The Combined Effect of Dietary Nitrate and Caloric Restriction on Cognitive and Vascular Function.

This pilot study will compare the effect of combining dietary nitrate and caloric restriction versus dietary nitrate alone. The participant will be contacted, having responded to an advertisement on social media and posters, to attend the screening visit. They will be asked about their health status, suitability for MRI and availability. The investigators will use physical activity and eating attitude questionnaires. The investigators will also measure their height, weight, body mass index (BMI), and blood pressure (BP) and undertake blood tests. If they are eligible, they will be randomised to one of the two arms. The first group will consume nitrate-rich beetroot juice with a calorie-restricted diet for 28 days. The second group will drink the same juice with a weight-maintenance diet for the same period. The food and drinks will be provided. The outcome measures will be measured twice (at the baseline and end visits) to evaluate the change. The primary outcome is the cognitive function. The secondary outcomes are peripheral vascular health (BP and microvascular perfusion), cerebral vascular health (brain blood flow), anthropometry, body composition, and exhaled NO and nitrate concentrations. Also, the feasibility and accessibility of the study will be assessed.

Twenty healthy males and females, aged 60-70 years, non-smokers, and living with overweight or obesity (BMI 25-40 kg/m2) will be recruited to a 28-day pilot, randomised, parallel trial to follow one of the interventions (dietary nitrate with calorie-restricted diet or dietary nitrate with weight-maintenance diet) if they are eligible. Their energy requirement will be calculated using the Mifflin-St Jeor Equation, and the participant will be instructed to follow a healthy diet ( pre-diet standardisation) for three days before the intervention to minimise the effect of the sudden change of their habitual diet (during which their energy requirement will be met). At the Baseline Visit (Day 0), they will be randomised to one of the two arms, and the outcome measurements will be taken. Cognitive function will be measured via a pen-and-paper test (TMT) and a cognitive battery of tests (COMPASS). Clinic and home resting blood pressure (BP) will be measured using an automated BP monitor. Microvascular perfusion will be measured by a Laser Doppler monitor. Cerebral blood flow will be measured using a brain MRI scan. Height, weight, BMI, skinfold thickness, and waist circumference will be measured via a wall-mounted stadiometer, calibrated scale, BMI equation, calipers, and a tape measure, respectively. Body composition will be measured by a bioelectrical impedance analysis (BIA). Exhaled NO will be measured using a fractional exhaled nitric oxide analyser (FeNO). Blood samples will be taken to measure plasma nitrate concentrations. Physical activity will be monitored through a wearable smartwatch with an integrated accelerometer. The participants will be provided with 14 bottles of nitrate-rich beetroot juice (70 ml, which provides 6.5mmol of nitrate/day) with their allocated diet to be consumed in the next 14 days, starting from the next day (Day 1), and the remaining 14 days' supply will be delivered on Day 13. There will be an energy deficit of 1,000 kcal/day if they are allocated to the caloric restriction group. Otherwise, the energy requirement will be met. After completing the 28-day intervention, the participant will attend the End Visit (Day 29), to repeat the same study measurements they have done in the Baseline Visit. An exit feedback questionnaire will be given to collect information on the acceptability and compliance with the measurement protocols and intervention.