Skinny folk with an infuriating ability to eat anything they want may not be as fortunate as they seem.
For some, the excess calories that appear to vanish like magic could be increasing the risk of Type 2 diabetes.
Scientists have identified a number of gene variants that both increase diabetes susceptibility and prevent the growth of fat under the skin - especially below the waist.
The discovery could explain why some slim people develop Type 2 diabetes even though the disease is strongly associated with being overweight or obese.
Despite appearances, these individuals do not burn up extra calories from fattening food. Nor do they store the calories "safely" as peripheral fat. Instead, they transfer them to organs such as the liver and pancreas where they can do harm, it is claimed.
Lead researcher Dr Luca Lotta, from Cambridge University, said: "Our study provides compelling evidence that a genetically-determined inability to store fat under the skin in the lower half of the body is linked to a higher risk of conditions such as diabetes and heart disease.
"Regardless of their body weight, if people don't burn these excessive calories, even if they don't seem to be putting on a lot of weight, they may still be at risk.
"This doesn't mean that being obese is a good thing. It does mean that if you eat too much and you don't do enough physical activity you have an excess of calories you have to store somewhere.
"Not all individuals are predisposed to safely store those calories in peripheral fat tissue."
The international team studied more than two million genetic variants in almost 200,000 people to look for links to insulin resistance. The condition, marked by a decreasing ability of the body to respond to the hormone insulin, can pave the way to full-blown diabetes.
Co-author Professor Sir Stephen O'Rahilly, also from Cambridge University, said: "We've long suspected that problems with fat storage might lead to its accumulation in other organs such as the liver, pancreas and muscles, where it causes insulin resistance and eventually diabetes, but the evidence for this has mostly come from rare forms of human lipodystrophy.
"Our study suggests that these processes also take place in the general population."