Circulating ghrelin and GLP-1 are not affected by habitual diet

Abstract

Background: Ghrelin and glucagon-like peptide-1 (GLP-1) are gut hormones known to induce hunger and satiety, respectively. Current knowledge about the effects of different macronutrients on circulating ghrelin and GLP-1 comes mainly from acute test meals, whereas little is known about the effects of chronic dietary intake on gut hormone secretion. This study was designed to examine whether 8-week habituation to diets with different percentages of carbohydrate and fat would affect serum ghrelin, GLP-1, and subjective hunger in a postabsorptive state and in response to a standard liquid mixed meal.

Methods: Sixty-one overweight men and women were provided all food for 8 weeks of either a higher-carbohydrate/lower-fat diet (High-CHO/Low-FAT; 55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (Low-CHO/High-FAT; 43% CHO, 18% PRO, 39% FAT). After overnight fasts at baseline and week 8, participants consumed a standard liquid meal (7 kcals/kg, 58.6% CHO, 17.4% PRO, 24% FAT). Blood was sampled before the meal and at 15, 60, 90, 120, 180, and 240 min to determine total serum ghrelin and active GLP-1. Hunger was assessed by a visual analog scale. Mixed models were used to evaluate whether the temporal patterns of total serum ghrelin and active GLP-1 differed with diet.

Results: Although both diet groups reported greater hunger after 8 weeks (p=0.03), circulating ghrelin and GLP-1 were not affected by acclimation to different macronutrients.

Conclusion: Habituation to different diets does not appear to influence fasting ghrelin, fasting GLP-1, or responses of these gut hormones to a standard meal.

Figure 1

Time courses for total serum ghrelin. Ghrelin changed across the minutes of each meal test (p<0.001 for both). The higher-CHO/lower-FAT group had lower ghrelin at baseline and week 8 (p<0.001 for Diet Group), but p-values were not significant for change over 8 weeks or Diet x Week interaction.

Figure 2

Time courses for serum GLP-1. Changes from fasting values across the 4 hours of testing were greater at the 8-week test (p=0.030) compared to the 0-week test (p=0.155). There were no significant differences for Diet Group, Week, or Diet x Week interaction.

Figure 3

Time courses for subjective hunger. Hunger changed across the minutes of each meal test (p<0.001 for both). There were no significant differences for Diet Group or Diet x Week interaction, but both diet groups reported greater hunger at week 8 compared to week 0 (p=0.032 for Week).