Dietary Carbohydrate Manipulation and Energy Balance: RCT

This study will investigate how dietary sugar and carbohydrates influence metabolism and health across a 12-week period, with a focus on physical activity. One third of participants will eat a diet with typical amounts of sugar and carbohydrate, one third of participants will eat a diet with sugar intake restricted, and the final third of participants will eat a diet where both sugar and total carbohydrates are restricted and replaced with fat.

Sugar is perceived negatively, leading to government taxation and targets to reduce consumption. These actions have been taken based on the limited evidence that high-sugar diets are associated with greater total energy intake. However, energy intake is only one half of the energy balance equation (energy in vs energy out). Without considering energy expenditure, it is impossible to fully understand the effects of sugar on health. Removing dietary sugar or carbohydrates from the diet may influence energy balance through mechanisms other than energy intake - for example by reducing levels of physical activity.

Understanding dietary regulators of energy balance is more important than ever because diseases like obesity are a consequence of energy surplus (i.e. energy in \> energy out). No studies have investigated a causal role of dietary sugar or carbohydrate on energy balance. The proposed research will seek to understand the responses to manipulating dietary carbohydrate and sugar content on energy balance and health. This research will enable the public to make informed dietary choices about carbohydrate and sugar consumption.

To achieve this, healthy non-obese adults, aged 18-65 years will be recruited to take part in an intervention study with measures of energy intake, energy expenditure, metabolic health, gut microbiota, and appetite. All laboratory trials will take place at the University of Bath. Participants will be randomised to consume one of three diets for a period of 12 weeks, with laboratory visits at baseline, at week 4, and at week 12:

1. CONTROL (moderate sugar) - reflecting the composition of a typical European diet
2. Low sugar - the same composition of a typical European diet but with \<5% energy intake from sugar
3. Low carbohydrate - low carbohydrate diet with \<5% energy intake from sugar, replacing carbohydrate energy with fat

Eligibility Criteria:
Inclusion Criteria:

* Body mass index 18.5-29.9 kg∙m-2
* Age 18-65 years
* Able and willing to provide informed consent and safely comply with study procedures
* Females to maintain record of regular menstrual cycle phase/contraceptive use
* No anticipated changes in physical activity during the first 4 weeks of the study (e.g. holidays or training programmes)

Exclusion Criteria:

* Any reported condition or behaviour deemed either to pose undue personal risk to the participant or introduce bias
* Any diagnosed metabolic disease (e.g. type 1 or type 2 diabetes)
* Any reported use of substances which may pose undue personal risk to the participants or introduce bias into the experiment
* Lifestyle not conforming to standard sleep-wake cycle (e.g. shift worker)
* Any reported recent (\<6 months) change in body mass (± 3%)
* Use of antibiotic medication in the last 3 months
* Use of prebiotic or probiotic products in the last month