The Effect of Potato Protease Inhibitor II on Gastrointestinal Hormones and Satiety in Humans During Weight Reduction

Abstract

Context: It is questioned whether the potato protein protease inhibitor II (PI2) reduces appetite and exerts effects on the satiety hormone cholecystokinin (CCK).

Objective: To investigate PI2 impact on gastrointestinal hormones and appetite measures during weight reduction.

Design: In a randomized, placebo-controlled trial over 20 weeks, fifty-two overweight/obese participants (BMI 25.2-38.0 kg/m²) received a protein-rich diet (30%) adjusted to 500 kcal below their individual daily needs. Subjects ingested a capsule containing either PI2 (150 mg) or placebo twice daily 1 hr before lunch and dinner. At week 0 and week 10 participants joined breakfast test meals to determine CCK, GLP-1, ghrelin, leptin, glucose and insulin concentrations in a time course experimental manner. Appetite sensations were measured on test meal days and in week 4, 9, 14 and 19 using visual analogue scales.

Results: Weight loss at week 10 and 20 in the PI2 group was 4.3±3.1 kg and 5.6±4.1 kg, in the control group: 4.7±4.0 kg and 6.8±3.7 kg. A significant effect of PI2 on circulating CCK levels was observed at week 10. The other hormones were unaffected by PI2. At week 10, PI2 group subjects showed higher satiety and decreased desire to eat compared to placebo. During study duration, PI2 showed a significant impact on appetite ratings prior to lunch, one hour before dinner and just before dinner.

Conclusion: PI2 increased circulating CCK plasma levels during the diet intervention. Likewise, PI2 modulated appetite sensation from week 4 to 20. The study demonstrated that the PI2 can modulate a key satiety signal.

Keywords: appetite; dietary supplement; obesity; satiety modification.

Figure 1

Change of CCK (a), GLP-1 (b), ghrelin (c) and leptin (d) concentrations for a fasting and meal-stimulated time course experiment in patients who ingested PI2 (●) or placebo (○) one hour before the test meal (taken at time 0 min), at the beginning of the study (column A) and after 10 weeks of weight reduction (column B). *AUC p<0.05 postprandial hormone release.

Figure 2

Change of glucose and insulin concentrations for a fasting and meal-stimulated time course experiment of in patients who ingested PI2 (●) or placebo (○) one hour before the test meal (taken at time 0 min) at the beginning of the study (column A) and after 10 weeks of weight reduction (column B).

Figure 3

Absolute values of a fasting and meal-stimulated time course experiment analyzing CCK, GLP-1, ghrelin, leptin, glucose and insulin in patients who ingested PI2 one hour before the test meal (taken at time 0 min) at the beginning of the study (▲) and after 10 weeks of study duration (∆). *AUC p<0.01 hormone concentration after 10 weeks.

Figure 4

Subjective appetite ratings for satiety (a), hunger (b), desire to eat (c), and prospective consumption (d) in response to PI2 before and after a test meal (week 0 chart A, week 10 chart B). One hour before the test meal PI2 or placebo was taken; PI2 group (●), placebo group (○). Values are mean values ± SEM.

Figure 5

Changes in appetite ratings in response to PI2 for satiety (A), hunger (B), desire to eat (C) and prospective consumption (D). One hour before lunch (−60 min) and one hour before dinner (−60 min) PI2 or placebo was taken. VASs were completed in week 4, 9, 14, 19 and combined data of all weeks are shown; PI2 group (●), placebo group (○). Values are mean values ± SEM. *p < 0.0001, #p<0.05 PI2 vs GC at individual time points.