L-Tryptophan is Reduced While Dieting - Does This Make the Essential Amino Acid a Key to Successful Weight Loss?
|Trp and it's metabolite 5-HTP may be particularly useful for female sugar cravings and binges.|
As Strasser et al. point out, both overweight and obesity go hand in hand with significant increases in low-grade inflammation. The latter is not just the reason that obesity increases the risk of cardiovascular disease, though. Recent evidence suggests that it is also associated with errors in the kynurenine (Kyn) pathway, in which tryptophan is broken down to kynurenine which in turn has been associated with increased risk of depressive symptoms, cognitive deficits in schizophrenia, Alzheimer's and, as mentioned before, cardiovascular disease. Weight loss, on the other hand,
"[...] has been shown to improve or prevent many of the aforementioned conditions. Bariatric surgical intervention in patients with adiposity was found not to improve tryptophan breakdown rates and other signs of immune activation and inflammation , whereas caloric restriction is known to be a strong activator of protective metabolic pathways, thereby leading to lower blood pressure, improved blood lipids, and reduced inflammatory markers, including CRP . Still, little is known about the effects of an extreme short-term hypocaloric diet on Trp metabolism and changes in inflammatory biomarkers" (Strasser. 2014).The study Barbara Strasser, Ken Berger and Dietmar Fuchs conducted was thus designed to assess the effect of a 2-week caloric restriction weight loss diet on Trp breakdown, leptin, and inflammatory biomarkers in over weight adults.
|Taking tons of BCAAs can deplete your brain Trp and serotonin and leave you tired and depressed.|
- a very low kcal diet group (VLCD; Ø 600 kcal/ day) and
- a low kcal diet group (LCD; Ø 1,200 kcal/day).
|Figure 1: Changes in body composition pre- vs. post (Strasser. 2015).|
In contrast to what the researchers expected, both the Trp and Kyn concentrations decreased significantly by 21 and 16 % for VLCD and by 15 and 17 % for the LCD group, respectively, with no significant difference between groups. Practically speaking, this means that the ratio of Kyn/Trp concentrations did not change significantly in both groups.
"Data for biologic markers are shown in Table . Fasting blood glucose declined significantly (P < 0.05) in the LCD group with no significant changes in insulin sensitivity in both groups after 2 weeks of caloric restriction. Weight loss diet lowered leptin levels in both groups, although not reaching the level of significance. Inflammatory biomarkers were not significantly altered during the trial, although there was a tendency toward an increase in IL-6 and TNF-a in the LCD group" (Strasser. 2015).
Table 1: Biologic markers before and after a 2-week very low kcal diet (VLCD) or low kcal die (LCD) in 38 overweight subjects (mean ± SD)
|Adding 900mg 5-HTP to the diet of obese women helps them to reduce their energy intake significantly (Cangiano. 1992).|
"Trp concentrations decreased significantly with a caloric restriction weight loss diet, and lowest Trp concentrations were observed in the group of individuals with the lowest calorie intake." (Strasser. 2015)This reduction in Trp levels may well induce a disturbance in the biosynthesis of neurotransmitter 5-hydroxytryptamine (5-HT | Anderson. 1990), and appears to be associated with an increased susceptibility for depression (Widnet. 2002; Raison. 2009). Strasser et al. highlight:
Experiments in which Trp was acutely depleted (in many studies by administering BCAAs | see red boy) support this assumption. Young et al. (2013), for example, confirmed that the acute depletion of tryptophan will lead to low serotonin and subsequently lower mood and increased aggression, although results vary somewhat between studies with similar participants.
"Because Trp is precursor in various biochemical pathways, e.g., it is hydroxylated by tryptophan-5-hydroxylase (T5H) into the intermediate product 5-hydroxy-tryptophan, which by decarboxylation is further converted to neurotransmitter 5-HT (serotonin), and because substrate saturation of T5H is only about 50 % (Dantzer. 2011), changes in plasma Trp levels may have an immediate impact on brain serotonin levels" (Strasser. 2014).
Figure 2: The consumption of tryptophan-free amino acid supplements leads to highly significant increases in hunger ratings in healthy female subjects (Rieber. 2010).
|Figure 3: Correlations between changes in tryp:LNAA ratio and appetite ratings (Gendall. 2000).|
Ah, and in case you are asking yourself why carbohydrate / sugar binges are a common consequence of low tryptophane:LNAA ratios, it's important to know that increases in glucose and insulin in response to high carbohydrate meals will trigger an increase in brain tryptophan and serotonin synthesis (Benton. 2002). This is why the effects of low tryptophan or high LNAA (BCAA, tyrosine, phenylalanine) levels are more pronounced if you avoid dietary carbohydrates.
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