REN and Hypertension: 3. Increasing phylum Firmicutes and reduction of Bacteroidetes were associated with maternal tryptophan supplementation. 4. Trp and CKDTrp interventions increased the Firmicutes to Bacteroidetes ratio compared with the control  Group. 5. Tryptophan is thought to prevent hypertension by controlling nitric oxide and the renin-angiotensin system pathways and modulating tryptophan-metabolizing microbes.