The number of home DNA test kits that provide personalised nutrition and diet recommendations based on your genes is increasing. They’re based on the idea that, because each of us reacts to food differently, in part due to our unique genetic make-up, we all have different nutritional requirements. However, science is advancing, and there are calls for the industry to be more regulated. Is it possible to optimize your health by tailoring your diet to your genes?
The concept has existed since nearly two decades ago, when scientists completed the mapping of the human genome. However, DNA tests have become more affordable, faster, and accessible for use at home in recent years. Occasionally, they are referred to as direct-to-consumer genomic tests. Numerous tests are available, including kits for tracing your ancestry and determining your risk of developing certain health problems.
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Many companies, including Nutri-genetix, DNAfit, and 23andme, offer nutrigenomics tests for nutrition and diet. You order the kit online, send back a saliva sample or cheek swab, and your DNA is screened to determine if you have genetic variants associated with specific food reactions. While the tests vary, they frequently assess your risk of developing lactose intolerance and coeliac disease, as well as sensitivities to substances such as coffee, alcohol, carbohydrates, fat, and salt. The report you receive may include recommendations for foods to eat or avoid, strategies for losing or managing weight, and your vitamin and nutrient requirements.
How does it work?
Your DNA is screened for small variations in a small number of specific genes associated with specific food responses. These links come from population studies that looked into whether people who react to certain foods share gene variations. So nutrigenomic tests assess your susceptibility to certain foods. For example, your genetic profile may make you metabolise carbohydrates faster than average. To manage blood sugar spikes, you can theoretically alter your diet.
A test finding that you may react to nutrients in a certain way does not mean you will. In the words of Dr. Keith Grimaldi, Chief Science Officer of DNAfit: “Certain variants will affect the likelihood of a certain outcome.”
DNAfit, like most DNA testing companies, looks for gene variations that have “a reasonable level of scientific consensus, based on human studies.” Dr. Grimaldi says that if you have the genetic variant CYP1A2 (AA), you will almost certainly metabolise caffeine faster and thus feel its effects more strongly. People with MCM6 gene variations may also tolerate lactose, a sugar found in milk.
DNA tests aid in the prevention and management of obesity.
According to Vimal Karani, Professor of Nutrigenetics and Nutrigenomics at the University of Reading, DNA testing is being used to treat people with a genetic predisposition to obesity.
Obesity is strongly associated with variations in the FTO gene, also known as the ‘fat gene’. A high-carbohydrate diet and inactivity put people at ‘particularly high risk’ of obesity, according to research.
That doesn’t mean you’re doomed, Dr Karani emphasises, A healthy high-fibre diet and increased physical activity, he found, can reduce this genetic risk.
As of now, less than 5% of the genetic variants linked to obesity have been identified, according to Dr. Karani. Moreover, your genes are only one component of your body’s response to food.
“DNA tests are just part of the equation”, he says.
“An array of other biological markers need to be analysed too, including gut microbiome, metabolites (chemicals involved in bodily functions), blood sugars and fats, cholesterol, blood pressure and lifestyle factors”, to complete the picture.
Do DNA self-administered tests work?
However, according to Dr José Ordovás, Director of Nutrition and Genomics at Tufts University in Boston, we currently have a limited understanding of the interaction between genes, nutrients, and health. There are millions of genetic variants in human DNA, and scientists are still unsure how the vast majority of them affect how the body functions or how one variant affects another.
“For many of the traits DNA kits are testing for – sensitivity to fats and coffee, Omega-3 requirements and the like – there are scores of genes involved”, argues Dr Ordovás.
“The genes they’re testing for are just the tip of the iceberg.”
Researchers at King’s College London, Massachusetts General Hospital, and nutritional science company ZOE discovered that even identical twins can process identical foods differently, implying that factors other than genetics play a role in at least some conditions.
“Environmental factors have a profound influence”, says Dr Ordovás – “the time we eat, our stress levels, what we did the previous day, the season of the year, and of course, our microbiota [the organisms in our gut known to impact health]”.
But nutrigenomic tests might motivate some people to improve their diet, according to Dr Ordovás.
“If you follow the recommendations of one of these diets it may benefit you… but that’s not necessarily because it’s exclusively tailored for you. It may be because you change your eating habits for [the] better.”
Future of DNA tests
Dr Virani believes that nutrigenomic testing will become more meaningful when combined with other data about your unique digestive and metabolic processes: biological markers (such as blood sugar and fat), metabolites (metabolism-related molecules), and gut microbiome (the gut bacteria).
As of yet, no single test combines all of this information. ZOE, a health science company based in the United Kingdom, is about to launch an at-home test kit that analyses your gut, blood fat, and blood sugar responses to food. Additionally, some DNA testing companies offer blood tests in addition to genetic tests. However, much work remains to be done to help us understand the complex factors that influence our individual responses to food and how to combine this data into algorithms that generate useful tailored dietary advice.
Dr Virani envisages the day when precision nutrition, including nutrigenomic tests, will play a key role in improving the nation’s health.
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“If solid evidence is available that these precision nutrition approaches can reduce the prevalence of obesity and other chronic diseases, the government and the NHS should make these tests available free of charge to everyone”, he says. But he considers this “a long way off”.