Increase in colonic propionate as a method of preventing weight gain in adults aged 20–40 years: iPREVENT, a multicentre, double-blind, randomised, parallel-group trial

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Background Overweight and obesity affect over 60% of the United Kingdom population and constitute a major risk factor for the development of comorbidities. Preventing weight gain in periods of life where there is an elevated risk of adipose tissue expansion could be beneficial in preventing associated diseases in later life. This study investigated the impact of inulin-propionate ester on the prevention of weight gain in young people who were at risk of gaining weight. Objectives To investigate the impact of increasing colonic production of the short-chain fatty acid propionate on preventing body weight gain, in younger adults, over 12 months. Several underpinning mechanisms were investigated in a substudy. Design iPREVENT was a randomised, parallel-group, placebo-controlled, double-blind trial, designed with 90% power to detect a 2 kg between-arm difference in weight gain at 12 months. Setting This trial was performed at the Imperial Clinical Research Facility in London and the University of Glasgow Clinical Research Facility. Participants Participants were 20–40 years old, with a body mass index of 24.0–27.0 kg/m2 if of South Asian ethnicity or 25.0–30.0 kg/m2 if non-South Asian. Participants were also required to have at least one of the following risk factors: weight gain in the past year, low physical activity, low intake of fruit and vegetables or high intake of sugar-sweetened beverages. A total of 270 participants (135 per arm) were randomised. Intervention Participants were randomised to either 10 g/day inulin-propionate ester or 10 g/day inulin control (fermentable oligosaccharide) consumed daily for 12 months. Main outcome measure The primary outcome was weight gain from baseline to 12 months. Results The mean (± standard deviation) body weight at baseline for inulin was 79.1 kg ± 10.6 (n = 135) and inulin-propionate ester 79.6 kg ± 10.9 (n = 135). At 12 months body weight was 78.9 kg ± 11.8 (n = 114) and 81.4 kg ± 11.9 (n = 112) for inulin and inulin-propionate ester, respectively. The baseline-adjusted mean difference in weight gain was 1.02 (95% confidence intervals −0.37 to 2.41) kg for inulin-propionate ester versus inulin control. Of the secondary outcomes, the confidence interval cautiously supports differences in fat-free mass; 1.07 kg (0.21 to 1.93) (N = 226), body water; 0.72 kg (0.1 to 1.33) (N = 226) and fasting glucose; 0.11 mmol/l (0.01 to 0.21) (N = 191). Compliance with inulin-propionate ester treatment of ≥ 50% over 12 months was 63% (n = 135). There were no unexpected adverse or serious adverse events. Limitations This study aimed to explore the efficacy of enhanced propionate production above background fermentation. It could be argued a negative control (a non-fermentable substrate e.g. cellulose) would have been more suitable. Metabolomic analysis of compliance could only be conducted on a subsection of the study population. There was no intention to conduct follow-up assessments on participants beyond their 12-month visit. Conclusions In adults below the age of 40 years, inulin-propionate ester did not affect weight gain compared with the control. Future work Previously we observed that inulin-propionate ester prevented weight gain in older adults, but not in this younger cohort. We aim to investigate the variation in responses between these age groups. Trial registration This trial is registered as ISRCTN16299902. Funding This award was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme (NIHR award ref: 15/185/16) and is published in full in Efficacy and Mechanism Evaluation; Vol. 12, No. 8. See the NIHR Funding and Awards website for further award information.

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