Genetically lowering plasma insulin levels by 25% extended median lifespan by 11% in female mice fed a low-calorie/high-carb/low-fat diet and by 3% in female mice fed a high-calorie/high-fat/low-carb diet.
This study looked at the effects of genetically lowering insulin levels in older mice. Unfortunately, the male mice did not have lower plasma levels of insulin despite genetically lowering insulin-genes and so the effect on lifespan could not be determined in male mice.
The female mice were fed two diets: (diet A: moderate-energy diet of 4.68 kcal/g, with 20% of calories from protein, 25% from fat, and 55% from carbohydrate; diet B: high-energy diet of 5.56 kcal/g, with 16% of calories from protein, 58% from fat, and 26% from carbohydrate).
Interestingly, the lowering of circulating insulin through gene manipulation had a more profound effect on median lifespan in female mice fed the low-calorie/high-carb/low-fat diet (11% extension) versus the high-calorie/low-carb/high-fat diet (3% extension). It is important to note that diets A and B were not matched for the type of fat content, protein levels, or micronutrient composition, so there are numerous potential factors that could have impacted diet-dependent outcomes.