Suppression of Energy Intake by Intragastric l-Tryptophan in Lean and Obese Men: Relations with Appetite Perceptions and Circulating Cholecystokinin and Tryptophan.
- 2021-10
- The Journal of nutrition 151(10)
- Maryam Hajishafiee
- Sina S Ullrich
- Penelope Ce Fitzgerald
- Michael Horowitz
- Kylie Lange
- Sally D Poppitt
- Christine Feinle-Bisset
- PubMed: 34255069
- DOI: 10.1093/jn/nxab218
Study Design
- Type
- Randomized Controlled Trial (RCT)
- Sample size
- n = 13
- Population
- 12 lean men (mean ± SD age: 30 ± 3 y; BMI: 23 ± 1) and 13 men with obesity (mean ± SD age: 31 ± 3 y; BMI: 33 ± 1)
- Methods
- double-blind, randomized, intragastric administration of 3 g or 1.5 g L-tryptophan or control, 30 min before a buffet-meal
- Blinding
- Double-blind
- Funding
- Unclear
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.Research Insights
Trp alone increased plasma CCK, Trp, and the Trp:LNAAs ratio (all P < 0.001), with no difference between groups.
- Effect
- Beneficial
- Effect size
- Small
- Dose
- 3 g (Trp-3) or 1.5 g (Trp-1.5)
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).
- Effect
- Neutral
- Effect size
- Small
- Dose
- 1.5 g (Trp-1.5)
Trp alone increased plasma CCK, Trp, and the Trp:LNAAs ratio (all P < 0.001), with no difference between groups.
- Effect
- Beneficial
- Effect size
- Large
- Dose
- 3 g (Trp-3) or 1.5 g (Trp-1.5)
Trp alone increased plasma CCK, Trp, and the Trp:LNAAs ratio (all P < 0.001), with no difference between groups.
- Effect
- Beneficial
- Effect size
- Large
- Dose
- 3 g (Trp-3) or 1.5 g (Trp-1.5)
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).
- Effect
- Beneficial
- Effect size
- Moderate
- Dose
- 3 g (Trp-3) or 1.5 g (Trp-1.5)
hunger, fullness, and plasma CCK and amino acid concentrations were measured ... No significant effect on hunger was explicitly reported as such; however, the abstract does not mention a significant effect on hunger. Since the outcome was measured and no significant effect is indicated, it is treated as neutral.
- Effect
- Neutral
- Effect size
- Small
- Dose
- 3 g (Trp-3) or 1.5 g (Trp-1.5)