High Insulin Levels Could Result in Obesity
Study sheds new light on the link between high insulin levels and weight gain.
-- by Alexia Severson
While the dominating opinion is that rising insulin is a result of obesity and insulin resistance, a new study published in the Cell Press publication Cell Metabolism 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.
The results are also consistent with clinical studies showing that long-term insulin use by people with diabetes tends to come with weight gain, said study author James Johnson of the University of British Columbia.
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.
The Expert Take
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.
“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,” said Johnson in an interview with Healthline. “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.”
Source and Method
Animal protocols were approved by the University of British Columbia Animal Care Committee in accordance with national and international guidelines. Groups of male mice were randomly divided into two diet groups at weaning (3 weeks), and fed a control diet (25% fat) or a high-fat diet (58% fat). Body weight, fasting glucose, glucose tolerance, and insulin tolerance were examined after 4-hour fasts according to standard methods.
After 52 weeks of age, mice were scanned for whole-body fat to lean mass ratio via NMR Spectroscopy at the 7T MRI Research Center at the University of British Columbia. Circulating fatty acids were measured with the Wako NEFA kit.
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.”
A study published in 2003 in The Journal of Clinical Investigation studied the link between chronic inflammation and insulin resistance, revealing that “many inflammation and macrophage-specific genes are dramatically up-regulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity.” However, researchers concluded that more research was needed and that it remains to be shown how WAT ultimately causes systemic insulin resistance.
In another study published in Cell Metabolism in 2005, researchers found that insulin, along with generating fat, helps keep fat in the liver under control. According to the researchers, these findings suggest that fasting between meals is important in maintaining a lean and healthy liver by allowing insulin levels to rise and fall.
Researchers in a study published in 2004 in JAMA found that the hormone dehydroepiandrosterone (DHEA) significantly reduced abdominal fat and improved insulin action in elderly people. They concluded that DHEA may be able to reduce abdominal fat, as well as the risk for diabetes that often occurs as we grow older.