The goal of this trial is to investigate the biological effects of oral supplementation with indole-3-propionic acid (IPA) taken twice daily in healthy adults. The main scientific questions are: * Does supplementation with IPA increase the abundance of regulatory T cells in the blood? Regulatory T cells are believed to play an important role in preventing autoimmune diseases. * Does supplementation with IPA increase the concentration of brain-derived neurotrophic factor (BDNF) in the blood? BDNF is believed to play an important role in maintaining brain health. * Does supplementation with IPA affect blood analyses commonly performed to assess the risk of metabolic disorders like type 2 diabetes and cardiovascular diseases? Participants will: * Take capsules to achieve a total daily dose of 1000 mg of IPA or placebo: 500 mg every morning and 500 mg every evening for 14 days. * Visit the clinic at the beginning (day 1) and at the end (day 15) of the supplementation period to deliver blood, urine and fecal samples, have simple measurements performed, fulfil questionnaires and report any side effects.