Leptin is a protein that is produced in fat cells and the levels rise and fall according to how much fat is stored in these cells. The more fat, the higher the level of leptin. It travels to the brain to signal whether or not there is enough stored energy in your fat cells to engage in normal metabolic processes. Once your leptin levels reach a certain threshold, and this threshold is different for everyone, it signals to the brain that you can exercise, burn energy and eat at a normal rate. In other words, it controls metabolism, hunger and feelings of satiety – when leptin levels are sufficiently high, the brain signals that there is no need to eat as much because you have enough stored energy. Your metabolism also increases when leptin levels rise over a certain threshold.
If there is not enough fat in your fat cells to produce sufficient leptin, the brain receives a signal that says there is not enough stored energy and that you need to eat. With these lower levels of leptin, your metabolism will slow down to help conserve energy.
So, when a person is carrying excess fat the levels of leptin rise, signalling the brain to send a message to eat less and increasing metabolism. Why then do people keep gaining weight? Surely the higher levels of leptin would mean that their appetite is curbed and their metabolism sped up.
The problem arises when there is so much leptin in the blood stream (from too much fat in the fat cells) that the cells of the brain become “resistant” to the leptin and don’t receive the signal to reduce eating. This leptin resistance is similar in principle to insulin resistance, when the cells of the body become resistant to insulin because there is too much floating around in the blood stream.
Because the brain is not receiving these leptin signals, it thinks the body is in starvation mode and sends a message to increase appetite and decrease metabolism.
Interestingly, this is why people who are trying to lose weight often hit a plateau, where the weight loss stops. Because there is a decrease in the amount of fat in the fat cells, there is also a decrease in the level of leptin reaching the brain – so the brain thinks the body is in starvation mode and sends the message to decrease metabolism and increase appetite. If this happens while trying to lose weight, the best thing to do is to have a day of eating a little bit more, the body then produces more leptin which signals for an increase in metabolism.
The problem of incorrect leptin levels and leptin resistance is a complex one and there are various factors that can contribute to it including:
- Insulin resistance. Insulin and leptin work together to control your metabolism. Insulin triggers the production of more leptin, so if insulin levels are high, so too are leptin levels, potentially leading to leptin resistance.
- High triglyceride levels – Triglycerides are a bi product of the metabolism of fructose, sugar and grains. These triglycerides block the passage of leptin to the brain, tricking the brain into thinking the body is in starvation mode.
- Excess fructose consumption. Athough eating 2 pieces of fruit per day is healthy, be careful not to overindulge. High levels of fructose, usually consumed through fruit juices and foods sweetened with high fructose corn syrup, can wreak havoc on your leptin levels. Firstly, it inhibits the leptin receptors in the brain which as mentioned previously tricks the brain into thinking the body is in a starvation mode and signals an increase in appetite and a decrease in metabolism. The second way fructose affects leptin levels is through the production of triglycerides, as mentioned above.
- Excess consumption of simple carbohydrates (sugar, refined and processed foods like white flour). Like fructose, sugar and refined carbohydrates (grains) produce triglycerides as a bi product of their metabolism, resulting in either leptin not getting to the brain or the leptin receptors in the brain becoming resistant.
- High stress levels – Many studies have shown that continued high levels of stress raises leptin levels in the blood. Cortisol is released during times of stress, and too much cortisol causes the body to store more fat, which in turn produces more leptin. Stress can also contribute to insulin resistance, another contributor to high leptin levels. Cortisol also decreases the level of hormone called adiponectin, which is responsible for suppressing appetite and speeding up metabolism, amongst other roles.
- Lack of sleep – Studies have shown that a lack of adequate sleep decreases the amount of leptin produced, which once again means that the brain is not getting sufficient signals to increase metabolism and decrease appetite.
Leptin is also involved in many other bodily processes. It plays an important role in bone, heart and immune health and plays a role in the pathogenesis of hypertension.
Leptin’s role in women’s fertility is an important one. If there is either insufficient leptin reaching the brain or leptin resistance, the brain signals the endocrine system to alter its production of female hormones. If you can imagine back to caveman era, this was the way the body ensured that women did not fall pregnant during times of famine, when there was insufficient food to nurture a pregnant woman.
So, if you have some or all of the following issues, you may have leptin resistance:
- Overweight and find it difficult to lose the weight
- Hungry a lot of the time
- Metabolism is slow
- Fertility problems
- High blood pressure
- Poor bone health
- High triglyceride levels
To reverse leptin resistance, the following steps need to be taken:
- Reduce (preferably eliminate) consumption of sugar, fructose, refined carbohydrates and processed foods which will help lower triglycerides and help reverse insulin resistance
- Eat a diet filled with whole foods, fresh fruit and vegetables, lean meat, nuts and seeds
- Avoid calorie restricted diets, or “crash” diets
- Reduce stress levels
- Get plenty of quality sleep
- Exercise regularly
Despite the fact that there has been much research on leptin since its discovery in 1994, we still have a lot to learn about this important hormone. It is not necessarily the only answer to why people become and remain overweight, but it is at least another part of the puzzle.
By Andrea Southern, Naturopath, Clinical Nutritionist, Herbalist.
References:
http://www.marksdailyapple.com/leptin/#axzz1zftxJ9il
http://www.webmd.com/diet/features/the-facts-on-leptin-faq?page=2
http://www.naturalnews.com/040864_leptin_resistance_diabetes_stress_management.html