Honey, do these genes make me look hypertensive?

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This article was published 21/11/2017 (3159 days ago), so information in it may no longer be current.

We all know that we should eat better, exercise more, cut down on salt and sugar, increase our intake of fibre and whole grains.

But does it sometimes seem like a fool’s errand, trying to keep up with the latest health recommendations? When your annual checkup reveals normal blood pressure and cholesterol levels, it’s tempting to decide those “rules” are merely suggestions.

But what if you knew for a fact that your unique genetic markers meant consuming more omega-3 fatty acids could reduce your triglycerides? Would you make a meal of mackerel more often?

What if you were told the conventional wisdom about moderate caffeine consumption didn’t apply to you? Would you cut out coffee completely if you knew it would decrease your risk of a heart attack?

There are already many genetic-testing kits on the market that claim to unlock the mysteries of your personal genetic code, allowing you to make decisions that directly affect your health.

The research fuelling these tests comes from the field of nutrigenomics, the scientific study of the relationship between genes, nutrition and health.

Studies have shown, for example, that in some people, high blood pressure is positively related to salt intake; those people tend to have a variation of a certain gene. Therefore, if you know you have that variation, you might seriously consider reducing your sodium intake.

Nanci Guest is a registered dietitian and PhD candidate in the department of nutritional sciences at the University of Toronto. She is one of the researchers behind Nutrigenomix, one of the genetic tests currently on the market. She says the link between salt and blood pressure is a good example of how one size does not fit all when it comes to health recommendations.

“These government guidelines only apply to 70 per cent of the population that have the genetic risk (sodium-hypertension connection),” she says. “However, 30 per cent of the population will not see a lowering of their blood pressure with a reduction in their dietary sodium. Furthermore, some individuals actually need more salt, and a low-sodium diet may have adverse health outcomes for some.”

Via a saliva sample, Nutrigenomix tests 45 genetic markers, including HLA, thought to be predictor of gluten tolerance, and CYP1A2, which is related to how well you metabolize caffeine.

The tests are not available directly for consumer use; they are administered by a health-care provider or sports-fitness professional, including dietitians, doctors and coaches. (The Wellness Institute at Seven Oaks General Hospital is offering Nutrigenomix tests under the supervision of a registered dietitian for $500.)

“There are so many nuances in dietary recommendations that would be suited to an individual’s unique goals, food preferences, food intolerances and budget, for example, that it’s almost an impossible task to be automated…” Guest explains via email.

“The issue of compliance is also important and receiving guidance from a professional increases the odds that you will in fact follow his/her recommendations. Accountability at play here, as well.”

Peter Eck is an associate professor in the department of human nutritional sciences at the University of Manitoba. While he is an enthusiastic proponent of nutrigenomics and the idea of personalized medicine, he’s not as enthusiastic about the currently available tests.

He points out that 23andMe, an American company that was one of the first to sell personal genetic tests, was prevented from providing consumers with information about disease risk in the U.S. In the absence of controlled clinical trials validating the links between gene variations and outcomes, the FDA insisted that the company cease making health-related claims. (The FDA has since relaxed its stance and allows the company to give consumers information on gene mutations related to 10 diseases, including Parkinson’s and Alzheimer’s.)

Eck stresses that only about 10 genetic variations have been definitively linked to a health outcome. One of those is BRCA-1, which entered the public consciousness after actress Angelina Jolie had a double mastectomy and her ovaries removed when a DNA test revealed she had this gene variant, which substantially increases the risk of developing a type of breast and ovarian cancer in women with a family history of those cancers.

“All the stuff we know about genetic association — and that’s what you have to know about this genetic research, we only started in about 2006 or 2007 to develop the methodology to do associations — if you do associations, that’s an epidemiological term and it means something comes together: it is correlation; it is not a causality,” Eck explains.

“If you say, ‘This variation or this genotype is associated to a high risk of heart disease,’ which 23andMe did, and it comes from these kind of epidemiological studies, it is not really validated, it is not proven, but that’s what these companies operated with.

“Now all these other companies operate on that (premise) as well, but the consumer doesn’t know that.”

Here, Guest points out that Nutrigenomix is not used to predict the risk of developing a particular disease.

“All of our recommendations are actionable,” she says. “We are in the metabolic/modifier gene business, not predicting disease (telling you that you have an elevated risk for diabetes, yet providing no actionable advice). The genetic variants we work with change or modify actions like absorption, transport, response or metabolism of nutrients. This is basically our ‘individual nutritional biochemistry.’

“We are talking about the scientific evidence between nutrition and health.”

But Eck believes the science behind the personal genetic tests on the market needs to be spelled out more clearly to consumers.

“I went to conferences and I raised the issue with the owners of these companies and they said, ‘Oh, the consumer must know (that these are just associations).’ But how does the consumer know? As a scientist, I know what an association means, I know when 23andMe tells me, ‘Your risk for heart disease is 20 per cent higher with that genotype,’ it probably doesn’t mean much in real life.

“It needs to go to a clinical trial where we can say that these people under these conditions react differently based on their genotype, and there are not so many clinical trials.”

Researchers at the University of Manitoba’s Richardson Centre for Nutraceuticals are hoping to begin rectifying that situation. They’re looking for participants to take part in a study that will put one of these associations under the microscope.

Epidemiological studies have shown people whose cholesterol is lowered with the use of plant sterols tend to have a specific gene variant. The clinical trial, called GenePredict-PS, will work the concept backward to explore the hypothesis that people with that gene variant are actually more likely to respond favourably to sterols than those who don’t have the variant.

“Say you have variation A and variation B of a gene,” says Dylan MacKay, a nutritional biochemist at the U of M. “We’re going to select an equal number of people with A and an equal number of people with B and then we’re going to compare their response (to plant sterols). But we know that they’re A and B and the numbers, rather than just getting 20 people, giving them the sterols and looking at what their (genetic) variations are afterward.

“The strength is that we’ve designed it to test the test. We’re saying beforehand, based on our data, these people are going to be responders and these people are not going to be responders. And then when they do the trial, you’ve predicted it, so it’s a stronger test.”

The double-blind study spans three months. During the first 28 days, participants head to the Richardson Centre five mornings a week, where they are provided with breakfast that includes margarine that either contains plant sterols or is a placebo dose. They are provided with another container of margarine to consume at home for evening meals.

There’s a month off — “a washout period,” MacKay says — then participants return for a third month of breakfasts. Again, subjects and testers don’t know whether the margarine is a placebo dose or one that contains sterols.

It’s the type of study Eck would like to see more often. He says large epidemiological studies should be used to create hypotheses and point researchers toward areas of interest on the genome.

“And then you also set up clinical studies and really test it in very controlled environment where you don’t have confounders, because confounders in an epidemiological study are real bitches; there could be something completely different causing the effect.”

If the GenePredict-PS study does find a definite link between a specific genetic variant and plant-sterol efficacy, MacKay says the ease of adding sterols to someone’s diet might result in more positive behavioural change than a finding that asks them to give up something they love, such as salt or coffee.

MacKay, Eck and Guest all agree that knowing what’s best for us doesn’t always mean we make the right decisions. The hope is that more health information that’s tailored directly to us will strike a more personal chord.

“Behavioural change is our biggest hurdle, no matter what health improvements we seek,” Guest says, though she adds that most of her clients have sought her out and are motivated to change. “Strategies here are no different; however, we do have evidence that a ‘personalized’ approach to any desired change is superior than a dietary ‘call to action’ addressed to everyone.”

MacKay, however, remains skeptical about the real-world effects of fact-based advice.

“Behaviour change, especially around diet, is influenced by many other things — societal influence, environment, all these things you’d have to work on to modify your diet. It can be very difficult,” he says. “There’s individual variability there, too: how likely are you to make a change based on a recommendation? Are you more likely to make a change if there’s good scientific evidence that your genotype should be eating this way?

“There’s been some preliminary trials, but I haven’t been overwhelmed by the evidence yet.”

 

jill.wilson@freepress.mb.ca

Twitter: @dedaumier