March 7, 2014
Hunger Hormones Do More Than Just Make You Hungry
Hunger can be stimulated by the filling and emptying of your stomach. Your stomach has stretch receptors to detect if there is food in there or not. When your stomach is empty you fell hungry. When it is full, you feel full. This mechanical filling and un-filling is not the only way to detect hunger / satiety. You have hormones that communicate with your brain whether or not you are hungry. The two hormones I want to focus on are ghrelin and leptin.
Ghrelin is a hormone that is released by your stomach when it is empty. When your stomach is low on fuel, ghrelin is released and travels to the brain. There, it tells your brain, "hey, you are running low on fuel... time to look for food." You then feel that hungry urge and begin to search for food. This is a pretty simple representation of ghrelin; it is a hunger hormone. You also have a satiety hormone called leptin. Leptin is released from your fat cells and is a long term food regulator. You also have short term satiety regulators that are released from your gut, but that is for another day. Because leptin is released from your fat cells, the more fat you have, the more leptin you should have. Leptin travels to your brain and says, "hey... you are full. You are not hungry and do not need anything to eat." These two hormones have another key role as well: metabolism modulation. Ghrelin will decrease your resting metabolic rate and leptin will increase it. This makes sense if you think about it. If you are hungry, you could be starving, and your body would want to conserve calories, so ghrelin tells the brain you are hungry, and tells the body to slow down its metabolism. Leptin, on the other hand, increases metabolism. This, too, makes sense. If you eat a lot of food and store some of it as fat mass, your body will try to maintain its set-point by increasing metabolism in order to maintain your weight.
In a healthy body, these hormones work together to keep an individual at a healthy weight and also send normal hunger and satiety signals. However, when you start messing with the system, things can go awry. If you feel that a starvation diet is the best way to go, then your ghrelin levels will be chronically high and will result in a depressed metabolism. If your stomach is not full, your metabolism could suffer. This is just one of the reasons why we recommend getting in adequate amounts of fiber and protein. They are low in calories and can suppress ghrelin release. But leptin is a real kicker...
Let's say, for example, that you LOVE your sugar. Well, you eat your sugar and this causes your body to release insulin. Insulin is an anabolic hormone so it tells your body to increase energy storage. It actually travels to the brain and inhibits leptin's ability to signal the brain it is full. In a normal system where you eat some food, your insulin goes up, and then falls back down due to digestion, this is normal. If you eat a lot of excess sugar, this can chronically clog your system so that your brain thinks you should always be in an anabolic state. Lots of sugar = lots of insulin = less leptin doing its job = decreased metabolism. This is also true if you are insulin resistant, have metabolic syndrome, or type 2 diabetes. In these conditions, insulin levels are always high. It is always telling the body to stay anabolic and not to increase metabolism.
Another thing that will throw this system haywire is poor sleep. Research has shown that poor sleep actually increases ghrelin levels and decreases leptin levels. This not only means that you will be hungrier and have stronger cravings, but that your metabolism could decrease as much as 400 calories per day. That is a BIG drop. Also, given that your cravings for sugar will be stronger, you are more likely to eat worse and trigger a greater insulin release. This, too, will keep you from burning the calories you want.
The body is an amazing and complex system. Treat it well and it will treat you well in return. Hopefully, understanding how these hormones function will make you think twice about sacrificing your sleep or skipping your next meal.
Keep at it!