Evaluating the Metabolic Effects of Dietary Nitrate Supplementation

Dietary nitrate is found to enhance muscle fatty acid oxidation/glucose uptake and increase mitochondrial biogenesis, which in turn, aid in the prevention and management of metabolic diseases. In recent years, inorganic nitrate supplementation is clinically emerging as a therapeutic strategy for possible treatment and management of metabolic diseases and cardiometabolic disorders. This is mostly explored in healthy/obese subjects, for improving blood pressure, endothelial function, insulin response and vascular effects. However, the metabolic effects of dietary nitrate for improving skeletal muscle glucose/lipid metabolism, muscle mitochondrial metabolism, muscle blood flow and body fat composition are not comprehensively studied in diabetic/pre-diabetic subjects. Hence, this study aims to evaluate the therapeutic efficacy of a natural nitrate supplement (beetroot juice) for improving overall metabolic health in obese pre-diabetic and non-diabetic subjects.

Skeletal muscle plays a key role in glucose and energy homeostasis and is involved in metabolizing a substantial proportion of glucose through glucose oxidation as well as through non-oxidative pathways. Skeletal muscle insulin resistance is one of the key driving factors associated with the pathophysiology of type 2 diabetes (T2D) and muscle dysfunction. Further, mitochondrial dysfunction is implicated in the pathogenesis of insulin resistance, insulin secretion and T2D. Enhancement of muscle fatty acid oxidation/glucose uptake along with increased mitochondrial biogenesis using natural supplements is an emerging strategy for preventing and managing metabolic diseases. One such natural supplements is nitrate (NO3). The oral microbiome plays a prominent role in the bioactivation of dietary nitrate (NO3) to nitrite (NO2), which is further reduced to nitric oxide (NO) in the gastrointestinal tract to maintain NO homeostasis and vascular health. NO is an important physiological signaling molecule and is involved in the modulation of skeletal muscle functions including regulation of blood flow (hemodynamic effect), muscle contractility, glucose, calcium homeostasis, mitochondrial respiration and biogenesis.

The use of dietary NO3 supplementation has been explored in the literature for mainly improving blood pressure, endothelial function, insulin response, and vascular effects in healthy/obese subjects. However, the metabolic effects of dietary NO3 for improving skeletal muscle glucose/lipid metabolism, muscle mitochondrial energetics, muscle blood flow, and body fat composition are not well studied in diabetic/pre-diabetic subjects.

In view of the potential health benefits of NO3/NO, this study plans to evaluate the therapeutic efficacy of a natural supplement, beetroot juice (rich in NO3) for improving the skeletal muscle mitochondrial function, muscle energetics, insulin sensitivity/glucose homeostasis, body fat composition and overall metabolism in middle aged (40 - 65 years) healthy and pre-diabetic male subjects. This would be the very first pilot study in the domain of metabolic diseases to evaluate the overall metabolic health of both obese pre-diabetic and non-diabetic male subjects using an advanced and comprehensive multi-model metabolic imaging approach.

Eligibility Criteria:
Inclusion Criteria:

1. Males aged 40 - 65 years old, residing in Singapore
2. Body mass index (BMI) 23 - 30 kg/m2
3. Glucose metabolism: a. Normal group with having FPG \< 5.6 mmol/L and HbA1c \< 5.7, b. Pre-diabetes group FPG 5.6 to 6.9 mmol/L, and HbA1c \< 6.5 %.
4. Willing to refrain from using oral mouth wash during study participation
5. Willing to adhere to study protocol

Exclusion Criteria:

1. Any current diagnosis or history of cardiovascular, hepatic, renal, metabolic (e.g. diabetes), gastrointestinal diseases, psychiatric disorders or diseases having impact on the study
2. Suffering from current oral health conditions such as gum diseases, oral cancer or mouth injury
3. Having medication and/or supplements which are known to influence glucose and insulin and muscle mitochondrial metabolism (e.g. Vitamin A, B, C and D, peroral corticosteroids)
4. Having medication for oral health conditions in the last 4 weeks and/or using oral mouth wash (e.g Listerine) in the last 2 weeks
5. Uncontrolled hypertension (blood pressure \> 160/100 mmHg)
6. Current smoker or excessive alcohol intake (\>4 standard drinks per day)
7. Known allergy/intolerance to beetroot family (eg: beetroot, spinach)
8. Undergoing weight loss diet and/or programs
9. Having contraindications for MRI e.g. metallic implants such as cardiac pacemaker
10. Receiving antibiotics or suffering from diarrhoea in the last 4 weeks
11. Consuming supplement(s) which contains nitrate