Leptin and insulin are protein hormones that circulate in your blood. Leptin is produced in your fat cells and insulin is produced in your pancreas. Leptin and insulin work together to control your appetite, the way that your body uses food for energy, your blood sugar levels and the amount of fat that your body produces and stores in fatty tissues. Obesity may interfere with the normal functioning of leptin and insulin.
Brain and Appetite
One of the main functions of leptin is to curb your appetite. Leptin is produced in fat cells, so when your fat cells grow in size, more leptin is produced. Leptin interacts with leptin receptors in a region of your brain called the hypothalamus. Leptin signals your brain that you have enough fatty tissue and that you are full and should stop eating. If you do not have much body fat, your blood leptin level will be low, the appetite center in your brain will not be inhibited and you will feel like eating.
A mutual interaction between leptin and insulin balances the amount of fat that you store and the amount that you use for energy. When you take in too many calories, insulin signals your tissues to produce and store fat. Insulin also signals your fat cells to produce more leptin. In turn, leptin signals your brain to stop eating and leptin signals back to your pancreas to stop producing insulin. Leptin also stimulates tissues, such as your liver and muscles, to burn some of the fat for energy.
Regular binges of overeating, especially fatty foods and refined carbohydrate foods, will force your pancreas to produce more insulin to stimulate both the transport of extra glucose from your blood into your tissues and the processing of extra fat for storage. Consequently, your pancreas may become resistant to the signal from leptin to stop producing insulin. Too much fat in fatty tissues and in other tissues where fat does not belong may cause your tissues to become nonresponsive or resistant to signals from both leptin and insulin. Thus, if you are considerably overweight, normal control over appetite and fat metabolism can be lost. Leptin resistance and insulin resistance can lead to type 2 diabetes and cardiovascular disease.
Leptin and insulin, through control of your appetite, fat production, fat storage and the use of fat for energy, work together to assure that you have enough body fat to maintain reproductive functions. However, too much fat in your tissues tends to impair the normal functions of leptin and insulin. Eat well to maintain enough fat in your fatty tissues, but don’t overeat, especially fatty, refined carbohydrate and sugar-sweetened foods. Extra calories often get deposited as fat in tissues where it does not belong. Choose a diet that is low in saturated fats, refined flours and sugars and rich in whole-grain foods, vegetables and fruits.
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Michael Peluso is a semi-retired scientist in the field of nutritional biochemistry. He received his M.S. in nutrition from the University of California, Davis and Ph.D. in nutrition from the University of Missouri. Peluso's work has appeared in scholarly publications such as the "Journal of Nutrition," "Lipids" and "Experimental Biology and Medicine."