Good diet + exercise = less insulin in the brain and a longer life!

Scientists in the U.S. say reducing the action of insulin in the brain could well be the secret to longevity.

They are advocating exercise as a means of keeping young because it reduces the action of insulin in the brain.

The researchers created mutant mice that over-ate, got fat and even had symptoms of diabetes, and yet lived 18 percent longer than normal lab mice and the secret was they lacked a certain key gene that affects insulin, the hormone that regulates glucose.

The researchers say the genetic engineering mimicked the effects of eating less and exercising and provides further proof of why exercise is good for the body.

It also offers a new explanation of why this is so.

Dr. Morris White, a Howard Hughes Medical Institute investigator at the Children's Hospital in Boston says the results also question how desirable it is to use insulin to treat type 2 diabetes.

Previous research in fruit flies and roundworms has suggested that reducing the activity of the hormone insulin, which regulates blood sugar levels, can increase lifespan.

As a rule people who exercise regularly live longer and some research has also suggested that putting animals on a strict diet also extends their life but this has not yet been shown to be so in people.

Dr. White and his team set out to see if the two effects were linked; they looked at insulin, because both fasting and exercise make cells more insulin-sensitive, meaning they respond more efficiently to the effects of insulin.

They also looked at the entire insulin pathway, a series of actions in the cell that control the body's use of insulin.

The team engineered mice that had no working copies of one of the genes involved in this pathway, called insulin receptor substrate 2, or Irs2.

Mice with no copies of Irs2 had defective brains and diabetes, whereas mice with one working copy lived 18 percent longer than normal mice.

They were also more active than normal mice, and after eating, their brains had higher levels of a compound called superoxide dismutase, an antioxidant that protects cells from damage.

White says diet, exercise and lower weight keep the peripheral tissues sensitive to insulin, which means the body needs to make less insulin.

The researchers said the engineered mice lived longer because the diseases that kill them, such as cancer and cardiovascular disease, were being postponed due to reduced insulin signaling in the brain, even though circulating levels of insulin were high.

They suggest that in the future, it may be possible to design drugs to reduce IRS2 activity to reproduce the same effect, although they would have to be specific to the brain.

The team is now planning research into possible links between IRS2 signaling and dementia, which research has shown is associated with obesity and high insulin levels.

The research is published in the journal Science.