L-tryptophan is an essential amino acid and an essential component of the human diet. Thus, tryptophan supplements are of great importance nowadays.
Proven Effects of Tryptophan Supplements
Tryptophan plays an important role in many metabolic functions. Clinicians use information about tryptophan levels to diagnose various metabolic disorders and symptoms of associated diseases.
But what are the effects of tryptophan supplements? Let’s see!
Tryptophan and Nervous System
The addition of this amino acid to the diet is seen as a treatment for depression and sleep disorders, mainly because tryptophan is linked to the synthesis of serotonin (the hormone of joy) and melatonin (the hormone of sleep).
In addition, tryptophan supplements are used as an adjunct to help treat cognitive impairment, depression, or neurodegenerative diseases.
Decreased serotonin secretion, in turn, is associated with an autism spectrum disorder, obesity, anorexia, and bulimia nervosa, as well as other diseases presenting symptoms of peripheral diseases.
The literature strongly suggests that tryptophan plays a significant role in the proper functioning of the brain-intestinal axis and immunology.
Available information allows tryptophan to be considered an important dietary component because of its role in the serotonin pathway .
The daily dietary intake of tryptophan is recommended by WHO at 4 mg/kg (1/2 to 2 g per day).
In addition, it is important to know that the supply of tryptophan to the brain depends on the amount of free tryptophan in the blood and on the concentration of other amino acids (e.g., BCAAs) that compete with tryptophan for transporters used to cross the blood-brain barrier.
The enzyme tryptophan hydroxylase, which catalyzes the conversion of tryptophan to 5-hydroxytryptophan (5-HTP), can be inhibited by various factors, such as stress, insulin resistance, vitamin B6 deficiency, or magnesium deficiency.
For this reason, magnesium and vitamin B6 are often used together for disorders of the nervous system. Their deficiency prevents tryptophan from converting to 5-HTP and, subsequently, to serotonin .
Tryptophan as a Precursor to Serotonin
Tryptophan is the only precursor to the neurotransmitter serotonin.
Supplemental tryptophan consumption can boost serotonin neurotransmission to produce therapeutically important effects and eliminate serotonin deficiency.
Anorexia nervosa (AN) – an eating disorder associated with a high rate of psychiatric comorbidity, including psychosis, hyperactivity, depression, and anxiety, has the highest mortality rate of all psychiatric diseases.
Evidence suggests that excessive dietary intake and food restriction can decrease tryptophan and, thus, serotonin levels in the brain in patients, causing depression, psychosis, and hyperactivity.
In general, depressed patients have been found to be deficient in tryptophan relative to healthy subjects.
Two interventional studies that examined the effect of L-tryptophan or 5-HTP supplementation on depression found that both tryptophan and 5-HTP were superior over placebo in relieving depressive symptoms .
In one study, the subjects were male patients with alcoholism and associated depression and sleep disturbances. Subjects who took 3 g of L-tryptophan per day for 4 days reported much lower levels of depression than participants who received a placebo .
Effects of Tryptophan Supplements on Sleep
The earliest experimental results convincingly demonstrated the sleep-inducing effects of L-tryptophan in doses of 1 to 15 g at bedtime.
But a later laboratory study broadened the dose-response curve, comparing even smaller doses of 1/4, 1/2, and 1 g of L-tryptophan versus placebo in 15 subjects with moderate insomnia (sleep delay> 30 minutes).
One gram of L-tryptophan significantly decreased sleep latency, but lower doses tended in the same direction. Sleep stage IV was significantly increased by 1/4 g of L-tryptophan at bedtime.
Thus, an effective dose of tryptophan supplements taken before bedtime can be in the range of 1 gram .
Effect of Tryptophan Supplements on Appetite
Gut hormones such as cholecystokinin and glucagon-like peptide-1 (GLP-1) act as saturation factors. Strategies for increasing the secretion of satiety hormones can provide a therapeutic approach to the treatment of obesity.
One study examined the role of 0.52 g and 1.56 g of tryptophan taken orally on the secretion of these hormones in non-diabetic individuals. At a higher dose, L-tryptophan stimulated the release of cholecystokinin, induced a significant delay in gastric emptying, and caused a slight increase in GLP-1 secretion .
In another study in normal and overweight men, 3 g of tryptophan consumed 15 minutes before a carbohydrate meal reduced postprandial blood glucose by slowing gastric emptying .
Later experiments showed that tryptophan taken in the range of 1-1.5 g affects intestinal motility and its hormonal function, significantly reducing energy consumption. The strong inverse correlation between energy intake and L-tryptophan in plasma suggests that, in addition to gut mechanisms, the direct effects of circulating L-tryptophan also mediate its inhibitory effect on food intake .
Another interesting study linked amino acid intake to large-scale changes in brain networks involved in the regulation of metabolism. A direct link between saturation hormones and brain regions involved in the regulation of metabolism was confirmed by a positive correlation between brain activity in the islet cortex and insulin levels in blood plasma after oral administration of L-tryptophan (within 1 g).
Consuming L-Tryptophan (or L-Leucine) directly affected specific brain networks that support the food-reward system and appetite regulation .
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