Why Fat People Always Feel Hungry - I've been reading a lot about diets and obesity, and I've finally come to some conclusions which have been corroborated in Gary Taubes' paradigm-shattering book, Good Calories, Bad Calories.
The body regulates fat metabolism very precisely in ALL people--fat, lean, and in-between.
In a few sentences - Digestion of carbs and sugars leads to insulin secretion. Insulin secretion tells your body to store fat in fat cells. Insulin secretion also prevents your body from releasing fat from fat cells. You cannot lose weight (burn fat) with insulin in your bloodstream.
In other words - Insulin prevents your fat cells from releasing fat. So if you reduce your blood insulin levels (through low-carb eating), you enable your body to burn fat. But if you keep insulin levels high (through high-carb eating), you absolutely CANNOT burn fat.
The model 1 below explains why people get fat and why fat people constantly feel hungry.
In simple terms, when you eat, your body uses the fuel it needs, and any excess is stored as fat in fat cells. During the time between meals, your body signals the fat cells to release its stored fat. When your fat cells don't respond fast enough to your body's demand for fuel, the body tells your brain to make you feel hungry. Hunger drives you to eat, which increases the fuel immediately available, satisfying your body's demand.
The reason an obese person constantly feels hungry is because his fat cells are responding too slowly to his body's demand for fuel. When an obese person's body isn't getting enough fuel from fat cells, the body tells his brain to feel hungry. It cannot be helped.
Put another way, even though obese people have plenty of fat reserves, they feel hungry because their fat cells won't release fat fast enough to satisfy their body's fuel needs. That inevitably leads to hunger. They cannot help but feel hungry. Their body wants fuel, and if the fat cells can't deliver, the body will get the fuel it needs by making the person hungry.
Hunger is nothing more than a signal that your body needs fuel and that fat cells are not able to supply the fuel.
What causes the fat cells to release fat too slowly?
Insulin resistance - When you eat carbs, your body breaks the carbs down into glucose, which enters the bloodstream. The glucose in the blood triggers the pancreas to secrete insulin. Insulin tells your body's cells (including fat cells) to pull glucose from the bloodstream into the cell. When glucose is transfered into a cell, it is used for energy. A by-product of this energy creation is a glycerol molecule. Glycerol molecules have a special affinity for free lipid (fat) molecules. In fact, free floating lipids start binding to the glycerol to create triglycerides (each glycerol molecule binds three lipid molecules). Once lipids (fats) are bound into triglycerides, the fat cannot leave the cell. It's stuck in the cell. Effectively, the fat cell has just gotten fatter--all due to you eating carbs.
So it's carbs, which break down into glucose, that cause you to get fat, not the fats themselves. If you ate only fat and your body did not secrete insulin, you would not--could not--get fat. You couldn't get fat because in order for a fat cell to get fatter, it needs a glycerol molecule. Glycerol molecules are not made unless glucose is pulled into the cell. And glucose won't get pulled into the cell without insulin, which won't be secreted by the pancreas unless the blood contains glucose derived from the carbs you eat.
Evidence for this can be found in victims of type I diabetes. A person with type I diabetes is unable to get fat because his or her pancreas does not produce insulin. Without insulin, a diabetic person absolutely CANNOT store fat. Then only way a type I diabetic can store fat is by injecting insulin.
When insulin is in the bloodstream of a person (whether diabetic or not), the hormones that signal fat cells to release fat WILL NOT WORK. In fact, as long as insulin is in the bloodstream, fat cells WILL NOT RELEASE FAT. Without fuel from fat cells, the body signals your brain to make you hungry.
Since carbs drive insulin, and insulin makes you fat, if you remove the carbs from your diet, you absolutely will lose fat. Why? Because without the carbs, there is no insulin. Without the insulin, your body CANNOT store fat. But most important, without the insulin, fat-releasing hormones can finally do there job. Without insulin, you fat cells can release fat.
Obese people are often insulin resistant. That is, their cells do not respond very readily to insulin. As a result, blood glucose level remain high, signaling the pancreas to keep pumping out insulin. This keeps blood insulin levels chronically high in a insulin resistant person. And since blood insulin levels are high, NONE of the fat-releasing hormones that signal fat cells to release fat will work. In other words, an insulin resistant person CANNOT release fat from their fat cells because chronically high blood insulin levels prevent fat-releasing hormones from working.
To beat a dead horse, fat cells cannot release fat while insulin is in the bloodstream.
Fat cell size - The amount of fat released from a fat cell (in response to appropriate hormonal signals) seems to be directly related to the size of the fat cell.2 The more fat in the cell, the faster the rate of fat release. The smaller the fat cell, the slower the rate of fat release. This relationship creates something of a control or feedback mechanism which, along with other hormones, helps regulate a person's stable weight. As fat cells release fat, they become smaller. Because they are smaller, they release less fat. At some point, the rate is slow enough that the body isn't getting the energy it needs, so it sends a signal to make you hungry. That point of transition where the fat cells are too small to release fat at a rate to satisfy the body's fuel demands is a person's stable weight.
1 The model is a gross simplification but, like a crude map, it will get you where you want to go, and provide a handy model for what's going on and why you do, or do not, get fat.
2 As you gain weight, your fat cells don't increase in number, they increase in size.
 | Good Calories, Bad Calories by Gary Taubes |