When it comes to guiding how we should eat, nutrition advice generally takes a one size fits all approach. Although there may be differences depending on age and gender – or if a woman is pregnant or planning to be – the assumption is we all need similar amounts of vitamins and minerals to stay healthy.
But it’s also true that our genes sometimes influence how our bodies interact with certain nutrients and a new area of research suggests that tweaking our diet to meet those needs more precisely will do a better job of reducing the risk of disease.
This is no fringe fad but a branch of science called nutrigenetics that uses genetic testing to check for gene variants that affect how we respond to certain nutrients or foods.
Coffee is one example. Some of us have a gene variant that makes us metabolise coffee more slowly, which can increase heart disease risk. Other gene variants include one that confers an increased risk of type 2 diabetes in people who eat too many high GI carbohydrates, while another makes people more salt sensitive, causing a higher risk of blood pressure if they overdo the salt.
Other diet-related genetic quirks are ones that make it harder to get enough of the B vitamin folate; another causes people to metabolise saturated fat more slowly so they are more likely to gain weight if they eat too much of it.
A single saliva test developed by a University of Toronto biotechnology company, Nutrigenomix, can detect these and other gene variants and is available in Australia through some accredited practising dietitians. One Sydney dietitian, Kate Gudorf, sometimes recommends the test to clients with a family history of type 2 diabetes or heart disease.
“I find that using the test makes people more committed to improving their diet because they’re being given advice that’s tailored to them rather than a blanket recommendation,” she says.
But there are some misconceptions, says Julie Dundon, an Adelaide dietitian who also uses the test in her practice.
“Some people who are found to have the risk for type 2 diabetes if they eat too many high GI carbohydrates think that improving their diet means they won’t get type 2 diabetes. But although the test gives a clearer picture of their risk and what they can do to reduce it, we have to emphasise that this doesn’t guarantee preventing the disease.”
The test isn’t cheap – it costs about $285 plus the cost of a consultation with a dietitian. However it only has to be done once, Dundon says.
“I also think a key message is that there’s an interaction between genes and diet that can increase the risk of health problems for some people if they eat a certain way – if you eat too much saturated fat, too many high GI carbohydrates or too much salt, for instance. But if you don’t eat this way then you have a lower risk of these problems even if you do have the gene variants,” she says.
Another approach to preventing disease at a genetic level is a nutrigenomic test, the Genome Health Analysis, developed by the CSIRO to measure the degree of damage to DNA caused by poor nutrition and ageing, says Professor Michael Fenech, the researcher who led the team that created this test.
“We know that too much DNA damage can increase the risk of cancer and other degenerative diseases such as Alzheimer’s and Parkinson’s disease and reduce the capacity of tissues to regenerate – but we also know that diet and appropriate supplementation can help prevent or repair DNA damage,” he says.
The test costs about $500 and is available only at Reach 100, an Adelaide clinic specialising in preventive medicine.
One nutrient known to help defend and repair DNA is folate, a B vitamin found in foods like legumes, nuts, grains, green leafy vegetables and bread. Although wholegrain bread naturally contains some folate, white bread loses much of this in processing. But in one of those little ironies of food manufacturing, all Australian bread, except organic, is now made with flour fortified with folic acid, a synthetic form of folate.
While it makes sense to get plenty of folate from food, some people may have difficulty absorbing or metabolising it because of their genetic make-up or because they are low in vitamin B12 which works with folate to prevent DNA damage, Fenech says.
But taking high-dose folic acid supplements alone in the hope of protecting DNA may not be a good idea for everyone. He says there are concerns that excess folate may help some cancers to thrive and emerging research has linked too much folate in combination with too little B12 to cognitive decline in older people.