Effect of sugar, protein and fat rich diet on cumulative food intake and brain serotonin metabolism in rats

Central 5-hydroxytryptamine (5-HT; serotonin) system plays a key role in the regulation of eating behaviour, cerebral level of serotonin in animal models is inversely related to food intake and body weight. The present study concerns the effects of long-term consumption of sugar, protein and fat rich diet on food intake, growth rate and brain 5-HT metabolism in rats. The study was conducted on 24 male albino Wistar rats. Rats were divided into three groups, and each group was given a different macronutrient-specific diets including carbohydrate-, protein-, and fat-rich diets. Sugar, protein and fat rich diet were prepared by mixing standard rodent diet with table sugar, minced beef and beef fat in the ratio of 2:1 (w/w) respectively. Control rats were fed freely on standard rodent diet whereas the three test group rats were fed freely on their respective diet for 5 weeks. Cumulative food intakes and growth rates were monitored weekly. After 5 weeks of treatment, animals were decapitated to collect the brain samples for the analysis of tryptophan (TRP), 5-HT and 5-Hyroxyindoleacetic acid (5-HIAA) by HPLC-EC. After 5 weeks of treatment, growth rates were significantly decreased (p less than 0.01) in sugar rich diet treated rats and not altered in protein and fat rich diet treated animals. Brain 5-HT levels were significantly decreased in sugar (p less than 0.05) and protein (p less than 0.01) rich diet treated rats and significantly increased (p less than 0.05) in fat rich diet treated rats. Brain 5-HIAA and TRP levels were significantly decreased following the intake of sugar (p less than 0.05), protein (p less than 0.01) or fat (p less than 0.01) rich diet. Results showed that ingestion of sugar rich diet induced hyperphagia while ingestion of protein and fat rich diet induced hypophagia. The findings are discussed in the context of a role of serotonin in the regulation of appetite.