Effects of intragastric tryptophan on acute changes in the plasma tryptophan/large neutral amino acids ratio and relationship with subsequent energy intake in lean and obese men

How we decide what to eat: Toward an interdisciplinary model of gut-brain interactions

Everyday dietary decisions have important short-term and long-term consequences for health and well-being. How do we decide what to eat, and what physiological and neurobiological systems are involved in those decisions? Here, we integrate findings from thus-far separate literatures: (a) the cognitive neuroscience of dietary decision-making, and (b) growing evidence of gut-brain interactions and especially influences of the gut microbiome on diet and health outcomes. We review findings that suggest that dietary decisions and food consumption influence nutrient sensing, homeostatic signaling in the gut, and the composition of the gut microbiome. In turn, the microbiome can influence host health and behavior. Through reward signaling pathways, the microbiome could potentially affect food and drink decisions. Such bidirectional links between gut microbiome and the brain systems underlying dietary decision-making may lead to self-reinforcing feedback loops that determine long-term dietary patterns, body mass, and health outcomes. This article is categorized under: Economics > Individual Decision-Making Psychology > Brain Function and Dysfunction Psychology > Reasoning and Decision Making.

Suppression of Energy Intake by Intragastric l-Tryptophan in Lean and Obese Men: Relations with Appetite Perceptions and Circulating Cholecystokinin and Tryptophan

BACKGROUND

l-Tryptophan reduces energy intake in healthy men. The underlying mechanisms, including appetite, plasma cholecystokinin (CCK), tryptophan (Trp), and the ratio of Trp to large neutral amino acids (Trp:LNAAs ratio), and whether responses differ in lean and obese individuals, are uncertain.

OBJECTIVES

We evaluated the effects of intragastric Trp on energy intake (primary outcome) and their potential mechanisms, pre- and postmeal, in lean men and those with obesity.

METHODS

Twelve lean men [mean ± SD age: 30 ± 3 y; BMI (in kg/m2): 23 ± 1] and 13 men with obesity (mean ± SD age: 31 ± 3 y; BMI: 33 ± 1) received, on 3 separate occasions, in double-blind, randomized order, 3 g ("Trp-3") or 1.5 g ("Trp-1.5") Trp, or control ("C"), intragastrically, 30 min before a buffet-meal. Energy intake from the buffet-meal, hunger, fullness, and plasma CCK and amino acid concentrations were measured in response to Trp alone and for 2 h postmeal. Data were analyzed using maximum likelihood mixed-effects models, with treatment, group, and treatment-by-group interaction as fixed effects.

RESULTS

Trp alone increased plasma CCK, Trp, and the Trp:LNAAs ratio (all P < 0.001), with no difference between groups. Trp suppressed energy intake (P < 0.001), with no difference between groups (lean, C: 1085 ± 102 kcal, Trp-1.5: 1009 ± 92 kcal, Trp-3: 868 ± 104 kcal; obese, C: 1249 ± 98 kcal, Trp-1.5: 1217 ± 90 kcal, Trp-3: 1012 ± 100 kcal). Postmeal, fullness was greater after Trp-3 than after C and Trp-1.5 (all P < 0.05), and in men with obesity than in lean men (P < 0.05). Plasma Trp and the Trp:LNAAs ratio were greater after Trp-3 and Trp-1.5 than after C (all P < 0.001), and tended to be less in men with obesity than in the lean (P = 0.07) (Trp:LNAAs ratio: lean, C: 1.5 ± 0.2, Trp-1.5: 6.9 ± 0.7, Trp-3: 10.7 ± 1.4; obese, C: 1.4 ± 0.1, Trp-1.5: 4.6 ± 0.7, Trp-3: 7.8 ± 1.3). There were inverse correlations of energy intake with plasma Trp and the Trp:LNAAs ratio in both groups (lean, both r = -0.50, P < 0.01; obese, both r = -0.40, P < 0.05).

CONCLUSIONS

Intragastric Trp has potent energy intake-suppressant effects, in both lean men and those with obesity, apparently related to the Trp:LNAAs ratio.

Dietary Tryptophan and the Risk of Metabolic Syndrome: Total Effect and Mediation Effect of Sleep Duration

PURPOSE

Tryptophan affects energy homeostasis, glucose metabolism, blood pressure, and sleep. However, studies investigating the association between tryptophan and metabolic syndrome (MetSyn) are rare. We aimed to investigate the associations of dietary tryptophan with MetSyn incidence and potential mediation via sleep duration.

METHODS

Data of 7890 participants were obtained from the China Health and Nutrition Survey (1997-2011) (male: 49.9%; mean age=43.43 years;median follow-up=129.76 months; MetSyn incidence: 16.3%). A combination of individual 24-hour recall and household survey was used to assess dietary intake. In total, 6720 and 4474 participants who reported sleep duration and had blood samples taken, respectively, were incorporated into subgroup analyses. MetSyn was defined according to National Cholesterol Education Program Adult Treatment Panel (NCEP ATP) III criteria (2004), and tryptophan consumption and sleep duration were assessed by self-report in each survey. Multivariate Cox regression models were used to assess the associations between tertiles of tryptophan intake and MetSyn. Generalized linear regression models were used to evaluate the effect of tryptophan on sleep duration and plasma biomarkers.

RESULTS

Dietary tryptophan showed a protective effect on the risk of MetSyn. The hazard ratio (95% CI) of MetSyn was 0.77 (0.65-0.90) for individuals with a high tertile of tryptophan. Sleep duration was significantly higher, and HbA_1c, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein B (APO-B) were lower in the high tertile of tryptophan compared to the low tertile (P<0.05). In addition, mediation effects on the association between tryptophan intake and MetSyn risk were observed for sleep duration (estimated mediation percentage: 26.5%).

CONCLUSION

Our study demonstrated a negative association between dietary tryptophan and MetSyn incidence, and the mediation effect of sleep duration on this association, after adjusting for numerous confounders such as nutrients and food patterns. These findings may have important public health implications for the improvement of cardiometabolic health.