Could a DNA diet test transform your health?
by Sue Quinn The number of home DNA test kits offering nutrition and diet advice matched to your genes is growing. They’re based on the idea that each of us responds to foods differently, in part due to our unique genetic make-up, so we have individual nutritional needs. But the science is emerging and there are calls for greater regulation of the industry. Could tailoring your diet to your genes help you optimise your health? The concept has been around since scientists finished mapping the human genome almost 20 years ago. But recently DNA tests have become cheaper, quicker and more available to use at home. They are sometimes known as direct-to-consumer genomic tests. Different kinds of tests can be bought, including kits for exploring your ancestry and assessing your risk of developing certain health conditions. Nutrigenomics tests are designed for nutrition and diet, and are offered by many companies, including Nutri-genetix, DNAfit and 23andme. You order your kit online, post back a saliva sample or cheek swab, and your DNA is screened to find out whether you carry genetic variations linked to certain food responses. The tests vary, but often they assess your risk for conditions such as lactose intolerance and coeliac disease, and sensitivities to things like coffee, alcohol, carbohydrates, fat and salt. The report you receive back might include advice about foods to eat or avoid, how to lose weight or manage your weight, and your requirement for certain vitamins and nutrients. How do the tests work? In nutrigenomics tests, your DNA sample is screened for small variations in a limited number of specific genes associated with particular food responses. These associations are based on the findings of population studies into whether people who react in a certain way to particular foods have gene variations in common. As such, nutrigenomic tests assess your predisposition to certain food responses. For example, depending on your genetic profile you may metabolise carbohydrates more quickly than average. In theory, you can then adjust your diet to manage spikes in your blood sugar. But if a test finds you’re likely to react to nutrients in a certain way, it doesn’t mean you definitely will. “Genetic predispositions are exactly that”, says Dr Keith Grimaldi, Chief Science Officer of DNAfit. “Certain variants will affect the likelihood of a certain outcome.” Like most DNA testing companies, DNAfit screens for gene variations where there is “a reasonable level of scientific consensus, based on human studies” they will have a particular effect. Dr Grimaldi says if you carry the genetic variation CYP1A2 (AA), for example, you will “almost certainly” metabolise caffeine faster than someone who doesn’t, and therefore feel its effects more strongly. It’s also likely people with variations of the MCM6 gene will tolerate lactose, the sugar found in milk. DNA tests are sometimes used to check for lactose tolerance. DNA tests help reduce and manage obesity DNA testing is being used successfully in research projects to treat people with a genetic predisposition for obesity, according to Vimal Karani, Professor in Nutrigenetics and Nutrigenomics at the University of Reading. Variations in the FTO gene, also known as the ‘fat gene’, are strongly associated with a higher risk of obesity, particularly among certain ethnic groups. Research shows those who carry at least one copy of specific FTO variations, and who eat a high-carbohydrate diet or are physically inactive, are at ‘particularly high risk’ of obesity. Carrying these variations does not seal your fate though, Dr Karani stresses. His research in low-income countries suggests adopting a healthy high-fibre diet and increasing physical activity could reduce this genetic risk. “There are several genetic testing centres in these countries successfully prescribing personalised diets for people to prevent and reduce obesity”, he says. With less than five percent of the genetic variations responsible for obesity identified so far, research in the area is still in its infancy, says Dr Karani. What’s more, your genes are only part of the complex system involved in 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. Obesity genes have been identified, and some DNA tests check for these. Do DNA home test kits work? But we currently have limited knowledge about the interplay between genes, nutrients and health, according to Dr José Ordovás, Director of Nutrition and Genomics at Tufts University in Boston. There are millions of genetic variations in human DNA, and scientists still don’t know how the vast majority of them influence the way the body functions, or how one gene variation 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.” Studies carried out by researchers from King’s College London, Massachusetts General Hospital and nutritional science company ZOE, show even identical twins can process the same foods differently, which suggests factors in addition to genetics are important for 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.” Environmental factors, such as sleep, stress and gut bacteria, in addition to genes, have been found to influence our responses to food. DNA tests of the future Dr Virani believes nutrigenomic testing will become more meaningful when combined with other data about your individual digestive and metabolic processes: biological markers (such as blood sugar and fat), metabolites (the molecules involved in your metabolism) and gut microbiome (the gut bacteria). Health science company ZOE have launched an at-home test kit in the UK that analyses your gut, blood fat and blood-sugar responses to food. And some DNA test companies offer blood tests as an add-on to their genetic tests. But there is still much work to be done to help us understand the complex factors that affect our unique responses to food, and how to combine all the information 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. “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”. In June 2021, a Parliamentary Committee published its first report into direct-to-consumer genomic testing. It urged the Government to require manufacturers to have the performance of DNA tests “assessed by an external body” before putting them on sale in the UK, to ensure they’re reliable and deliver the promised results. The government responded in November 2021 explaining they would be investigating further Originally published June 2021