Impact of Beta-glucan Supplementation During Calorie and Carbohydrate-restricted Diet on Body Weight and Body Fat Loss, Appetite, and Gastrointestinal Appetite Hormones.

This study will investigate whether beta-glucan supplementation, when added to an energy and carbohydrate-restricted diet, facilitates body weight and body fat loss, and leads to less detrimental changes in subjective appetite and gastrointestinal appetite hormones. This will be a double-blind, randomised, controlled trial in which healthy females living with overweight and obesity will be randomly assigned to a beta-glucan or a cellulose (placebo) group (1:1 basis).

Participants Based on power calculations and taking into consideration a drop-out rate of approximately 25%, this study will aim to recruit 60 sedentary females living with overweight or obesity (30 in each group), aged between 18 and 60 years and with a body mass index (BMI) between 25 and 39.9 kg/m².

Study design To confirm the eligibility, study participants will undergo a screening session. The screening visit will involve completion of a health questionnaire, height and body weight, and resting metabolic rate measurements. Eligible participants will be randomised either to the beta-glucan or the placebo group. Randomisation will be performed using Excel software. To ensure that the study was blinded, an independent person labelled the packs of fibre as either 'A' or 'B', indicating the β-glucan or placebo group.

Prior to the 4-week intervention, participants will undergo an experimental trial. This trial will be conducted at the Metabolic Investigation Laboratory, beginning at approximately 9:00 am, following an overnight fast. Height and body weight will be measured using the same procedures employed during the screening session. Participants will then complete a subjective appetite questionnaire. After that, a cannula will be placed into the antecubital vein. After a 10-minute rest period, a fasting blood sample will be collected. Following this, a baseline saliva sample will be obtained, and participants will be asked to consume deuterium oxide (D₂O) mixed with regular drinking water. Immediately after the baseline saliva collection, participants will consumed a standardised low-calorie breakfast (~200 kcal; carbohydrates: 20-25 g, protein: 15-20 g, fat: ~3 g, fibre: ~2 g) which will be a liquid meal replacement (Cambridge Weight Plan, Corby, UK), mixed with either 3 g of β-glucan or 3 g of cellulose as a placebo. During the experimental trials, blood samples and subjective appetite scores will be collected at 30-minute intervals for the duration of 240 minutes, and additional saliva samples will be collected at 3 hours and 3.5 hours post-ingestion of deuterium oxide water. The identical trial will be conducted after the intervention completion.

During the 4-week intervention, participants will consume an energy and carbohydrate-restricted diet combined with 9 g/day of beta-glucan (beta-glucan group) or 9 g/day of cellulose (Placebo group). During the 4-week intervention, breakfasts and dinners will consist of energy-restricted meal replacements providing 200 kcal/ meal, while lunches will be low-carbohydrate meals providing 35% of habitual energy intake.

During the intervention, participants will be provided with the supplements (beta-glucan or placebo) and low-energy liquid meal replacement sachets in two separate batches. This approach is expected to support compliance with the study products. Participants were instructed to consume 9 g/day either a beta-glucan or a placebo supplement with each main meal (breakfast, lunch, and dinner). For breakfast and dinner, the fibre will be mixed with the provided meal replacements. For lunch, participants will be advised to mix supplements with yoghurt, juice, or water based on personal preference. Participants will be contacted by telephone or email once a week to provide dietary review and support. Participants will be encouraged to avoid consuming alcohol or to have a maximum of two units per week.

Outcome Measures Fat-free mass (FFM) and fat mass (FM) will be measured in both pre-intervention and post-intervention experimental trials using a stable isotope dilution method with deuterium oxide (D₂O) as a tracer. The amount of D₂O in the body will be analysed using Fourier Transform Infrared Spectrometry.

This technique has been used for the last 50 years to estimate total body water (TBW), which is used to calculate fat-free mass and teh fat mass.

Subjective appetite scores will be measured using the Visual Analogue Scale (VAS). The scale is 100 mm in length with words anchored to a minimum and a maximum of the ''desire to eat'', ''fullness'', ''hunger'', ''capacity to eat'' and ''satiety'' the point corresponding to their sensations. The response will be calculated by measuring the distance in millimeters from the left-hand anchor to the participant's mark. All scores will be completed manually.

Appetite-Related Hormones. The measurements of plasma concentration of total ghrelin, acylated ghrelin, PYY, GLP-1 will be measured using ELISA kits (Merck, Millipore, Bioscience Division, UK).

Dietary assessment. Food diaries and electronic kitchen scales (Salter Housewares Ltd., Tonbridge, UK) will be given to participants on the screening day, and participants will be instructed on how to use the scales to record 3-day food and beverage intake. Dietary records will be analysed for energy and macronutrient intake using the Nutritics dietary analysis software (Dublin, Ireland). The dietary assessment data were used to characterise participants' habitual dietary patterns.

Statistical Analysis. Mixed ANOVA using the general linear model with group (control and β-glucan) will be used for assessing the effect of time, group, and time*group interaction on body weight, fat mass, fat-free mass, composite appetite scores, and gastrointestinal appetite hormones (total ghrelin, PYY and GLP-1).