A comparative in vitro investigation into the effects of cooked meats on the human faecal microbiota

Protein fermentation is one of the important microbial activities in the human colon. Meat foods rich in protein provide substantial resource for this metabolic activity. However, little information exists on the relative impact of different meats on the composition and activities of the human gut microbiota. Similarly, little information is available on the confounding effects of cooking on these activities. In this study, beef, chicken and fish (salmon) were examined in vitro for their impact on the human faecal microbiota. The influence of cooking method was also investigated by using either frying or boiling. Upon fermentation over 48 h the Clostridium perfringens/histolyticum group increased significantly in number in the beef fermentations, either fried (p = 0.023) or boiled (p = 0.017). Cooking method appeared to influence Clostridium spp. growth, with higher numbers in fried meat compared to boiled meats after 5 h (p = 0.024) and 48 h (p = 0.003) fermentation. Significant differences between meat types were also seen for numbers of Bifidobacterium spp. at 48 h (p = 0.028), Bacteroides group at 24 h (p = 0.016) as well as Coriobacterium/Atopobium group at 10 h (p = 0.038). Most types of short chain fatty acids increased significantly in concentration over the experiment (p < 0.05). Significant differences between meat types were found in n-butyric acid production at 24, 30 and 48 h (p = 0.015, p = 0.024 and p = 0.035 respectively) and in i-valeric acid production at 10, 24, 30 and 48 h (p = 0.026, p = 0.002, p = 0.019 and p = 0.022 respectively). The concentration of i-valeric acid differed significantly between cooking methods at 24 h (p = 0.042). These findings suggest that both the type of meat and cooking process can influence fermentation profiles within the human gut microbiota. Interactions between ingested cooked meats and the gut microbiota may represent a novel corollary to mechanisms underlying the observed increased risk of intestinal and systemic diseases associated with high intake of certain meats/processed meats.