For years, Andrew Bederman says he has been looking for ways to live a longer, healthier life. He decided to turn somewhere new: his own DNA.
At least six companies now market genetic tests that they claim can identify people at increased risk of disease, while offering advice about how to change their diets to reduce the risk.
Bederman decided to try out one of these.
"The pamphlet suggests it will tell you about your cardiovascular health [and] your bone health," he told ABC News. "And it will tell how you process and metabolize things that you eat."
Using a mail-order kit, Bederman collected his genetic sample by wiping a swab on the inside of his cheek. He shipped the swab to Genelex Corp., a DNA testing lab in Seattle. A computer will look for variations or changes on 19 specific genes in the sample, company officials said.
"These 19 genes are the most important genes currently known with scientific background that are actionable -- meaning that if you have these variations, you can make changes to your current dietary or lifestyle habits," said Kristine Ashcraft of Genelex Corp.
For example, a variation found in a gene called MTR has been associated with heart disease, so the lab suggests getting more B vitamins to reduce the risk.
A variation found in the VDR gene has been linked with weak bones, so people with this characteristic are urged to get extra calcium and vitamin D, either from specific foods or daily supplements.
"They take the test," said Ashcraft. "They know what they need to focus on. They know what's most important for their own unique body."
The test can cost $400, and most nutritionists say it's a waste of money.
"We just don't know enough to use those types of tests effectively," said Dr. Steven Zeisel, associate dean for research in the School of Public Health at the University of North Carolina at Chapel Hill.
Critics say the test may put the mind at ease, but it does nothing for one's health. They add that analyzing just 19 out of the more than 20,000 genes is not nearly enough to identify people at increased risk.
"It's very naive to focus on a few select genes for any given disease," said Jim Fleet, associate professor of foods and nutrition at Purdue University in West Lafayette, Ind. "We know there are many contributors, genetic contributors, to every complex disease."
It is not known how much more of a given vitamin a person with a particular gene variation may have to take or whether the extra vitamins would help at all.
The idea of using a person's unique genetic makeup to create an optimal diet is something many nutritionists say has great promise. But they estimate it will take at least another five to 10 years of research to know how to use it.
"In the future, this could be really just the way we do nutrition medicine," said Zeisel.
In the meantime, most researchers say people should forgo the tests and do what they've been told all along: choose their foods sensibly.
ABC News' John McKenzie filed this report for "World News Tonight."