Scot Sweet Study (Interaction of a Non-nutritive Sweetener With a High-fibre Weight Loss Diet)

• Phase 1 Control (Other), also known as CTRL: Control diet (30% Fat, 15% Protein, 55% Carbohydrate, Fibre rising from 10 to 16g/d). Fed to energy balance (1.5 x Resting Metabolic Rate, RMR).
• Phase 2 High Fibre Weight Loss (Other), also known as HF WL: High Fibre Weight Loss diet (30% Fat, 15% Protein, 55% Carbohydrate). Fed to energy deficit (100% RMR). The quantity of fructo-oligosaccharides (FOS) will be fixed at 20g/day for all kcal levels with additional fibre coming from the diet provided. The FOS will be split over breakfast, lunch and dinner in drinks/yoghurts which will be compulsory to consume.
• Phase 3 High Fibre and Non-Nutritive Sweetener Weight Loss (Other), also known as HF-NNS WL: High Fibre and Non-Nutritive Sweetener Weight Loss diet (30% Fat, 15% Protein, 55% Carbohydrate). Fed to energy deficit (100% RMR). The quantity of fructo-oligosaccharides (FOS) and non-nutritive sweetener (sucralose) will be fixed at 20g/day and 30mg/day respectively for all kcal levels with additional fibre coming from the diet provided. The FOS and sucralose will be split over breakfast, lunch and dinner in drinks/yoghurts which will be compulsory to consume.

Primary outcomes

• Change in gut metabolites (from faecal samples) in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: Measured by changes in faecal short chain fatty acids concentrations
• Change in gut microbiome composition (from faecal samples) in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: Measured by changes in bacterial 16S ribosomal ribonucleic acid gene sequencing; 16S rRNA
• Change in gut metabolite production (from faecal samples) in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: Measured by changes in calprotectin concentrations

Secondary outcomes

• Change in free-living glycaemic control in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured using continuous glucose monitoring (CGM)
• Change in glycaemic control in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: measured by changes in fasted plasma glucose and insulin

Other outcomes

• Change in concentration of blood metabolites in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: measured by changes in fasted plasma short chain fatty acid (SCFA) concentrations
• Change in concentration of gut hormones in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: measured by changes in fasted plasma ghrelin, GLP-1 and peptide YY (PYY) concentrations
• Change in lipid profile in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: measured by changes in fasted plasma lipid profile (Total cholesterol, HDL-cholesterol, LDL-cholesterol, triglycerides and non-esterified fatty acids (NEFA)
• Change in lipid ratios in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: Total cholesterol, HDL-cholesterol and LDL-cholesterol measures will be combined to report TC to HDL and LDL to HDL ratios.
• Change in concentration of urinary metabolites in response to dietary fibre and non-nutritive sweetener [At baseline and end of each arm (study days 1, 15, 29 and 43)]: changes in urinary metabolite concentrations measured by metabolomics
• Height [At screening visit only]: measured in metres
• Change in body weight in response to dietary fibre and non-nutritive sweetener [At screening and 3 times a week on each arm (20 occasions from date of screening up to study day 43)]: measured as weight in kilograms
• Change in Body Mass Index (BMI) in response to dietary fibre and non-nutritive sweetener [At screening and 3 times a week on each arm (20 occasions from date of screening up to study day 43)]: weight and height measures will be combined to report BMI in kg/m\^2
• Change in daily nausea symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced nausea today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily bloating symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced bloating today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily flatulence symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced flatulence today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily abdominal cramp symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced abdominal cramps today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily intestinal rumble symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced rumbles today? (intestinal sounds)', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily diarrhoea symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced diarrhoea today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily constipation symptoms in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a Likert scale 'Have you experienced constipation today?', scored as 0 - no more symptoms than usual, 1 - slightly more symptoms than usual, 2 - noticeably more symptoms than usual, 3 - considerably more symptoms than usual.
• Change in daily bowel movements in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a scale 'How many bowel movements have you had today?', scored as 0, 1, 2, 3 or >3.
• Change in daily hunger rating in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a visual analogue scale 'How hungry have you felt today?', scored from 0 (Generally not at all hungry) to 100 (Generally as hungry as I've ever felt).
• Change in daily fullness rating in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a visual analogue scale 'How full have you felt today?', scored from 0 (Generally not at all full) to 100 (Generally as full as I've ever felt).
• Change in daily desire to eat rating in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a visual analogue scale 'How strong has your desire to eat been today?', scored from 0 (Very weak) to 100 (Very strong).
• Change in retrospective food consumption rating in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: measured daily, at end of day, using questionnaires. Question presented as a visual analogue scale 'How much do you feel you could have eaten today?', scored from 0 (Nothing at all) to 100 (A large amount).
• Change in appetite in response to dietary fibre and non-nutritive sweetener [every day of study diets (42days)]: Mean of hunger, fullness, desire to eat and retrospective consumption ratings will be combined to report an overall appetite score (from 0 to 100)
• Change in food intake [at screening (7days) and every day of study diets (42days)]: measured using weighed intake records

Sex: All, ages: 18 Years to any, accepts healthy volunteers

Inclusion Criteria:

* healthy but overweight/obese (BMI 28-40kg/m2) males and females (postmenopausal, using the oral contraceptive pill or some form of hormonal contraceptive)
* moderate habitual fibre intake (18-23g/day)

Exclusion Criteria:

Medication exclusion criteria:

* antibiotic use (within the past 3 months due to impact on gut microbiota)
* anti-depressants (current)
* smoking or vaping
* weight loss medication

Medical exclusion criteria:

* Females who are planning to be pregnant, are pregnant or are breastfeeding
* Anyone with food allergies, self-reported food sensitivity or intolerance
* Anyone with coeliac disease or gluten intolerance
* Anyone taking medication which may affect their appetite
* Anyone with an eating disorder
* Anyone with diabetes
* Anyone with a gastrointestinal disorder, kidney disease, liver disease or gout
* Anyone suffering from a psychiatric disorder or any type of substance abuse
* Anyone suffering from unregulated thyroid disease

Other exclusion criteria:

* Anyone following a vegetarian or vegan diet
* Anyone following a current weight loss programme (that may be affecting lifestyle, physical activity \& diet) or undergone gastric band/reduction surgery
* Anyone with unsuitable veins for blood sampling
* Anyone who is unable to fluently speak, read and understand English
* Anyone who is unable to comply to an alcohol-free diet for 6 weeks

Current sweetener consumption will not be an exclusion criteria as the Phase 1 - CTRL and Phase 2 - HF WL diets will provide enough of a washout (4 weeks) before the Phase 3 diets containing sucralose are consumed. Participants who do habitually consume sweeteners will be asked not to use them during the study.

• Alexandra Johnstone, Prof, Principal investigator, Rowett Institute, University of Aberdeen
• Alexander Ross, Dr, Principal investigator, Rowett Institute, University of Aberdeen