Drop in both insulin and leptin needed for fat burning to occur

Researchers have found that metabolism moves from using glucose to burning fat when there is a drop in both insulin and leptin levels.
The study has been led by Gerald I. Shulma, professor of medicine, cellular and molecular physiology, and physiological chemistry at Yale University. The research could point towards improved understanding of how best to lose weight which could benefit many people with diabetes.
Prior to the study, it was known that mammals can switch from burning carbohydrates, like glucose, for energy towards burning fat instead. This allows mammals to get energy without breaking down muscle mass.
It was thought that a decrease in insulin levels is all that was needed to help the switch to burning fat occur. However, the new research has identified that a reduction in leptin levels is also needed.
Insulin and leptin are both hormones. Insulin works to decrease blood sugar levels by moving glucose out of the blood and into neighbouring cells where it can be used directly as fuel or stored as body fat. A higher level of insulin also prevents fat from being broken down for energy. Leptin is a hormone which is linked to appetite and plays a key role in energy regulation.
In their study, the researchers from Yale investigated the rate of carbohydrate and fat metabolism as rats went from a fed to a fasted state. The researchers observed that as the rats fasted, leptin levels decreased and activated a pathway that led to fat burning rather than carbohydrate burning.
During fasting, the rats’ use of stored glucose went down and sugar levels decreased as a result. In turn, levels of insulin and leptin decreased. The rats’ bodies then broke down body fat to be turned into ketones for energy.
The team concluded that whilst insulin levels needed to drop for fat burning to start, a decrease in leptin levels was also required for this to happen.
The findings could help researchers to understand how different lifestyle changes affect the chances of success in weight loss.
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The study is published in the Cell journal.