Body weight is usually discussed in connection with type 2 diabetes. New research suggests it may also matter in a very different way for some people already developing type 1 diabetes.
In an observational study of 833 people with early signs of type 1 diabetes, those who moved from overweight or obesity into a normal BMI range were less likely to progress to clinical disease over about four years. The association was strongest in children and teenagers and was not clearly seen in adults.
The finding, which was published in Diabetes Care, does not mean weight loss can prevent type 1 diabetes. The participants already had islet autoantibodies, signs that the immune system had begun attacking the insulin-producing cells involved in type 1 diabetes. Researchers also did not assign anyone to lose weight or follow a particular diet.
Instead, they asked a narrower question: Among people already at increased risk, was moving into a healthier weight range linked to a slower path toward clinical type 1 diabetes?
About 27% of participants reached a normal BMI range during follow-up. After researchers accounted for differences in age, starting BMI and how far type 1 diabetes had already progressed, those participants had about a 48% lower risk of reaching stage 3, the point at which type 1 diabetes becomes clinically diagnosed.
The difference was easier to see in absolute numbers. After four years, about 14% of participants whose BMI moved into the normal range had progressed to stage 3 type 1 diabetes, compared with about 21% of those who remained in the overweight or obesity range.
The association was most evident in young people.
Among participants younger than 18, moving into the normal BMI range was associated with about half the risk of progressing to clinical type 1 diabetes. Researchers did not find a clear association among adults.
For children, reaching a normal BMI range does not necessarily mean losing weight. A child may continue growing taller while weight gain slows or stabilizes, gradually moving into a different BMI category. That distinction is important because the study was not testing weight-loss programs for children.
The researchers also looked at different stages of type 1 diabetes development.
The association was not clear during the earliest transition, when a person moves from having one islet autoantibody to having multiple autoantibodies. But once the autoimmune process was more established, moving into a normal BMI range was linked to a lower risk of progressing from stage 1 to stage 2 and from stage 2 to clinical type 1 diabetes.
That pattern suggests body weight may have more influence on how quickly the disease advances than on whether the autoimmune process begins in the first place.
Still, there is an important reason to be cautious.
People whose BMI eventually normalized were already different from those whose BMI remained elevated. They tended to be younger and started with a lower BMI. They also had better measures of insulin sensitivity and a somewhat different metabolic profile.
That means researchers cannot tell whether reaching a different BMI range itself reduced the risk of progression or whether people who were already metabolically healthier were both more likely to normalize their BMI and less likely to progress quickly.
The study also could not determine why BMI changed. Researchers did not have consistent information on whether participants changed their diets, became more physically active, used weight-management medications or experienced normal growth-related changes.
Those limitations are especially important because type 1 diabetes is an autoimmune disease. Excess weight does not explain why the immune system begins attacking insulin-producing cells.
Researchers are instead investigating whether carrying excess weight after that process has started could place additional demands on the body's remaining insulin-producing cells. In exploratory analyses, measures related to insulin sensitivity appeared to explain part of the association, but the study was not designed to prove how weight might influence disease progression.
The results now provide a reason to test the idea more directly.
A future clinical trial could examine whether helping young people at high risk of type 1 diabetes follow a healthy growth and weight trajectory actually delays progression. Until that happens, this study cannot tell families that intentionally changing a child's weight will prevent or postpone the disease.
What it does suggest is that type 1 diabetes progression may be influenced by more than the autoimmune process alone, and that metabolic health could become one piece of a much more complicated picture.
The study was supported by Breakthrough T1D, formerly JDRF. Genetic data were supported by the National Institute of Diabetes and Digestive and Kidney Diseases. The TrialNet network receives support from the National Institutes of Health, including the National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Allergy and Infectious Diseases and Eunice Kennedy Shriver National Institute of Child Health and Human Development, as well as Breakthrough T1D.