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

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.

Inclusion criteria

• Participant is able to give written informed consent for their participation in the study.
• Healthy.
• Non-smoking adults.
• Male or female.
• Aged 60 to 75 years.
• BMI between 25 and 40 kg/m2.

Exclusion criteria

• Systolic BP > 180mmHg and/or diastolic BP >110mmHg at the Clinic Screening Visit.
• Contraindication for MRI.
• Does not have adequate understanding of verbal and written information in English, sufficient to complete an MRI safety screening and to give informed consent.
• Any existing or previous medical condition that may affect the study outcomes (i.e., diabetes, kidney dysfunction, malignant cancer, brain surgery, stroke).
• Any medical treatment that may affect the study outcomes (i.e., diuretics, anti-acids, organic nitrates, anti-pyschotics or neuro-stimulants).
• Evidence of an eating disorder as indicated by the Three-factor eating questionnaire (Eating Attitudes Tests-26).
• Blood donation within the last 3 months of the anticipated intervention beginnings.
• Having taken part in a research study in the last 3 months involving invasive procedures or an inconvenience allowance.
• High-alcohol consumers (≥ 14 units/week for females, and ≥ 22 units/week for males).
• Vegetarianism (likely to have very high nitrate intake and food provided during the dietary intervention unsuitable).
• Weight change over 3.0kg in the last 2 months (important influence on vascular function).