Edward Weiss, Ph.D., assistant professor of nutrition and dietetics at Doisy College of Health Sciences at Saint Louis University, looked at a relatively common version of a gene called FABP2, which is involved in the absorption of fat from food.

Those people with the variant gene processed fat differently than those who don't have it. They burned more fat, which may have hindered their ability to remove sugar from the blood stream and burn it. Diabetes is characterized by too much sugar in the blood.

"This study adds to what was previously known about this gene variant by showing that after consuming a very rich milkshake, people with the variant gene process the fat from the drink differently than other people," Weiss says.

That is not to say that half of U.S. residents are destined to get diabetes, he adds.

"While the variation of the gene appears to contribute to the diabetes risk, it does not cause diabetes by itself," Weiss says.

"Many other genes, some known and some unknown, are involved in a person's overall risk of developing diabetes. Those are things a person can't control. But there are risk factors for diabetes that a person can change -- lifestyle factors, such as diet and exercise."