An increasing number of studies indicate that dairy products, including
whey protein, alleviate several disorders of the
metabolic syndrome. Here, we investigated the effects of
whey protein isolate (whey) in mice fed a high-fat diet hypothesising that the metabolic effects of whey would be associated with changes in the gut microbiota composition. Five-week-old male C57BL/6 mice were fed a high-fat diet ad libitum for 14 weeks with the
protein source being either whey or
casein. Faeces were collected at week 0, 7, and 13 and the fecal microbiota was analysed by denaturing gradient gel electrophoresis analyses of PCR-derived
16S rRNA gene (V3-region) amplicons. At the end of the study, plasma samples were collected and assayed for
glucose,
insulin and
lipids. Whey significantly reduced
body weight gain during the first four weeks of the study compared with
casein (P<0.001-0.05). Hereafter
weight gain was similar resulting in a 15% lower final
body weight in the whey group relative to
casein (34.0±1.0 g vs. 40.2±1.3 g, P<0.001). Food intake was unaffected by
protein source throughout the study period. Fasting
insulin was lower in the whey group (P<0.01) and
glucose clearance was improved after an oral
glucose challenge (P<0.05). Plasma
cholesterol was lowered by whey compared to
casein (P<0.001). The composition of the fecal microbiota differed between high- and low-fat groups at 13 weeks (P<0.05) whereas no difference was seen between whey and
casein. In conclusion, whey initially reduced
weight gain in young C57BL/6 mice fed a high-fat diet compared to
casein. Although the effect on
weight gain ceased, whey alleviated
glucose intolerance, improved
insulin sensitivity and reduced plasma
cholesterol. These findings could not be explained by changes in food intake or gut microbiota composition. Further studies are needed to clarify the mechanisms behind the metabolic effects of whey.