By Paul Nicolaus
November 13, 2017 | We've all heard the same dietary advice. Cut back on fatty foods. Take it easy on the sugar. Eat more fruits and veggies. But these recommendations tend to be based on a decades-old "one size fits all" model and generalizations made about the population at large. In the meantime, a growing body of research has suggested that the same foods and beverages can affect different people in very different ways.
Health Canada's guidelines suggest a daily intake of no more than 400 mg of caffeine per day for most healthy adults, for example, which is the amount found in about three to four cups of brewed coffee. But research shows that this recommendation is only good for about half the population.
For the other half, explained Ahmed El-Sohemy, professor in the Department of Nutritional Sciences at the University of Toronto, drinking more than two cups a day increases the risk of hypertension, pre-diabetes, and heart attack because of a variation in a gene that makes this group less efficient at breaking down caffeine.
There are other genes that determine how much consumed vitamin C ends up in our circulation and whether sodium increases our risk of salt-sensitive hypertension. These genes essentially alter what is considered "healthy" and help explain why some are turning to the promise of personalized nutrition in the hopes of maximizing diet-related health benefits.
But can nutritional recommendations based on genetics be used to optimize our health or even fend off disease at this stage of the game? "That is the holy grail of this whole field," said Hooman Allayee, professor of preventive medicine and biochemistry & molecular medicine at the University of Southern California. While many are pushing that agenda, turning all the hype and hope into reality will be a tall order.
"Figuring out the genetic variation part in people is not a problem at all," he said. "Figuring out the diet is where it gets really messy." The real difficulty is quantitating the diet of large numbers of humans to identify valid gene-dietary interactions. It is not practical to send somebody to thousands of people's homes and watch what they eat all day long, he explained, so there is a reliance on self-reported questionnaire data.
If someone says they had a steak with a potato and some broccoli for dinner and then two eggs in the morning, that information is used to estimate aspects like the amount of protein or saturated fat intake. But it's easy to see how this method is fraught with inaccuracy, he said, and identifying interactions based on imprecise data offers up imprecise interactions.
Commercial Offerings
In the meantime, though, plenty of startups have entered the mainstream with tests claiming to help consumers make DNA-based dietary decisions. "People just gobble it up," said Allayee, noting that while it may sound sexy it doesn't necessarily work because it's all based upon gene-dietary interactions that are somewhat dubious. "I don't really see a whole lot of benefit."
When Martin Kohlmeier, research professor in the department of nutrition at the University of North Carolina, Chapel Hill and the UNC Nutrigenetics Laboratory considers the landscape of commercial offerings, he, too, sees plenty of cause for skepticism.
"There are many, many players who make a quick buck by making claims that are not supported by the evidence," he said. This presents problems for the average consumer who doesn't know any better. "For the layperson, most of the time it's not transparent. How would they know?"
But he also said there is a small number of reputable companies operating in this realm, pointing to Habit, an Oakland, Calif. company, as one recent case in point. Founded in late 2016, the personalized nutrition company sends users an at-home test kit that includes finger-prick blood tests and a “metabolic challenge” drink.
After gathering the first blood sample, users drink the shake and collect two more samples at timed intervals before sending it to a lab that looks at metabolic rate and searches for genetic variations in DNA. Customers also provide body metrics such as height, weight, and waist circumference as well as lifestyle habits such as exercise frequency.
This combination of information is used to help determine how users respond to food and create an individualized eating plan. Those in the San Francisco Bay Area also have the option of ordering meals and having them delivered right to their door.
Kohlmeier also highlighted Nutrigenomix, a company founded by the University of Toronto’s El-Sohemy, as another example of a sound business. Its health & wellness test examines genes that affect nutrient metabolism, body weight, cardiometabolic health, food intolerances, eating habits, and physical activity. (Kohlmeier disclosed no financial interest or other ties to either Habit or Nutrigenomix.)
Unlike virtually all other genetic testing companies in this space, however, the test kit is not made available directly to consumers. "Ours is the first genetic test kit developed exclusively for use by healthcare professionals, to enable them to provide personalized, DNA-based dietary advice to patients as part of their practice," El-Sohemy explained.
The test can indicate relative risk based on genetics and diet, including the risk of lactose or gluten intolerance. It can also help identify which nutrients a person needs to consume more or less of in order to minimize their risk of chronic diseases such as obesity, type 2 diabetes, and heart disease.
There are limitations, however. The test is not a diagnostic and is not intended to be used for the treatment or management of any disease, according to El-Sohemy, and it cannot be used to determine the absolute risk of developing a disease.
While the test currently includes 45 genetic variants, Nutrigenomix expects to continue to add new markers and encompass a larger set of genes and health conditions as the entire field grows and moves forward.
More Evidence Needed
The challenge of genetic testing has been resolved, according to Kohlmeier. This can now be done reliably and relatively quickly at a cost that continues to become more affordable over time. Even just a few years ago, he pointed out, that was a big deal. Now it’s old hat, and it’s become a commodity.
The challenge now is determining what information can be put to practical use in order to help professionals and consumers make sense of the many gene-food interactions and arrive at sound nutritional choices. "Evidence is the commodity that we need," he said.
While short-term effects, like the impact of caffeine, are much easier to verify because the experiments take less time, demonstrating long-term effects and exploring conditions like cancer or cardiovascular risk presents a much greater challenge. "The longer term the effects are," he said, "the harder they are to prove."
When he peers into the future of what will be possible, Kohlmeier said personalized nutrition will be similar to precision medicine in many ways. If it is known how someone is going to respond, medication or other interventions can be used much more effectively and the same goes for nutrition.
At this stage, the science is being built out. But that doesn't mean the field can't or shouldn't apply what is already known, he said. Think about the state of antibiotics back in the 1950s for a comparison. Most modern antibiotics were not yet around at that point, but that didn't mean the ones available at that time shouldn't have been put to good use.
Similarly, nutrigenetics is currently useful for specific instances and there are going to be many more coming aboard. “We don't need to say, ‘It's not ready—let's wait 10 years,’” he said, “because we can use those where we know they work.” Today, for example, it is possible to reliably predict lactose intolerance based on genetic information. "That's not future. That's current. And it's a very practical situation."
What one expert sees as an example of a practical application, however, another sees as a scenario that doesn't necessarily call for genetic testing. "Just call me every day and I'll say, ‘drink a glass of milk' and if after a week of doing this you say, ‘I can't do this anymore because of the discomfort' you're probably lactose intolerant," Allayee said. "No need for a test."
As he looks ahead, Allayee thinks the field could learn a thing or two from the pharmaceutical industry. Before bringing a drug to market, companies undergo rigorous clinical trials, then the FDA has to approve the data, and then a drug comes to market and is used to treat a certain condition. Some of that type of rigor needs to be applied to this new wave of DNA-based nutrition to help legitimize the field.
"I'm still optimistic," he said, "but I think that there's a scientific and rational way of approaching it." Once gene-dietary interactions are validated, then it could be presumed that individuals tweaking their eating habits will experience the expected benefits. And then it will be "ready for primetime."
"I know everybody wants this to happen, but the steps and the work that needs to be done to get there is not necessarily happening," Allayee said. And without that kind of data, it is his opinion that it just isn't possible to recommend dietary changes based on genetic information. "It's going to go that way, I think, but it's just going to take time."
Paul Nicolaus is a freelance writer specializing in health and medicine. Learn more at www.nicolauswriting.com.