Dietary casein has a higher potential than cod and pork to induce weight loss in obese C57BL/6J mice
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OBJECTIVE: In the western world, a high energy intake combined with limited physical activity have resulted in an obesity epidemic. Challenges associated with this is an altered glucose homeostasis, increased risk of several diseases and economical concerns. A high proportion of dietary protein is known to induce weight loss, but little attention is given to effects of different protein sources. We aimed to investigate the weight reducing effect of low-fat diets enriched with the different protein sources casein, cod and pork. RESEARCH DESIGN AND METHODS: An animal study was conducted, using C57BL/6J mice. Obesity was induced, by giving the animals a very high fat (VHF) diet. Three groups (n=10) were given a low fat diet (15 E% from fat, 16 E% from protein, 57 E% from carbohydrates, 12 E% from sucrose) and one group continued on a VHF control diet (52 E% from fat, 16 E% from protein and 32 E% from carbohydrates). Feed intake was recorded and an OGTT and ITT was performed after 3 weeks of experimental feeding. Plasma insulin levels were measured using ELISA, and mRNA levels of genes were measured using qPCR. Histological sections were exposed to both H&E and immunohistochemical staining. Data from an earlier completed experiment was included, following the same design, only with 30 % energy restriction. RESULTS: Mice fed casein had the greatest loss of body weight and fat mass, but the cod - fed mice obtained the highest lean mass. Protein from casein also seem to improve glucose tolerance and insulin sensitivity in the mice, compared to cod and pork. However, when fed ad libitum a modest change was seen. Furthermore, our results show a significantly lower energy intake in the cod-fed mice. Sections of interscapular brown adipose tissue (iBAT) from the different groups indicate a higher degree of multilocular cells in iBAT from casein-fed mice in addition to a higher Ucp1 expression. Possible mechanisms to elucidate the findings are explored and discussed. CONCLUSIONS: The results herein indicate that feeding obese mice a diet with casein decreases body weight and improves glucose and insulin homeostasis to a greater extent than a diet with cod or pork. Research suggests that casein can mimic the beneficial effects of a high-protein diet, compared to other protein sources. Further research is necessary to demonstrate whether these findings are of relevance to human nutrition.