Tryptophan is why diets don't work.

Tryptophan helps you to feel “content” and satisfied”.
Like most Americans, I tried many diets and found that all of them were short-term band-aids on a major problem. As you know, the reason most diets don’t work is because it’s hard to stay on them.

Almost every popular diet deprives you of foods that contain the amino acid tryptophan. Tryptophan is the one main natural chemical that causes you to feel “content” and “satisfied.”

When you diet, you almost always lower your intake, and you soon feel like you’re deprived of something. In fact, you’re creating a mild case of depression. Without realizing it, you begin cheating on your diet until, once again, your body is getting the tryptophan it needs.

Deprive yourself of tryptophan and NO diet will work for long. Tryptophan is an essential amino acid that is necessary for the production of vitamin B3 (niacin). It is used by the brain to produce serotonin, a necessary neurotransmitter that transfers nerve impulses from one cell to another and is responsible for normal sleep. Consequently, tryptophan helps to combat hyperactivity in children, alleviates stress, is good for the heart, aids in weight control by reducing appetite, and enhances the release of growth hormone. It is good for migraine headaches and may reduce some of the effects of nicotine. Sufficient amounts of vitamin B6 (pyridoxine) and C, folate, and magnesium are necessary for the formation of tryptophan, which, in turn, is required for the formation of serotonin. A study reported in the Archives of General Psychiatry found that women with a history of bulimia nervosa, an eating disorder, experienced relapses after they took an amino acid mixture lacking tryptophan. Researchers believe that insufficient tryptophan altered brain serotonin levels and, consequently, the transmission of nerve impulses. A lack of tryptophan and magnesium may contribute to coronary artery spasms.

The best dietary sources of tryptophan include brown rice, cottage cheese, meat, peanuts, and soy protein. This amino acid is not available in supplement form in the United States. In November of 1989, the U.S. Centers for Disease Control (CDC) reported evidence linking L-tryptophan supplements to a blood disorder called eosinophiliamyalgia syndrome (EMS). Several hundred cases of this illness—which is characterized by an elevated white blood cell count and can also cause such symptoms as fatigue, muscular pain, respiratory ailments, edema, and rash—were reported. After the CDC established an association between the blood disorder and products containing L-tryptophan in New Mexico, the U.S. Food and Drug Administration (FDA) first warned consumers to stop taking L-tryptophan supplements, then recalled all products in which L-tryptophan was the sole or a major component. Subsequent research showed that it was contaminants in the supplements, not the tryptophan, that was probably responsible for the problem, but tryptophan supplements are still banned from the market in the United States. According to the FDA, at least thirty-eight deaths were attributable to the tryptophan supplements.