Puffs of insulin administered through the nose reduced food consumption by 11.7% in non-diabetic men compared with a placebo, but the insulin had no effect on their feelings of hunger, according to a study in the journal Diabetes. Previous research suggests insulin is among several hormones used by the brain to adjust and control energy levels and body weight in humans.
The study compared energy metabolism in the brain and food intake in experiments involving 15 German men in their mid-20s. In one, subjects received four puffs of intranasal insulin before breakfast and, in the other, they received a placebo substance, also through the nose. Following both experiments, subjects were instructed to eat as much breakfast as they wanted. Before and after eating, subjects underwent a type of imaging that measures cellular or metabolic activity in the brain.
Levels of adenosine triphosphate, an indicator of cerebral energy, were significantly elevated in subjects within 10 minutes of receiving insulin compared with the placebo, results showed. Intranasal insulin also raised phosphocreatine levels, another brain-energy indicator, but glucose and insulin levels in the rest of the body and feelings of hunger didn't change throughout the study. Intake of carbohydrates and protein were lowered the most, results showed. Intranasal insulin may be useful in treating obesity, researchers said.
The study sample,15 German men in their mid-20s, was too small to generalize the population. Also this study didn't include women or different age groups. They need to conduct both men and women and more diverse age groups for more generalized, solid result. In this study, they had a control group which was received a placebo substance through the nose instead of real insulin. This control group made the causal relationship more clearly, helping the researchers can be sure that the variable is causing the changes not by something else.