The Effect of 5-Hydroxytryptophan (5-HTP) on Satiety

One of the physiological factors regulating the food intake pattern is satiety. Satiety is defined as the absence of ingestive motivation, which ends when the next meal is initiated (Blundell et al., 1996). Food intake affects a number of physiological objective parameters in blood known to be involved in signalling satiety, such as glucose (Melanson et al, 1999; Chapman et al, 1999; Campfield et al, 1996), insulin (Speechly et al, 2000) and cholecystokinin (CCK) (Gutzwiller et al., 2000; Beglinger et al., 2001; French et al., 2000; Degen et al., 2001; Burton-Freeman et al., 2002, 2004). More recently, the gastric hormone ghrelin was identified as a marker for hunger and meal initiation (De Graaf et al., 2004).

Humans do not only eat in response to a metabolic or physiological need. Humans also respond to a significant extent to other internal subjective and emotional signals (clues). The exact relations between the physiological internal signals and subjective and emotional internal signals are not known. Besides also external and social factors modulate physiological-derived hunger and satiety signals.

Though the regulation of food intake has been studied quite extensively, the underlying mechanism is not elucidated yet and still new factors involved in this regulation are being found. It is known that the macronutrients such as lipids, proteins and carbohydrates affect satiety differently, but this mechanism is still not very clear either.

Nowadays, more and more food supplements become available suggesting to affect hunger and satiety sensations, resulting in the long-term in weight loss. For example dietary fibres are known for their satiating effect.

The food supplement 5-HTP is used for this purpose as well. The food supplement, already available in the United States and in Italy, has been investigated for multiple indications such as migraine, depression, anxiety, fibromyalgia, hypertension, insomnia and obesity.

Different clinical studies have been performed with 5-HTP for more than three decades now. With respect to lowering of food intake, 5-HTP has been studied as well.

5-HTP is an amino acid produced by the human body from the essential amino acid L-tryptophan, which is found in food products. Its clinical value is the ability to increase production of serotonin. As a potentially valuable supplement it has been used clinically for more than 30 years. 5-HTP occurs naturally in two places - the human body and the seeds of the Griffonia simplicifolia, a West African medicinal plant.

5-HTP is the amino acid precursor of serotonin. Normal levels of serotonin are important for emotional well-being, may play a role in appetite suppression, and decreased carbohydrate and fat intake. Only free plasma tryptophan can cross the blood brain barrier via a carrier protein to enter the central nervous system (CNS). Once in the CNS, tryptophan is converted to 5-HTP and then is decarboxylated to serotonin. The levels, and possible function, of several neurotransmitters can be influenced by the supply of their dietary products. A reduction in tryptophan has been correlated to a reduction in serotonin (Curcio et al., 2005).

The 5-HTP metabolism is then influenced by plasma tryptophan levels, which are related to food intake. Serotonin synthesis is directly dependent on the availability of the specific precursor tryptophan and on the nutritional status.

The effect of 5-HTP intake on food intake and mood is based on the serotonin production. Numerous studies have shown that long-term consumption of 5-HTP (levels up to 900 mg daily) reduced food intake and resulted in weight loss.

In a previous study by Laboratoire Oenobiol with moderately overweight men aged 20-40 years, given 50 or 150 mg 5-HTP half an hour before lunch and half an hour before dinner, a reduced energy intake with 300 mg 5-HTP compared to placebo was found. This was supplied acutely on one day.

The study reported a linear dose related effect, with significant food intake inhibition effect with a 300 mg/day 5-HTP dose. The dose of 100 mg/day did not produce statistically significant effects compared to placebo. However, 100 mg of 5-HTP could prove to be sufficient if given under chronic administration conditions.

In the present study therefore subjects will be supplied with 100 mg 5-HTP daily for one week. Hunger and satiety feelings, food intake and wellness will be investigated. The study will be conducted with overweight women, assuming that this group of subjects will be the target group.