The purpose of this study is to determine whether a diet intervention (the Fasting Mimicking diet) will help induce clinical and biochemical response to tofacitinib therapy or second line biologic therapy with ustekinumab or infliximab in patients with ulcerative colitis. Study period will be 8 weeks during induction of tofacitinib or ustekinumab or infliximab. The primary aims of this study are to determine clinical response and improvement in fecal calprotectin and C-reactive protein levels. Secondary outcomes will include assessment of changes in the stool microbiome.