s response to it depends strongly on his or her specific genetics. That should be no surprise, given our exponentiating awareness of the power of genes. What’s new from the Toronto study, however, is the finding that personalizing dietary recommendations based on a person’s genes actually helps people to adhere to the recommendations.
Rather than looking at how genetics affects the risk for a particular health condition, the researchers asked a question that was more about human behavior. Specifically, the trial was conducted “to determine the impact of disclosing DNA-based dietary advice on eating habits.” That’s according to University of Toronto Associate Professor Ahmed El-Sohemy, who holds the Canada Research Chair in Nutrigenomics.
Using information from healthy volunteers reporting their intake of four substances–sugar, sodium (salt), caffeine, and vitamin C–the research team divided subjects into two groups. One group received genetics-based nutrition advice on how much sugar, sodium, caffeine, and vitamin C to consume. In contrast, the other group received standard nutritional guidance based on up to date recommendations for the population, but not genetically personalized for the subjects.
After three months, and even more so after a year, subjects that were given genetically-based advice on how much salt to consume were found to adhere better to recommendations than subjects who received only standard, non-genetic based advice. In particular, subjects who were told to reduce their salt intake, because they carried a gene for salt sensitivity that could lead to high blood pressure, adhered to a low salt diet better than people who were given standard salt recommendations.
In terms of the other three dietary substances–caffeine, sugar, and vitamin C–the study did not find that genetic based recommendations helped with adherence to recommendations. However, according to the researchers, most of the volunteers were following recommended guidelines for those substances anyway when the study began.
So the real message here revolves around the salt finding. Would the same idea hold true for subjects requiring extra attention to their intake of sugar or saturated fat, also due to genetics? It seems logical that it should, but expanding that conclusion from salt to other food components will require additional studies.
David Warmflash is an astrobiologist, physician, and science writer. Follow @CosmicEvolution to read what he is saying on Twitter.