The kitchen of the future, says one leading scientist, is likely to be equipped with dispensers to deliver your personalised prescription of nutritional supplements. A daily dose might be squirted into your morning coffee. Or perhaps, says Jeffrey Blumberg, professor of nutrition science and policy at Tufts University in Massachusetts: “A 3D printer will include the nutrients you need in a bespoke piece of chocolate in your favourite shape.”
Genetic science is already taking us closer to a healthcare model aimed at preventing disease based on individual propensities, rather than waiting to treat symptoms. John Hesketh, a molecular biologist at the University of Newcastle medical school, has referred to personalised nutrition as the holy grail of healthcare. “It would be preferable to tailor treatment to the individual, rather than to a group or just the population generally,” he says.
The NHS Genetics Education website (aimed at NHS staff) agrees: “In the future … we may be able to recommend a diet rich in foods that contain a particular nutrient that acts by ‘switching off’ a gene that contributes to the development of specific chronic diseases, such as high blood pressure, Alzheimer’s disease …”
Consumers are already being targeted by commercial online nutrigenetics services such as NutriFit and DNAFit. Send them a saliva swab, or a 23andme DNA test (now available in Superdrug), and they claim they can work from that. DNAFit says it looks at 45 gene variants to see if a person has lactose intolerance, sensitivity to alcohol, coffee, carbohydrate or saturated fat, an increased need for omega-3, B vitamins, antioxidants, vitamin D or cruciferous veg, and the risk of coeliac disease. Using this information, it provides food shopping lists.
The common gene variants involved are known as single nucleotide polymorphisms (SNPs). According to Keith Grimaldi, chief scientific officer of DNAFit: “For an SNP to be included in our nutrigenetic screen, it has to have been studied in specific gene-diet interaction studies, and the results have to be repeated several times.”
A few SNPs are well-established to dictate certain outcomes, such as those associated with increased need for folic acid and vitamins B6 and B12, and caffeine sensitivity. But Grimaldi admits that advice, such as: “Reduce saturated fats, eat more cruciferous vegetables, and so on” is less precise. “The result is a probability for an individual and becomes less black and white.”
So is the advice these commercial companies provide worthwhile? Hesketh is not convinced that we yet know enough to effectively tailor diets based on gene testing. “The data that is coming out is complex,” he says. “In many cases, we are still trying to identify the main genetic variants that might affect cancer risk, heart disease risk, and whether genetic variants in combination with particular diets might affect that risk.”
Web-based consumer nutrigenetics companies are limited to offering a lifestyle service rather than medical advice, which is stringently regulated. Their bespoke diets are really just subtly tweaked versions of standard nutritional guidelines. The trouble is, says Hesketh, that although the SNPs that DNAFit, for example, looks at might be sensible: “They’re unlikely to be the only ones. So it may give you some information, but not the whole picture. It may be helpful, but it may not. It depends if people think it’s worth the investment.”
José Ordovás, director of nutrition and genomics at Tufts University, who has worked in the field for 30 years, says: “The scientific knowledge is still fragmented and incomplete. There are so many factors.”
Take gut bacteria, for instance. Nutrigenetics can tell you if you don’t produce lactase, the enzyme needed to digest lactose, but that doesn’t necessarily mean you are lactose-intolerant. “Some people who don’t produce lactase can consume milk because their gut bacteria will ferment lactose,” says Kevin Whelan, professor of dietetics at King’s College, London.
Ordovás is sceptical of commercial genetics advice on omega-3, and fat and carbohydrate sensitivity. He says he has just read a “very nice paper, showing omega-3 is beneficial only for those – at least from a neurological perspective – who have the E4 genotype. We have to be always updating, correcting. It’s a moving target. And regarding fat and carbs, they are using papers we’ve published. They are not doing their own research and are not familiar with all the tricks of the trade.”
The one current benefit of direct-to-consumer nutrigenetics, he says, could be motivational. “If you have that more passionate approach of thinking: ‘This is what comes out of my genes’, you might stick to a healthier diet.”
However, Whelan, who has carried out a systematic review of studies on the motivational powers of nutrigenetics advice, says: “It hasn’t really been shown to increase motivation and actual weight loss. When you look at the population, some lose weight, some don’t, and some put on weight, so overall there’s no effect.”
This isn’t to say that nutrigenetics is a damp squib. “We have gained a lot of ground,” says Ordovás. “For decades there has been a fight over the benefits of the Mediterranean diet versus the low-fat diet.” A five-year study of 7,000 people has shown that those carrying two copies of the genetic mutation for diabetes, and who were on a low-fat diet, were almost three times as likely to have a stroke as those with one or no copy of the mutation. Conversely, mutation carriers who increased their consumption of nuts and olive oil (key components of the Mediterranean diet) neutralised their risk.
“As long as you don’t overreach on your promises,” says Ordovás, “even with the knowledge we have now, you can start sending people in the right direction, in terms of what will be better for them.”
