Abstract

BACKGROUND: Fasting is one of the most cost-effective methods to improve cardiometabolic health. We tested a 5-day hypocaloric (~ 600 kcal/day) and ketogenic, modified fasting program (MFP) in a two-arm randomised controlled trial, where sixty-four healthy subjects were randomised to MFP or control group. METHODS: We randomly assigned 64 participants to a group receiving the MFP or to a group of participants who were told to continue with their usual eating behaviour and lifestyle (control group). The changes in blood pressure and body weight were considered as primary endpoints. Secondary outcomes included ketosis, glucose and lipid metabolism, inflammatory markers, antioxidant capacity and well-being. Biological pathways and metabolic processes were explored with nuclear magnetic resonance blood metabolomics and gut metagenomics analyses. Outcomes were assessed at baseline, end of the MFP, after food reintroduction, and one month later. RESULTS: MFP participants (n = 32) experienced weight loss compared to controls (- 0.52 +/- 0.03 kg vs. - 0.03 +/- 0.02 kg, p < 0.001). Changes in blood pressure caused by the MFP were non-significant at the end of the fasting period. However, blood pressure was significantly reduced following food reintroduction (systolic: -0.56 +/- 0.12 mmHg vs. - 0.16 +/- 0.12 mmHg, p < 0.05 and diastolic: -0.36 +/- 0.08 mmHg vs. - 0.01 +/- 0.08 mmHg, p < 0.01). Serum biochemistry showed the MFP reduced glucose levels and coagulation factors. The MFP also significantly increased physical well-being. Blood metabolomics revealed a significant decrease in chronic inflammation markers. Shotgun metagenomics of the gut microbiome showed significant changes in relative abundance of 11 bacterial species and in the genomic repertoire of 52 carbohydrate-active enzymes (CAZymes), reflecting an increase in families metabolising host-derived glycan substrates. None of these differences in gut microbiome and blood metabolome were shown to be statistically different from the control group one month after the intervention. Comparing MFP effects with a previous cohort’s 5-day prolonged fasting showed similar metabolic changes. CONCLUSIONS: This MFP is safe and transiently improves cardiometabolic health and physical well-being in healthy individuals. CLINICAL TRIAL REGISTRATION: This trial was prospectively registered at ClinicalTrials.gov (NCT05821660) on 6 April 2023 prior to the start of patient recruitment.