Effects of small intestinal L-phenylalanine infusions on gut motility, gut hormone release and blood glucose control in humans.

INTERVENTION: There is increasing evidence that nutrient stimuli in the gut, especially in the small intestine, induce changes in gut motor and hormonal functions that play a central role in the control of energy intake and blood glucose. In particular high‐protein diets have been found to be very effective for weight loss and for improving blood glucose in obese with and without type 2 diabetes. This study aims to investigate the effects of the amino acid, L‐phenylalanine on gut motility, gut hormone release, blood glucose control and energy intake in humans. We hypothesise that L‐phenylalanine, as building block of proteins, may substantially contribute to the beneficial effects of whole protein on gut functions and energy intake regulation. A total of 20 Caucasian male and female (BMI 18‐25 kg/m2) subjects, aged between 18 ‐ 50 years, will be included in the study. Each subject will be studied on three occasions. On each occasion, they will receive, in randomized, double‐blind fashion, a 90‐min intraduodenal infusion of (i) L‐phenylalanine at 0.2 kcal/min (4.4 g/90 min), (ii), L‐phenylalanine at 0.4 kcal/min (8.8 g/90 min) or (iii) saline (negative control). Gut motility, blood glucose, gut hormones release, insulin concentrations, appetite perceptions and energy intake during a buffet meal, as well as vital signs, will be measured. The buffet meal will be provided at the end of the infusion and the participant has 30 minutes to eat until comfortably full. The buffet meal consists of 300ml orange juice, 600ml water, 375ml iced coffee, 4 slices white bread, 4 slices brown bread, 100g deli leg ham, 100g virginian chicken, 4 slices cheese, 100g tomato, 100g cucumber, 100g lettuce, 2 portions manyonnaise, 2 portions margarine, 1 medium apple, 1 medium banana, 200g chocolate custard, 150g fruit salad, 200g strawberry yoghurt, and 14g milky way chocolate bar. Each volunteer will receive one of each infusion solutions on each of the 3 study days. Each study visit will be separated by no less than 3 days. CONDITION: Healthy Human Physiology Obesity PRIMARY OUTCOME: Antropyloroduodenal motility (number of antral, duodenal and isolated pyloric pressure waves, and basal pyloric pressure) Plasma concentrations of gastrointestinal hormones (e.g. CCK, GLP‐1, PYY, GIP and ghrelin), insulin and glucose SECONDARY OUTCOME: Appetite sensations using a Visual Analogue Scale (VAS) (satiety, hunger, fullness, thirst, desire to eat and amount of food desired to eat) and macronutrient and total energy intake at the buffet meal INCLUSION CRITERIA: Male and female (BMI 18 to 25 kg/m2) subjects, aged between 18 to 50 years, will be included in the study. All subjects will be required to be weight‐stable (ie less than 5 % fluctuation in their body weight) at study entry, as determined by their self‐reported weight in the preceding 3 months, and will be required to maintain their normal physical activity over the course of the study.