In a study done by Heraief, Burckhardt, Wurtman and Wurtman, (1985), they 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 known as the Protein-Sparing Modified Fast (PSMF) Diet which is often associated with severe carbohydrate craving. This diet provided relatively large amounts of protein but little carbohydrates, thus stimulating ketone body production. Its consumption also reduced the ratio of plasma TRP to the summed concentrations of the other large neutral amino acids, thereby probably diminishing brain TRP and serotonin levels. It was found that among moderately obese patients the TRP significantly enhanced weight loss, especially during the first treatment month but also during the total. The TRP didn't modify the reported adherence to the PSMF diet. The partial effectiveness of TRP among the moderately obese subjects did not 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. There is a wide-ranging consensus that the most critical factor in weight management is total energy intake. However the ideal balance of macronutrients for weight loss and adult weight management remains widely disputed. Often this debate center son the relative merits or risks of carbohydrates vs. lipids. When the energy amount of the diet is equal, the relative levels of carbohydrates and lipids in the diet appear to have minimal affect on either weight loss or body composition. There is a growing amount of evidence that diets with reduced levels of carbohydrates and higher levels of protein may be beneficial for weight loss. These studies have shown that diets with reduced carbohydrates and higher protein appear to increase weight loss, increase loss of body fat, or reduce loss of lean body mass. While there are potential benefits for higher protein diets during weight loss, a metabolic explanation for optimal levels of carbohydrates and proteins remains unknown (Layman and Baum, 2004).

Potential explanations for the beneficial effects of diets with higher protein and reduced levels of carbohydrates include lower energy intake associated with increased satiety, reduced energy efficiency or increased thermogenesis, sparing of muscle protein loss, and enhanced glycemic control. In a study done by Layman and Baum, (2004), their research focused on the role of amino acids in regulation of muscle protein metabolism and glycemic control. The role of protein in the diet is to make available the 20 naturally occurring amino acids and specifically to provide the 9 crucial amino acids. Each of these amino acids has a distinctive requirement as a building block for body proteins. Nonetheless, the dietary requirement is not tightly linked to substrate needs for protein synthesis. This study found that one cause for the lack of a direct relationship is the recycling of amino acids after degradation of existing proteins and Amino acids are efficiently reutilized for synthesis of new proteins

Plasma 42-amino-acid amyloid-? (a?42) levels appear to associate with BMI, according to a study done by Yong-Ho, Martin, Maple, Tharp and Pratley, (2009). They recently showed that adipocyte amyloid precursor protein (APP) expression is up regulated in obesity and correlates with insulin resistance and adipose tissue inflammation. In this study, they aimed to investigate the relation between adipocyte APP expression and plasma a? peptide levels. They carried out a pilot study in which we measured adipocyte APP gene expression and the circulating plasma levels of a?40 in 10 obese individuals before and after a 6-month behaviorally-based weight loss intervention. Subjects were given an oral glucose tolerance test with measurement of insulin levels, a?40 levels measured by ELISA and transcript levels of APP in subcutaneous abdominal adipocytes measured by quantitative real-time PCR. The results showed that at baseline, adipocyte APP expression correlated significantly with plasma a?40 levels and with 2-hour insulin concentrations. After the 6-month weight loss intervention, body weight and BMI decreased significantly (Yong-Ho, Martin, Maple, Tharp and Pratley, 2009).

In order to test the effect on satiety of a formulation comprising plant extracts that naturally containing 5-hydroxytryptophan, Rondanelli, Klersy, Iadarola, Monteferrario and Opizzi,( 2009), conducted a study in which they delivered a sublingual spray (5HTP-Nat Exts), administered five times a day for 2 months. This study looked at bioavailability of 5-hydroxytryptophan following sublingual delivery over 8 weeks, by comparing...

Additional secondary end points of the study were to compare body composition, depressive symptoms, severity of binge eating and quality of life. This study also looked at whether a single dose of 5HTP-Nat Exts in fasting state has an effect on amino-acid profile and on appetite ratings and whether 5HTP-Nat Exts administered before a fixed test meal has any effect on satiety. The results showed that the group using the 5HTP-Nat Exts experienced a significantly greater increase in their sensation of satiety over an 8-week timeframe and in fasting state following administration of 5HTP-Nat Exts than the placebo group did. All the amino acids assessed after a single administration of 5HTP-Nat Exts were found to be similar. Variations were found for the mean change in body mass index, skinfold thicknesses and hip circumference. All these findings advocate that 5HTP-Nat Exts may be safely used to treat the problem of appetite control in overweight women throughout a weight loss program (Rondanelli, Klersy, Iadarola, Monteferrario and Opizzi, 2009).
The role of dietary protein in weight loss and weight maintenance includes influences on crucial targets for body weight regulation, namely satiety, thermogenesis, energy efficiency, and body composition. Protein-induced satiety may be mainly due to oxidation of amino acids that are fed in excess. Protein-induced energy expenditure may be due to protein and urea synthesis and to gluconeogenesis which is when complete proteins having all essential amino acids show larger increases in energy expenditure than do lower-quality proteins. During weight loss, nitrogen intake positively affects calcium balance and consequent preservation of bone mineral content. Sulphur-containing amino acids cause a blood pressure which raises the effect by loss of nephron mass. In a study done by Westerterp-Plantenga, Nieuwenhuizen, Tome, Soenen and Westerterp, (2009), subjects with obesity, metabolic syndrome, and type-2 diabetes were found to be particularly susceptible. Their research showed how sustaining absolute protein intake affects metabolic targets for weight loss and weight maintenance during negative energy balance, such as sustaining satiety and energy expenditure and sparing fat-free mass, resulting in energy inefficiency. However, the long-term relationship between net protein synthesis and sparing fat-free mass remains to be explained.