Low-calorie diets have long been known to thwart diabetes. Now scientists believe they know how and why.

Boston University researchers have discovered factors in the blood of rats places on calorie-restricted diets alter the function of insulin-producing cells in the body that regulate blood sugar levels.

The result: Low-cal diets have a positive impact on insulin levels and protect cells from fatty acid and blood-sugar toxicity, according to the study, published in the Federation of European Biochemical Societies’ FEBS Journal.

If the findings are confirmed in follow-up studies involving diabetics, they could lead to a new way to treat or even prevent Type 2 diabetes in those at risk for the metabolic disorder, the researchers say.

"Our findings support the concept that the impact of diet on insulin secreting cells is mediated by signals traveling through the blood rather than the nutrients and metabolites themselves,” said lead researcher Dr. Orian Shirihai. “These signals may be generated elsewhere in other organs such as fat tissue, liver, brain, or even the immune cells.

“Our findings also suggest that at least in part the beneficial effect of reducing caloric intake is mediated by the appearance of a protective signal rather than the elimination of a harmful one."