Tryptophan administration may enhance weight loss by some moderately obese patients on a protein‐sparing modified fast (PSMF) diet

Drugs thought to enhance serotonin-mediated neurotransmission have been shown to diminish appetite for carbohydrates. Therefore, we examined the ability of tryptophan (TRP), serotonin's amino acid precursor, or a placebo to influence weight loss among 62 obese Swiss outpatients who were on a reducing diet [the Protein-Sparing Modified Fast (PSMF) Diet] which can be associated with severe carbohydrate craving. This diet provides relatively large amounts of protein (1.2–1.4 g/kg ideal body weight/day) but little carbohydrate (40 g/day or less), thus stimulating ketone body production. Its consumption also reduces the ratio of plasma TRP to the summed concentrations of the other large neutral amino acids, thereby probably diminishing brain TRP and serotonin levels. During the initial month of the PSMF diet all patients received the placebo; thereafter 30 received TRP (750 mg, twice daily, orally, for 3 months) and 32 the placebo, according to a double-blind protocol. Among moderately obese patients (140–159% of ideal weight; n = 25), the TRP significantly enhanced weight loss (p lt;.05), especially during the first treatment month (3.4 ± 2.8 vs 7.7 ± 1.7 kg lost; means ± standard deviation) but also during the total 3-month test period (2.6 ± 2.3 vs 1.5 ± 1.6 kg lost/month). The JRP didn't modify the reported adherence to the PSMF diet. The partial efficacy of TRP among our moderately obese subjects does not presently justify its routine use as an adjunct to a PSMF diet. However, greater efficacy may be obtained with better patient selection and under metabolic conditions designed to amplify the uptake of TRP into the brain (i.e., administration along with a carbohydrate).