Sunday, February 1, 2009
If I'm so fat, why am I always hungry?
Body fat serves a number of purposes. It cushions our organs, it insulates us, and it provides a way to store energy. A normal amount of body fat is about 10-20% for men and 15-25% for women. So far, so good.
But sometimes we get too fat. What then? It seems logical to expect that our appetites would decrease, the extra fat would be burned as energy, and we would return to a normal fat percentage once again. But as millions of overweight people can testify, that is not how it always works. They can eat a meal, leave the table feeling full, and two hours later they will be ravenously hungry. They look down at their rolls of excess body fat and wonder, "Why in the world am I hungry? Why can't I just use some of this fat instead of having to eat again?"
In most cases, the answer is one word. Insulin.
Insulin is a hormone which is secreted by the pancreas whenever we eat carbohydrates or protein. Insulin sends a message to the tissues of the body--store nutrients! It is not practical for us to eat continuously. So we eat discrete meals, use some of that energy immediately, and (in response to the signal from insulin) store the rest for use later. Several hours after a meal is consumed, our insulin levels will normally fall, and this will permit nutrients to come back out of storage until it is time for our next meal.
As people get older, the insulin response system may begin to break down. The pancreas has to secrete more and more insulin in order to store nutrients following a meal. The elevated insulin takes longer and longer to return to normal levels, until it stays somewhat elevated all the time. As insulin levels stay high, it becomes progressively harder for stored nutrients to be released between meals. In other words, energy (mostly in the form of fat) is being stored at mealtime, but the energy in the fat can no longer be released efficiently between meals. The result? If a person has excess fat stores but also has persistently high insulin levels, he will be less and less able to access the energy he has stored, but will be forced to eat frequently to provide his body with the energy it needs. Even though he is fat, because of elevated insulin, he will find that he is always (or almost always) hungry.
Obviously the next question is, if a fat person wants to overcome constant hunger, how does he address his elevated insulin? This post, Reversing Insulin Resistance, shows that simply eating a low-carbohydrate diet significantly reduced insulin levels in a small group of obese type 2 diabetic patients. For a more detailed answer, please see this post. It summarizes the three primary strategies for lowering insulin (eat low-carb, eat moderate protein and wait 5-6 hours between meals) and gives several more suggestions for bringing insulin levels (and hunger signals) back into a normal range.