Leptin and Insulin
While the Energizer Bunny runs on batteries, our bodies run on hormones. Hormones tell our bodies to burn fat and lose weight or to store fat and gain weight or to keep our weights the same. There are two key hormones that regulate food intake and energy balance in our bodies. These are Leptin (which come from fat cells) and Insulin (which comes from the pancreas). Understanding these two hormones gives us an insight into how the diet and lifestyle choices can help you achieve and maintain a healthy weight.
The hormone leptin is produced by our fat storage cells (called adipocytes). It acts as a negative feedback control for "fatness." What I mean about negative feedback control is that this hormone (and others like insulin) act the same way the thermostat controls temperature in our homes. When the temperature reaches the set temperature, the heat or air-conditioning turns off. In our bodies, fat cells release leptin in direct proportion to the amount of stored body fat. It enters our brains and stimulates a reduction in food intake and increases our energy use. In other words, leptin tells your brain that you have enough energy stored and to stop eating and get moving!
Your body can become leptin resistant too. This can happen from obesity , over-consumption of energy, fasting, consuming too few calories or losing weight. Leptin is a tricky hormone. Originally, it was thought that leptin told the brain to stop eating. Recent studies now show that leptin mediates the adaptation to fasting. That means that fasting or consuming too few calories on a regular basis causes lower leptin sensitivity (leptin resistance). This leads to increased hunger, food cravings and lack of energy. This has a very important implication - after you lose the weight you want (i.e. you have achieved weight maintenance), the reduced leptin sensitivity (leptin resistance) is likely responsible for lowered metabolism and increased hunger. This combination tends to lead to weight gain. This is why we often regain all of the weight after a diet! We've all heard of the "Yo-Yo" diets.
There may also be a link between leptin and cortisol (a steroid the body makes normally or when under stress). There appears to be a spike in cortisol levels in response to intermittent fasting. I talked more about cortisol in an earlier blog.
If I were to ask you the question "What does insulin do in our bodies?", most of you would respond that it lowers blood sugar. You are only partially correct. The hormone insulin is released by the pancreas in response to increased blood sugars. It does help move glucose into our cells, but it also signals our livers and muscles to convert glucose into glycogen (the best way to store carbohydrates in the body). We can store between 12 and 48 hours worth of glycogen for future energy use. When we have reached our max for glycogen storage, increased insulin levels stimulate the liver to convert glucose into triglycerides (a form of fat). Insulin tells the body where to put this converted glucose for long-term storage. You guessed it, it's stored in our fat cells (adipocytes). Fat storage is more efficient than carbohydrate storage as there is 9 calories/gram of fat compared to 4 calories /gram of carbohydrate. There is another very important function of insulin. It tells the brain whether or not to eat and also tells the brain about the energy status of our bodies.
When blood sugars are elevated for a long time, we can develop insulin-resistance. In other words, our bodies do not respond appropriately to increased blood sugars and ultimately, we can develop Type 2 Diabetes mellitus.
Leptin and Insulin - Implications in Weight Loss
There are two major points to remember about the hormones leptin and insulin:
- We need to control insulin levels by avoiding high blood sugar. This is important for regulating hunger.
- Slow and steady wins the race in terms of weight loss, leptin sensitivity and lessening the chances of weight rebound.