Tryptophan

Tryptophan is an essential amino acid whose metabolites, particularly serotonin, are necessary for growth and development but become pro-inflammatory and degenerative when present in excess after maturity. 2 Peat argued that while tryptophan is indispensable during rapid growth, its continued high intake in adulthood allows its excitable, oxidative properties to act as random, excitatory, inflammation-promoting processes throughout the organism. 8 He identified tryptophan, along with cysteine and methionine, as a primary anti-thyroid amino acid that suppresses metabolism and contributes directly to the aging process. 2

The primary danger of excess tryptophan lies in its conversion to serotonin, a molecule Peat characterized as a central mediator of stress, inflammation, and learned helplessness. 9 Serotonin suppresses mitochondrial respiration, promotes lipid peroxidation and blood clotting, and stimulates the release of ACTH and cortisol, creating a self-perpetuating catabolic state. 3 Peat noted that estrogen redirects tryptophan metabolism toward serotonin, making women particularly susceptible to its negative effects, and that hypothyroidism and cortisol both increase serotonin formation. 2 In contrast, adequate vitamin B6 and calcium help direct tryptophan metabolism away from serotonin and toward the synthesis of niacinamide. 2

Restriction of tryptophan has been shown to produce profound anti-aging effects. Peat cited studies where rats fed a diet lacking tryptophan or containing only one-fourth the normal amount maintained reproductive ability far longer and experienced significant increases in both average and maximum lifespan, looking and acting like younger animals. 1 Georgi Dinkov has written that tryptophan is the only amino acid that is directly carcinogenic, likely through its ability to mimic estrogen in promoting prolactin release, and noted that it is always present in the smallest amounts in living organisms, indicating its potentially dangerous nature. 2 Dinkov also emphasized that tryptophan restriction, especially when combined with methionine and cysteine restriction, can increase maximum lifespan by 20 to 30 percent, dwarfing the effects of caloric restriction alone. 4

Peat recommended that adults limit their intake of tryptophan-rich foods, particularly muscle meats, which also contain high levels of pro-inflammatory cysteine, methionine, iron, and phosphate. 2 He advocated for the use of gelatin as a major dietary protein after growth is completed because it completely lacks tryptophan, cysteine, and methionine, thereby reducing the risk of inflammatory and degenerative diseases. 8 He warned that overconsumption of meat protein can displace carbohydrate in the diet and liberate thyroid-suppressing amino acids, noting that Broda Barnes had to double his thyroid dose when eating a high-meat diet. 6 The fatigue of over-training is likely produced by a tryptophan and serotonin overload resulting from muscle catabolism, and stress-induced free fatty acids increase tryptophan uptake into the brain, further driving serotonin synthesis. 2