Individuals with a family history of diabetes type 2 who overeat for a specific period put on more weight than other people of the same age and lifestyle who overeat to the same extent. In other words, short-term overeating results in more weight gain for people with a genetic predisposition to diabetes type 2.

The 28-day study took place at Sydney's Garvan Institute for Medical Research, Australia. The researchers attempted to copy the type of overeating that generally occurs over the Christmas holidays.

The study involved 41 volunteers: 17 were healthy individuals who had a family history of Type 2 diabetes 24 were healthy individuals who did not have a family history of Type 2 diabetes Both groups were matched for age, weight and lifestyle Each volunteer had to overeat by 1,250 calories per day - 1,250 calories per day more than their energy requirements. The energy requirement of each individual was carefully calculated beforehand.

The volunteers were given a variety of high-fat snacks, such as crisps, chocolate bars and dairy desserts to consume, apart from their normal diets.

Each person's weight, fat distribution and blood insulin levels were measured: At the start of the trail Three days into the trial And on the 28th day of the trial The scientists found that: Those with a family history of diabetes Type 2 gained an average of 3.4 kilograms Those without a family history of diabetes Type 2 gained an average of 2.2 kilograms Those with a family history of diabetes Type 2 gained 1.2 kilograms more than the other group.

The family history of diabetes Type 2 group also had more insulin in their systems after just 3 days into the trial, before they showed any detectable difference in weight gain from the other group.

Dr Dorit Samocha-Bonet, Dr Leonie Heilbronn and Professor Lesley Campbell have published their findings in the international journal Diabetologia, now online.

Professor Campbell, senior researcher at Garvan and Director St Vincent's Diabetes Services, said "It's already well-known that relatives of people with Type 2 diabetes are more likely to develop it themselves. We wanted to challenge these individuals with overfeeding while they were still young and healthy, without any metabolic impairments."

"Our study shows just how quickly the body reacts to overeating, and how harmful it can be in susceptible people. While we expected differences between the two groups, we were surprised by the amount of extra weight the diabetes-prone group gained."

An early warning sign of diabetes is the development of 'insulin resistance', usually triggered by excess body fat. Insulin is a hormone made by the pancreas, which helps the body use glucose for energy. Insulin resistant muscle cannot respond properly to insulin from the bloodstream, leading to high levels of sugar in the blood. High blood sugar levels damage tissues and organs, so the body works very hard to reduce them by producing more insulin. Eventually, the insulin-producing cells in the pancreas become exhausted and Type 2 diabetes develops.

"Insulin resistance can start to develop at least a decade before clinical diabetes, and this study helps us examine its very early stages in healthy adults," said Dr Samocha-Bonet.

At the end of the study, participants were helped to lose weight, with both groups being equally successful. Interestingly, the 'biggest loser' belongs to the group with a family history of diabetes.