Exploring how pairing a nutrient-dense low-carb diet with a 10-hour eating window can enhance weight loss and reshape the gut microbiome in adults struggling with obesity.
Study: Effects of healthy low-carbohydrate diet and time-restricted eating on weight and gut microbiome in adults with overweight or obesity: Feeding RCT. Image Credit: Boontoom Sae-Kor / Shutterstock
In a recent study published in the journal Cell Reports Medicine, researchers assessed the effects of a 10-hour time-restricted eating (TRE) window and a nutritionally balanced, healthy, low-carbohydrate diet (HLCD) in obese/overweight adults.
Moderate calorie restriction (CR) is recommended for individuals with obesity; however, the potential additional benefits of specific dietary patterns, when combined with CR, remain unclear. While a low-carbohydrate diet (LCD) has shown favorable impacts on weight loss and cardiometabolic biomarkers, most trials on LCD have mainly focused on the quantity of macronutrients, often neglecting dietary quality and nutrient diversity.
Further, high-quality evidence on the health effects of an HLCD, which emphasizes whole, minimally processed sources of carbohydrates, unsaturated fats, and plant protein, remains limited. TRE has also been linked to cardiometabolic health and weight loss; however, studies assessing whether TRE confers unique or additional health benefits beyond CR have produced inconsistent results. Moreover, the metabolic effects of combining TRE and HLCD in a single intervention have not been fully explored.
Study Design and Key Findings
In the present study, researchers assessed the impact of both TRE and HLCD on the gut microbiome, key cardiometabolic biomarkers, and body weight. This randomized controlled feeding trial was conducted between March 2022 and April 2023, involving a 12-week intervention followed by a 28-week post-intervention follow-up. Ninety-six adults aged 20–60 with a body mass index (BMI) ≥ 24 kg/m2 were randomized equally into four treatment groups: HLCD alone, TRE alone, a combined TRE and HLCD group, and a control group.
During the intervention phase, isocaloric-restricted diets were provided to participants on five workdays. Participants in the combined HLCD and TRE group followed a 10-hour TRE window within the HLCD framework. The HLCD comprised 50%, 20%, and 30% of total energy from fats, proteins, and carbohydrates, respectively. TRE required participants to eat meals within a 10-hour window. The TRE group followed a traditional Chinese diet but adhered to the 10-hour eating window, while the HLCD group followed the HLCD without time restrictions. The control group, too, received the traditional diet and continued their usual eating regimens. The study's primary outcomes were changes in body weight, body composition metrics such as BMI, and fasting glucose levels.
Secondary outcomes included changes in the gut microbiome, cardiometabolic biomarkers, the fecal metabolome, and adverse events. Overall, 88 participants completed the intervention phase, and 79 attended the follow-up visit 28 weeks after the intervention. Baseline characteristics were comparable between groups.
The mean eating window achieved was 10.4 hours for the TRE group and 11.7 hours for the non-TRE group. Mild adverse events, such as constipation, fatigue, and gastrointestinal issues like diarrhea and dizziness, were reported during the trial. Average weight loss across groups at 12 weeks was 2.57 kg for controls, 3.78 kg for the TRE group, 3.7 kg for the HLCD group, and 4.11 kg for the combined TRE and HLCD group.
Body Composition and Metabolic Health Outcomes
The HLCD group exhibited greater reductions in BMI and fat mass compared to non-HLCD participants. In contrast, TRE led to a more significant reduction in hip circumference and soft lean mass than non-TRE participants. All intervention groups showed improvements in blood pressure, liver and kidney function, and total cholesterol after the 12-week CR, relative to baseline.
Further, fecal metagenomic sequencing was performed to examine gut microbiome changes. There were no significant differences in gut microbial diversity metrics (alpha or beta diversity) between groups at baseline. However, by the end of the intervention, a significant difference in beta diversity was evident in TRE and HLCD groups. While the Shannon index of diversity did not change significantly over time, the Firmicutes-to-Bacteroidetes (F/B) ratio significantly decreased after 12 weeks of HLCD.
Metabolite Profiling and Fecal Biomarkers
The team also performed targeted metabolomics, measuring 217 metabolites in stool samples. No significant baseline differences were observed in metabolites between groups. However, by the end of the intervention, the HLCD and non-HLCD groups showed distinct profiles in fecal metabolites. The HLCD intervention significantly decreased fecal levels of amino acids, particularly branched-chain amino acids, indoles, and carbohydrates. The TRE group showed reduced levels of carbohydrates, fatty acids, and amino acids but exhibited higher levels of indole acetic acid and deoxycholic acid. Interestingly, at the 28-week post-intervention follow-up, most clinical parameters had reverted to baseline levels. However, the HLCD group maintained a reduced body fat percentage compared to baseline, and some gut microbial and fecal metabolite changes observed with HLCD persisted.
Conclusions and Implications
Overall, both TRE and HLCD demonstrated additional benefits in BMI reduction beyond CR, with HLCD resulting in more significant fat mass loss and TRE favoring lean mass retention. Both TRE and HLCD elicited meaningful changes in the gut microbiome and metabolite profiles. While many improvements from the interventions were not sustained at 28 weeks post-intervention, the HLCD group continued to exhibit reduced fat mass. The results suggest that incorporating nutrient quality into low-carb diets and structured eating windows may provide sustainable metabolic benefits for individuals with obesity.