Background:
Weight loss and subsequent maintenance improves cardio-metabolic health in individuals with obesity. Very-low-calorie diets (VLCD), typically high in animal protein, are effective for weight loss, but difficult to maintain [1, 2]. There is increasing interest in alternative dietary protein sources, but it is unclear if they offer comparable efficacy regarding weight loss [3]. Mycoprotein is a fungal-derived non-animal protein source, rich in fibre that has been reported to promote satiety and improve cardiometabolic risk factors relative to animal proteins [4, 5]. This suggests utility of mycoprotein as a promising alternative dietary protein source for diets designed for weight management.

Aim:

This study evaluates whether a mycoprotein-rich VLCD (MYC) induces and maintains clinically meaningful weight loss in adults with obesity compared with a conventional omnivorous VLCD (OMN).

Methods:
Adults with obesity (BMI≥30 kg·m⁻²) were stratified by age, sex, and BMI before randomisation to OMN (n=5) or MYC (n=5) diets, or a non-intervention control (n=2) group (CON). Phase 1 of the intervention comprised a six-week VLCD phase, with energy intake prescribed at 800 kcal.day^-1 and protein derived from the specified source providing 85 g·day⁻¹, corresponding to 42.8 ± 1.1 %En^.day. Phase 2 involved a six-week controlled weight-maintenance phase, with 70% estimated energy requirements prescribed, and the remaining 30% self-selected. Body mass and composition, resting energy expenditure and cardiometabolic health markers were assessed weekly. Data were analysed using repeated-measures ANOVA with group and time as factors, with statistical significance set at P<0.05.

Results:

During Phase 1, body mass remained unchanged in CON (from 111.0±5.4 to 112.2±5.3 kg) but decreased (P<0.001) to a similar degree in OMN (−10.0±1.1 kg; −10.0±1.3%) and MYC (−9.9±1.2 kg; −9.7±0.6%), respectively. During Phase 2, body mass remained stable in CON (from 112.2±5.3 to 112.6±5.1 kg) but continued to decrease (P<0.001) in OMN (−4.1±1.1 kg; −4.8±1.4%) and MYC (−4.6±1.4 kg; −5.0±1.5%), respectively, with no differences between intervention groups. In Phase 1, body fat mass remained unchanged in CON (53.9±2.8 to 55.1±3.1 kg) but decreased significantly (P<0.001) in both intervention groups, decreasing in OMN (−7.6±1.0 kg; −16.9±1.9%) and MYC (−7.6±1.0 kg; −15.6±2.0%), with no differences between intervention groups. During Phase 2, body fat mass remained unchanged in CON (55.1±3.1 to 56.3±1.3 kg) but decreased (P<0.001) in both OMN (-3.5±0.9 kg; -8.1±2.2%) and MYC (-5.7±0.9 kg; -13.8±2.3%) intervention groups to a similar extent. During Phase 1, skeletal muscle mass remained unchanged in CON (from 27.3±1.3 to 26.9±1.5 kg) but decreased (P=0.005) in both intervention groups to a similar extent; in OMN by −0.88±0.3 kg (−3.8±1.30%) and in MYC by −1.42±0.30 kg (−5.8±1.2%). Skeletal muscle mass did not change during phase 2 in any of the groups. Further participants and outcomes will be completed and presented by the time of the meeting.

Conclusion:
Thus far, both OMN and MYC high protein VLCDs have been equivalently effective at inducing large reductions in body mass and body fat. The findings so far indicate the utility of mycoprotein as an alternative dietary strategy to achieve short- and medium- term weight management which may suit weight loss goals of individuals with different dietary preferences.