As far back as 1975, researchers demonstrated that administering 5-HTP) to rats that were bred to overeat and be obese resulted in significant reduction in food intake. It turns out that these rats have decreased activity of the enzyme that converts tryptophan to 5-HTP and subsequently to serotonin. In other words, these rats are fat as a result of a genetically determined low level of activity of the enzyme that starts the manufacture of serotonin from tryptophan. As a result, these rats never get the message to stop eating until they have consumed far greater amounts of food than normal rats.
There is much circumstantial evidence that many humansare genetically predisposed to obesity. This predisposition may involve the same mechanism as that observed in rats genetically predisposed to obesity. In other words, many people may be predisposed to being overweight because they have a decreased conversion of tryptophan to 5-HTP and, as a result, decreased serotonin levels. By providing preformed 5-HTP, this genetic defect is bypassed and more serotonin is manufactured. 5-HTP literally turns off hunger.
The early animal studies that used 5-HTP as a weight loss aid have been followed by a series of four human clinical studies of overweight women, conducted at the University of Rome. The first study showed that 5-HTP was able to reduce caloric intake and promote weight loss despite the fact that the women made no conscious effort to lose weight. The average amount of weight loss during the five-week period of 5-HTP supplementation was a little more than 3 pounds.
The second study sought to determine whether 5-HTP helped overweight individuals adhere to dietary recommendations. The twelve-week study was divided into two six-week periods. For the first six weeks, there were no dietary recommendations; for the second six weeks the women were placed on a 1,200-calorie diet. As shown in Table 1, the women who took the placebo lost 2.28 pounds, while the women who took the 5-HTP lost 10.34 pounds.
As in the previous study, 5-HTP appeared to promote weight loss by promoting satiety—the feeling of satisfaction—leading to fewer calories being consumed at meals. Every woman who took the 5-HTP reported early satiety.
In the third study involving 5-HTP, for the first six weeks there were no dietary restrictions, and for the second six weeks the women were placed on a 1,200-calorie-per-day diet. The results from this study were even more impressive than the previous studies for several reasons. The group that received the 5-HTP had lost an average of 4.39 pounds at six weeks and an average of 11.63 pounds at 12 weeks. In comparison, the placebo group had lost an average of only 0.62 pounds at six weeks and 1.87 pounds at twelve weeks. The lack of weight loss during the second six-week period in the placebo group obviously reflects the fact that the women had difficulty adhering to the diet.
Early satiety was reported by 100 percent of the subjects during the first six-week period. During the second six-week period, even with severe caloric restriction, ninety percent of the women taking 5-HTP reported early satiety. Many of the women who received the 5-HTP (300 mg three times per day) reported mild nausea during the first six weeks of therapy. However, the symptom was never severe enough for any of the women to drop out of the study. No other side effects were reported.
In the latest study, 25 overweight non-insulin dependent diabetic outpatients were enrolled in a double-blind, placebo-controlled study, and randomized to receive either 5-HTP (750 mg/d) or placebo for two consecutive weeks, during which no dietary restriction was prescribed. Results again indicated that patients receiving 5-HTP significantly decreased their daily energy intake, by reducing carbohydrate and fat intake, and reduced their body weight.
While these studies used relatively high dosages, my feeling is that lower dosages (e.g., 100 mg twenty minutes before meals) are just as effective (especially from a cost perspective).