• Change in body weight [ Time Frame: Week 0, visit week 6 and week 12 ]
  body weight will be measured on visit week 0, visit week 6 and visit week 12
• Change in dietary intake [ Time Frame: Week 0, visit week 6 and week 12 ]
  participants will fill out 3 days of diet recalls before coming to all 3 study visits using Intake24
• Change in waist circumference [ Time Frame: Week 0, visit week 6 and week 12 ]
  waist circumference will be measured on visit week 0, visit week 6 and visit week 12
• Change in appetite [ Time Frame: Week 0 and week 12 ]
  Appetite questionnaires (three factor eating questionnaire, sweet food frequency questionnaire, Satiety, hunger, and food cravings - using the Control of Eating Questionnaire ) will be completed on visit week 0 and visit week 12
• Change in fasting blood glucose [ Time Frame: Week 0 and week 12 ]
  Fasting blood glucose will be measured on visit week 0 and visit week 12.
• Change in the 75-OGTT 2-hour blood glucose [ Time Frame: Week 0 and week 12 ]
  75g OGTT 2-h blood glucose will be measured on visit week 0 and visit week 12.

• Physical activity [ Time Frame: Week 0, visit week 6 and week 12 ]
  Total MET-minutes per week measured via the International Physical Activity Questionnaire (IPAQ).
• Physical activity [ Time Frame: Week 0, week 6, week 12 ]
  Number of steps per day. 3 days before visit week 0, visit week 6 and visit week 12
• Blood pressure [ Time Frame: Week 0, visit week 6 and week 12 ]
  Blood pressure will be measure on visit week 0, visit week 6 and visit week 12
• Composition of gut microbiome [ Time Frame: Week 0 and week 12 ]
  Changes in gut microbiota will be measured by 16S rRNA gene sequencing. This outcome is optional and will be decided by the investigators based on the findings in the primary outcome.
• Fasting plasma insulin [ Time Frame: Week 0 and week 12 ]
  This outcome is optional and will be decided by the investigators based on the findings in the primary outcome
• 75g OGTT derived iAUC plasma insulin [ Time Frame: Week 0 and week 12 ]
  This outcome is optional and will be decided by the investigators based on the findings in the primary outcome.

• Physical activity [ Time Frame: Week 0, visit week 6 and week 12 ]
  monitoring with IPAQ, and pedometer app downloaded in participants smartphones
• Blood pressure [ Time Frame: Week 0, visit week 6 and week 12 ]
  Blood pressure will be measure on visit week 0, visit week 6 and visit week 12
• Composition of gut microbiome [ Time Frame: Week 0 and week 12 ]
  Changes in gut microbiota will be measured by 16S rRNA gene sequencing. This outcome is optional and will be decided by the investigators based on the findings in the primary outcome.
• Fasting plasma insulin [ Time Frame: Week 0 and week 12 ]
  This outcome is optional and will be decided by the investigators based on the findings in the primary outcome
• 75g OGTT derived iAUC plasma insulin [ Time Frame: Week 0 and week 12 ]
  This outcome is optional and will be decided by the investigators based on the findings in the primary outcome.

Excess consumption of caloric sweeteners contributes to the alarming rates of overweight and obesity, whereas non-nutritive sweeteners (NNS) are non-caloric alternatives offering sensory and health benefits. NNS are widely used to moderate energy intake and postprandial glycaemia, but there is controversial evidence about their role and effects. Stevia, a natural NNS, has been suggested to assist with glucose regulation but data on glucose tolerance after daily consumption of stevia are lacking. The investigators plan to undertake a pilot randomized 2-parallel arm open-label 12-week trial, where participants will start consuming stevia with their habitual drinks. Thirty healthy volunteers (not habitual consumers of stevia or other NNS) will be recruited. The intervention group (n=15) will consume 5 drops of stevia with their habitual drinks twice daily whereas the control group (n=15) will not be required to change anything in their diet, but avoid consuming NNS or diet beverages for the study duration.

Key measures in glucose homeostasis including glucose response to an oral glucose tolerance test will be performed before and after the intervention period. Serum and plasma samples will be stored for potential analysis of insulin and gut hormones levels.

Participants will have to attend 3 study visits, visit week 0, visit week 6 and visit week 12, but the primary outcome will be assessed in visit week 0 and visit week 12.

Participants will be weighed; dietary intake, physical activity and appetite will be also assessed. Faecal samples will be collected and gut microbiome analysis may be performed. Gut microbiome has been considered to be a key linked topic, since it has been suggested that saccharin consumption may induce glucose intolerance in humans through alterations in gut microbiota in humans.

The trial will assess whether regular use of stevia in realistic amounts has any effects on glucose homeostasis, and aims to elucidate our understanding of long-term physiological effects of NNS.

• Glucose Intolerance
• Obesity

• Experimental: Stevia arm
  stevia drops
  Intervention: Dietary Supplement: stevia
• No Intervention: Control arm
  No change in diet

Inclusion Criteria:

• Age 18-40 years
• BMI 18.5-25 kg/m2
• No or low NNS consumers (up to 1 can of diet soda per week or 1 sachet of NNS per week)
• DEBQ for restraint eating ≤ 3
• Healthy - general good health
• Not taking medications that affect metabolism or appetite (i.e. thiazide diuretics, glucocorticoids or beta blockers)
• Stable weight, ≤ 5 kg last 12 months
• Fasting blood glucose ≤6.0 mmol/L
• Willing to comply with the study protocol
• No self-reported food allergy or intolerance to foods supplied during the study
• The participant is capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form.
• The participant is able to read, comprehend and record information written in English.
• A signed and dated written informed consent is obtained from the participant.

Exclusion Criteria:

• Age under 18 years or over 40 years old.
• BMI >25 kg/m2 and <18.5kg/m2
• Participants who are not willing to comply with study procedures (including expression of dislike for NNS)
• Habitual NNS consumers, >1 can of diet beverage or >1 sachet of low calorie sweeteners per week.
• Fasting blood glucose measured > 6 mmol/L
• Subjects who are currently dieting and having ceased a diet in < 4 weeks
• DEBQ score for restraint eating > 3
• Subjects who follow special diets for weight maintenance, such as Atkins Diet, Weight Watchers, gluten-free diet, The Zone diet, Vegetarian Diet, Raw Food Diet etc.
• Vegetarians, vegans
• Subjects who take recreational substances such as cannabis.
• Presence of any chronic condition requiring medication that might affect our results (e.g. diabetes, mental diseases, gastrointestinal diseases)
• Subjects with eating disorders (binge eating disorder, bulimia etc)
• Subjects who are currently experiencing anxiety or depression
• Participants who drink alcohol more than the NHS guidelines (14 units per week)
• >10 h of vigorous physical activities per week and/or planning to increase/decrease physical activity levels in the next months.
• Having ceased smoking in the last six months
• Female participants who are, or may be, pregnant, or currently lactating.
• Subjects who regularly consume dietary supplements for weight loss, muscle building etc.
• Subjects with food allergies or intolerances related to the study.
• Subjects who have given blood elsewhere within the last month.
• The participant cannot read, comprehend and record information written in English.