The understanding of the relationship between diet composition and obesity is a current topic. Although satiety is controlled by many factors, hormones implicated in the control of food intake and glucose metabolism should be considered. The aim of this study was to compare the effect of two meals with different protein-to-fat ratios on fasting and postprandial plasma glucose, ghrelin, insulin, and amylin concentrations. 14 neutered cats were fed a high protein low fat (HPLF--48% energy from protein, 28% from fat) diet and a low protein high fat (LPHF--28% energy from protein, 46% from fat) diet in a randomized cross-over design. Cats were categorized according to their body fat mass (BFM) (p<0.001): group NO: BFM<30%, normal cats (n=5); group OB: BFM>31% obese cats (n=9). For each diet there was a 6-week adaptation period before the test meal. They were offered 70g/d. Blood samples for hormone assays were collected at the end of the 6-wk period before the meal (fasting) then immediately (T0), 30, 60 and 100 minutes after the test meal (35 g food/10 minutes) (post-prandial--pp). Commercially available kits previously validated for use in cats were used. Since data were non-normally distributed, non-parametric tests were used to examine the effects of diet and BFM. Values of p < 0.05 were considered significant.
Mean body weight did not differ between groups and during the study. Spontaneous food intake (g/d) did not differ between diets but total energy intake (kcal ME/d), energy (kcal ME) per kg BW or per kg fat-free mass were higher for LPHF diet (respectively p=0.014, p=0.013 and p=0.013). There was no effect of BFM on these parameters. Fasting glucose and hormone concentrations were affected by neither the type of diet or BFM. The HPLF diet induced greater pp variations of insulin (p=0.033) and amylin (p=0.035) than the LPHF diet and, inversely, changes in pp glucose were higher with the LPHF diet (p=0.001). Post-prandial variations of ghrelin were not affected by the composition of the meal. Unexpectedly, BFM had no effect on post-prandial insulin and amylin. However, time course of pp glucose was higher in obese cats than in lean cats (p<0.001). Moreover, change in pp ghrelin was significantly affected by BFM (p=0.019): pp ghrelin decreased in lean cats while it increased in obese cats.
The study showed an effect of the diet composition on post-prandial changes in glucose, insulin and amylin plasma concentration. The HPLF diet induced a higher post-prandial secretion of insulin and amylin than the LPHF diet suggesting a direct effect of amino acids on insulin secretion. Ghrelin was not affected by the type of diet suggesting a limited effect of the composition of the diet on satiety. Unexpectedly, the most marked effect on ghrelin secretion was related to body composition suggesting a dysregulation of food intake in obese cats unrelated with food composition.