PERSONAL DNA PROFILES can reveal how much salt or coffee your body can handle, which foods your body might need more or less of for better health, and what kind of diet and/or exercise might work the best for losing weight. Using what’s called nutrigenetics – combining genetics and nutritional science – you can also assess personal gene-based food preferences and sensitivities to defend against those friendly food-police who keep pointing out what you should and should not eat.
In early 2015, President Obama announced the creation of a $130 million national database for some one million Americans, with genetic profiles, medical history and other data, from which algorithms could eventually create personalized meal plans. Meanwhile, genetic analysis along with lengthy diet and exercise recommendations can be yours with a mere cheek swab — but the price tag can be high, and skeptics contend that common sense is still the best approach to healthy diet and effective weight loss.
Gluten is the obvious example of gene-based food sensitivity: for people with a gene variant that makes them susceptible to celiac disease, eating gluten can lead to expression of that gene, setting off inflammation throughout the body and a host of health problems. (Besides the 1% of Americans who have genetically based celiac disease, an additional 6% believe they have “non-celiac gluten sensitivity.”)
In addition, processed meat can influence the expression of a genetic variant linked to increased risk of developing colon cancer. Reviewing records of some 20,000 people in four countries – the U.S., Canada, Australia and Germany — about half of whom had colon cancer, researchers at the World Health Organization looked at both genetic differences and at how much processed meat they ate. For the 47% of individuals with one genetic variant, eating more processed meat was associated with greater risk of colon cancer – although the odds may be different in different populations.
Genetic profiling also helps explain why nutrition studies often produce conflicting results. Coffee, for example, is metabolized quickly by about half the population — for whom the four cup limit is set; but for “slow-metabolizers,” drinking more than two cups a day can increase the risk of heart attack.
And, while the Mediterranean diet is generally the healthiest, its levels of salt – in olives, salted nuts, etc. — might be too high for those with the genetic variant that increases sensitivity to salt, according to the Genetic Literacy Project. For these individuals, consuming the same amount of salt is more likely to raise blood pressure to levels considered unhealthy and linked to heart disease.
Conversely, diet recommendations are better adhered to when based on genetic profiles, according to researchers at the University of Toronto. Healthy volunteers divided into two groups received recommendations on salt, caffeine, sugar and vitamin C consumption; but only one group received individual genetic profiles related to these ingredients. That group did better following the salt recommendations, but results weren’t clear for the other foods, because most volunteers were already following healthy guidelines for these.
Italian researchers conducting genome-association studies on more than 4,000 people from Italy and other countries found 17 independent genes that appeared to influence tastes for foods including coffee, artichokes, bacon, broccoli, chicory, dark chocolate, blue cheese, ice cream, liver, orange juice, plain yogurt, white wine, mushrooms and oil or butter on bread. And “none of these genes belonged to genetic categories associated with receptors for the senses of taste or smell,” according to University of Trieste researcher Nicola Piratsu.
In addition to these 17 gene variants, 19 more have been linked to metabolism. In one Italian study of 191 obese study participants, the group of 87 put on a diet customized to their genetic variants for metabolism and taste – accommodating, for example, for liking the taste of fats — lost 33% more weight than those in the control group at the end of two years. Piratsu confessed to being skeptical at first that there would be any difference: “It’s like having two cars which start at the same point and they move in directions which differ for only a degree. At first they will look as though they are parallel, but after 10 km they will actually be far apart.” Piratsu added: “One of the main contributions [to the customized diets’ success] will be in making the diets more pleasurable and thus more acceptable.”
With the understanding that some people are more likely to lower their weight on a low-fat diet, while others do better on low carbs, experts are beginning to rally to the idea of “eating to your genotype.” In a study of 101 obese and overweight women at Stanford University placed on one of four diets, those on a diet matched to their genetic makeup lost 5.3% of their body weight, twice as much as the control group who lost only 2.3%. In addition, those individuals following the lowest-carbohydrate Atkins diet and those following the lowest-fat Ornish diet based on their genetic profiles lost 6.8% of their body weight, compared to 1.4% for those following these diets not matched to their genotype.
Among an array of companies offering genetic profiles, the UK-based DNAFit examines 45 gene variants that reflect the body’s capacity to respond to nutrition and exercise. And Nutrigenomix will create diet and exercise recommendations based on analysis of seven genes that indicate sensitivity to vitamin C, folate, glycemic index, omega-3 fat, saturated fat, salt and caffeine.
The Nordiska system, developed by Newcastle-based myGenomics, provides diet and exercise advice based on eight genetic variants; in trials of more than 7,000 people, the average weight loss was 11 pounds over four months. A British writer for Men’s Health who tried the system (whose name, oddly, is not on the article) was disappointed to find that Nordiska matched you to only one of four nutritional types: “GI smart”— a diet designed to avoid spiking blood sugar; “Carb smart” — a diet limiting carbs to 40% of food; “fat smart” — a low-fat diet; and “balanced” — prescribed a diet that combines the other three. The writer was also disappointed to be placed in group four, which, he said, led to a “predictable combination” diet. Although, with the Nordiska recommendations for diet and exercise, he lost about 12 pounds in one month.
The roles of inheritance and experience on food-related genes, however, can be complicated. Individuals called “supertasters” inherit more taste buds and receptor cells than others, leading them to use more salt than others to block bitter tastes and to avoid strong flavors, especially sugary deserts. And one gene variant influences how much an individual can detect bitter tastes, causing some people to have a strong dislike of broccoli and other cruciferous vegetables. Finally, the more salt we use on our food, the more we crave it.
“What these tests really measure are what people are currently eating,” according to Catherine Collins of the British Dietetic Association, who is skeptical about the usefulness of expensive genetic profiling. “If you are eating a lot of fat, it will lead to the over-expression of certain genes…but you don’t need these tests to tell you that.”
— Mary Carpenter