Can your genetic makeup help you lose weight? Some companies are offering genetic tests that they claim can tell you what you need to eat, and what not to eat, to be healthy.

But do they work?

Phyllis York gave it a try. A year ago, her health was deteriorating and she was considered morbidly obese. Her weight was keeping her from doing the things she loved so she decided it was time to improve her health.

"I had the full package of DNA testing done by Genelex," said York.

In that package was a genetic nutritional test that looks at variations in 19 genes. After sending in a swap of her cheek, York was sent back her nutritional genetic profile.

"This nutrition package is just for me ... I've learned, for instance, I need more B vitamins than the average person," said York. "I also watch the caffeine."

The test costs $400. Some 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 with the University of North Carolina.

A spokeswoman from Genelex said the genetic nutritional test gives people realistic steps to take to improve and maintain a healthy lifestyle.

"They know what they need to focus on. They know what's most important for their own unique body," said Christine Ashcraft, with Genelex Corp.

"It's understandable, it's very clear and the advice is very pointed," said York.

It's the specific suggestions of foods and daily supplements that has helped York.

"I've changed my diet," said York.

She's replaced snacks with nuts, white flour with barley and wheat flour and red meat with fish.

"I've lost about 40 pounds," said York. "And healthwise, I feel great."

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 say it will take another five to 10 years of research to know how to do it.

To learn more about getting a nutritional genetic profile, call (800) 523-3080.