While the dominating opinion is that rising insulin is a result of obesity and insulin resistance, a new study provides evidence that it appears to be the other way around.
According to the study, researchers found that when we eat too much, obesity may actually develop as a result of chronically high insulin levels. To prove this, the team used mice to show that animals with persistently lower insulin stay trim even as they indulge themselves on a high-fat, all-you-can-eat buffet. These results provide evidence that it is circulating insulin that drives obesity in mammals.
Study author James Johnson of the University of British Columbia added that the results are also consistent with clinical studies showing that long-term insulin use by people with diabetes tends to come with weight gain.
One of insulin's functions is management of the utilization of fat as an energy source. And because insulin controls the central metabolic processes, failure of insulin production can lead to diabetes type 1 or diabetes type 2.
In this study, Johnson and his colleagues used mice because they have two insulin genes: insulin1, which shows up primarily in the pancreas, and insulin2, in the brain and the pancreas. By eliminating insulin2 altogether and varying the number of good copies of insulin1, the team produced mice that varied only in their fasting blood insulin levels.
When the mice were presented with high-fat food, those with one copy and lower fasting insulin were completely protected from obesity, even without any loss of appetite. They also had lower levels of inflammation and less fat in their livers. These differences "reprogrammed" the animals' fat tissue to burn more energy.
Johnson stated that, "The high levels of insulin that are often found in obese individuals are not simply a side effect of weight gain, but rather they probably play a contributing role." "This is a major paradigm shift for most scientists in the field." Johnson also noted that it is important to recognize that insulin is neither "good" nor "bad."
"We always want the simple answer, but there are few of these in biology," he said. "Too little insulin results in diabetes, which is very bad and in no way would I want people with diabetes to not take adequate insulin. However, many people probably have more circulating insulin than we need."
According to Johnson, it isn't clear what these findings will mean for the future treatment of obesity and drugs designed to block insulin come with various unwanted side effects.
But for now, the best way to keep insulin levels low is to follow a healthy diet. Johnson recommends that people have two or three meals each day, and try to avoid snacks in between. He also recommends avoiding eating late at night or early in the morning.
"Personally, I believe that a diet with small portion sizes, enjoyed at a modest pace, and filled with whole, unprocessed foods is the healthiest," he said. "People should avoid the extremes of diets containing only one type of food."
Cell Metabolism, Dec. 2012