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, using 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, increasing 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.

However, 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.

"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. 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."

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 researcher Professor Michael Fenech.

"We know that too much DNA damage can increase the risk of cancer and other degenerative diseases such as Alzheimer's and Parkinson's," he says. SMH