To maintain a quiescent gut microenvironment, proper regulation of immune responses initiated by pro-inflammatory immune subsets is required. Several types of regulatory T cells are reported to exert pivotal roles in achieving this. Among various types of regulatory T cells, the crucial role of Foxp3+ Treg cells has been well documented. Furthermore, accumulating evidence demonstrates that both microbial and dietary factors influence the induction and suppressor functions of intestinal Foxp3+ Treg cells. Foxp3+ Treg cells are a highly activated T cell subset which responds rapidly to environmental and nutritional stimuli. Thus, sufficient nutrient supply is required to fuel the high energetic status of Foxp3+ Treg cells for the regulation of intestinal immunity.