Dietary nitrate supplementation has shown promising ergogenic effects on endurance exercise. However, at present there is no systematic analysis evaluating the effects of acute or chronic nitrate supplementation on performance measures during high-intensity interval training (HIIT) and sprint interval training (SIT). The main aim of this systematic review and meta-analysis was to evaluate the evidence for supplementation of dietary beetroot-a common source of nitrate-to improve peak and mean power output during HIIT and SIT. A systematic literature search was carried out following PRISMA guidelines and the PICOS framework within the following databases: PubMed, ProQuest, ScienceDirect, and SPORTDiscus. Search terms used were: ((nitrate OR nitrite OR beetroot) AND (HIIT or high intensity or sprint interval or SIT) AND (performance)). A total of 17 studies were included and reviewed independently. Seven studies applied an acute supplementation strategy and ten studies applied chronic supplementation. The standardised mean difference for mean power output showed an overall trivial, non-significant effect in favour of placebo (Hedges' g = -0.05, 95% CI -0.32 to 0.21, Z = 0.39, p = 0.69). The standardised mean difference for peak power output showed a trivial, non-significant effect in favour of the beetroot juice intervention (Hedges' g = 0.08, 95% CI -0.14 to 0.30, Z = 0.72, p = 0.47). The present meta-analysis showed trivial statistical heterogeneity in power output, but the variation in the exercise protocols, nitrate dosage, type of beetroot products, supplementation strategy, and duration among studies restricted a firm conclusion of the effect of beetroot supplementation on HIIT performance. Our findings suggest that beetroot supplementation offers no significant improvement to peak or mean power output during HIIT or SIT. Future research could further examine the ergogenic potential by optimising the beetroot supplementation strategy in terms of dosage, timing, and type of beetroot product. The potential combined effect of other ingredients in the beetroot products should not be undermined. Finally, a chronic supplementation protocol with a higher beetroot dosage (>12.9 mmol/day for 6 days) is recommended for future HIIT and SIT study.

Aging is associated with a significant decline in neuromuscular function, leading to a reduction in muscle mass and strength. The aim of the present report was to evaluate the effect of supplementation with nitric oxide precursors (l-arginine and beetroot extract) in muscular function during a training period of 6 weeks in elderly men and women. The study (double-blind, placebo-controlled) involved 66 subjects randomly divided into three groups: placebo, arginine-supplemented and beetroot extract-supplemented. At the end of this period, no changes in anthropometric parameters were observed. Regarding other circulating parameters, urea levels were significantly (p < 0.05) lower in women of the beetroot-supplemented group (31.6 ± 5.9 mg/dL) compared to placebo (41.3 ± 8.5 mg/dL) after 6 weeks of training. In addition, the circulating creatine kinase activity, as an index of muscle functionality, was significantly (p < 0.05) higher in women of the arginine- (214.1 ± 162.2 mIU/L) compared to the beetroot-supplemented group (84.4 ± 36.8 mIU/L) at the end of intervention. No significant effects were noticed with l-arginine or beetroot extract supplementation regarding strength, endurance and SPPB index. Only beetroot extract supplementation improved physical fitness significantly (p < 0.05) in the sprint exercise in men after 6 weeks (2.33 ± 0.59 s) compared to the baseline (2.72 ± 0.41 s). In conclusion, beetroot seems to be more efficient during short-term training while supplementing, preserving muscle functionality in women (decreased levels of circulating creatine kinase) and with modest effects in men.

Abstract: Nitrate ingestion improves exercise performance; however, it has also been linked to adverse health effects, except when consumed in the form of vegetables. The purpose of this study was to determine, in a double-blind crossover study, whether whole beetroot consumption, as a means for increasing nitrate intake, improves endurance exercise performance. Eleven recreationally fit men and women were studied in a double-blind placebo controlled crossover trial performed in 2010. Participants underwent two 5-km treadmill time trials in random sequence, once 75 minutes after consuming baked beetroot (200 g with ≥500 mg nitrate) and once 75 minutes after consuming cranberry relish as a eucaloric placebo. Based on paired t tests, mean running velocity during the 5-km run tended to be faster after beetroot consumption (12.3±2.7 vs 11.9±2.6 km/hour; P=0.06). During the last 1.1 miles (1.8 km) of the 5-km run, running velocity was 5% faster (12.7±3.0 vs 12.1±2.8 km/hour; P=0.02) in the beetroot trial, with no differences in velocity (P≥0.25) in the earlier portions of the 5-km run. No differences in exercise heart rate were observed between trials; however, at 1.8 km into the 5-km run, rating of perceived exertion was lower with beetroot (13.0±2.1 vs 13.7±1.9; P=0.04). Consumption of nitrate-rich, whole beetroot improves running performance in healthy adults. Because whole vegetables have been shown to have health benefits, whereas nitrates from other sources may have detrimental health effects, it would be prudent for individuals seeking performance benefits to obtain nitrates from whole vegetables, such as beetroot.

The consumption of red beetroot has been associated with a number of health benefits. Antidiabetic properties have been suggested in the literature, yet evidence from in vivo and in vitro studies is very limited(1). A recent study has indicated a moderate reduction of postprandial glucose and insulin response following neobetanin rich beetroot juice consumption(2). Reductions of both, glucose and insulin, are considered beneficial with regards to lowering the risk of type 2 diabetes(3). The aim of our study was to investigate the acute effects of beetroot juice consumption in combination with carbohydrates on the glycaemic response in humans. We recruited ten healthy volunteers (1 male and 9 females), aged 20-24 years and BMI ranging from 16.7-26.8, for a randomized crossover study. Following an overnight fast, participants were asked to consume 270 ml beetroot juice or a sugar-matched control drink alongside white bread to provide 50 g available carbohydrates in each setting. The sugar content in the juice was analysed using HPLC prior to study start (sucrose 79.9 %, glucose 10.9 %, fructose 9.4 %). Capillary blood was collected via finger prick in regular intervals following juice and bread consumption (0, 15, 30, 45, 60, 90, 120, 150, 180 min) and blood glucose levels determined using glucometer. Data were analysed using two-tailed paired t-test. The consumption of beetroot juice in comparison to the sugar matched control drink reduced blood glucose levels significantly after 15, 30, 90 and 180 min (Fig 1, p < 0.05), demonstrating a reduction in peak and early phase as well as a delay in glycaemic response. All individuals responded to beetroot juice with a reduced or delayed blood glucose, however, to a differing extent which was not related to body weight or BMI. (Figure Persented) The lower blood glucose peak as well as a delayed glucose appearance indicate potential beneficial effects of beetroot juice consumption on postprandial glucose response which may relate to different mechanisms such as the inhibition of digestive enzymes, reduced and/or delayed glucose uptake, mechanisms that may involve betalain pigments, polyphenols as well as nitrates found in beet.

Dietary nitrate is known to lower blood pressure. Beetroot is a rich source of nitrate and could therefore be an important dietary component in the management of hypertension and cardiovascular disease, however consumption is relatively low. We evaluated the effects of beetroot enriched bread ingestion on acute microvascular reactivity, arterial stiffness and blood pressure response in healthy men.

BACKGROUND:

Diets rich in inorganic nitrate are associated with lower blood pressure, an effect that may be mediated by an improvement of endothelial function (EF). Therefore, a systematic review and meta-analysis of randomised controlled trials (RCTs) were conducted to examine the effects of inorganic nitrate and beetroot supplementation on measures of EF.

METHODS:

MEDLINE, EMBASE and Scopus databases were searched from inception until November 2014. Specific inclusion criteria were as follows: (1) RCTs; (2) trials comparing inorganic nitrate or beetroot supplementation with placebo control groups; and (3) trials reporting effects of these interventions on outcomes of vascular function. Random-effect models were used to assess the pooled effect sizes showed as standardised mean differences (SMD).

RESULTS:

Nine crossover trials and three parallel trials met our inclusion criteria. The trials were conducted between 2008 and 2014 and included a total of 246 participants with 10-64 participants per study. The duration of each intervention ranged from 1.5 h to 28 days. Inorganic nitrate and beetroot consumption was associated with an improvement in vascular function (SMD 0.36; 95 % CI 0.16, 0.56; P < 0.001). The effect on EF was significantly associated with the dose of inorganic nitrate ( β = 0.04, SE = 0.01, P < 0.001), age ( β = −0.01, SE = 0.004, P = 0.02), baseline BMI ( β = −0.04, SE = 0.02, P = 0.05) and systolic BP ( β = −0.01, SE = 0.005, P = 0.02).

CONCLUSIONS:

Inorganic nitrate and beetroot supplementation was associated with beneficial effects on EF. These effects appear to be reduced in older subjects and in subjects with greater cardiometabolic risk.

Pre-eclampsia is a serious condition that typically affects pregnant women after the 20th week of pregnancy, characterized by high blood pressure and damage to organs such as the kidneys and liver. Currently, treatment options are limited, which has prompted researchers to explore alternative approaches. One such promising alternative is dietary nitrate found in vegetables like beetroot, as nitrate can be converted into nitric oxide in the body, which helps lower blood pressure. This study aims to determine the acute effects of nitrate-rich beetroot juice on blood pressure, several blood and salivary markers in pregnant women with pre-eclampsia. Furthermore, the study will assess fetal blood flow using Doppler ultrasound. The investigators want to understand the kinetics of nitrate and nitric oxide metabolites and assess the temporal dependency of the hypotensive response. Through this investigation, the investigators seek evidence of nitrate-enriched beetroot juice as an adjunct therapy in managing pre-eclampsia.

The purpose of the present study is to explore the effects of a dietary nitrate supplement (i.e., beetroot juice) on nitric oxide levels, immunity, mood, and cardiovascular activity during and following final exam stress in healthy individuals.

PURPOSE:

This study tested the hypothesis that nitrate (NO3-) supplementation would improve performance during high-intensity intermittent exercise featuring different work and recovery intervals.

METHOD:

Ten male team-sport players completed high-intensity intermittent cycling tests during separate 5-day supplementation periods with NO3 (-)-rich beetroot juice (BR; 8.2 mmol NO3- day(-1)) and NO3 (-)-depleted beetroot juice (PL; 0.08 mmol NO3- day(-1)). Subjects completed: twenty-four 6-s all-out sprints interspersed with 24 s of recovery (24 × 6-s); seven 30-s all-out sprints interspersed with 240 s of recovery (7 × 30-s); and six 60-s self-paced maximal efforts interspersed with 60 s of recovery (6 × 60-s); on days 3, 4, and 5 of supplementation, respectively.

RESULT:

Plasma [NO2-] was 237% greater in the BR trials. Mean power output was significantly greater with BR relative to PL in the 24 × 6-s protocol (568 ± 136 vs. 539 ± 136 W; P < 0.05), but not during the 7 × 30-s (558 ± 95 vs. 562 ± 94 W) or 6 × 60-s (374 ± 57 vs. 375 ± 59 W) protocols (P > 0.05). The increase in blood [lactate] across the 24 × 6-s and 7 × 30-s protocols was greater with BR (P < 0.05), but was not different in the 6 × 60-s protocol (P > 0.05).

CONCLUSION:

BR might be ergogenic during repeated bouts of short-duration maximal-intensity exercise interspersed with short recovery periods, but not necessarily during longer duration intervals or when a longer recovery duration is applied. These findings suggest that BR might have implications for performance enhancement during some types of intermittent exercise.

CONTEXT:

Beetroots have antioxidant and anti-inflammatory properties, which may help attenuate inflammation and oxidative stress, enhancing recovery from exercise-induced muscle damage (EIMD).

OBJECTIVE:

To evaluate the effects of beetroot supplementation on oxidative stress, inflammation, and recovery after EIMD.

DATA SOURCES:

SPORTDiscus, PubMed, Web of Science, and Scopus databases were searched, and hand-searching was performed by looking to relevant studies that were cited in other studies.

STUDY SELECTION:

For a study to be included in this review, the following inclusion criteria had to be met: (1) research conducted with human participants, (2) original articles in peer-reviewed publications, (3) original studies that had investigated beetroot supplementation intervention on muscle damage and recovery, (4) research conducted with 1 control/placebo group, and (5) articles published from inception to October 2020.

STUDY DESIGN:

Systematic review using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement.

LEVEL OF EVIDENCE:

Level 3.

DATA EXTRACTION:

Two of the 4 authors independently extracted data and assessed the methodological quality of the articles with the PEDro scale. All discrepancies were resolved through a consensus meeting.

RESULTS:

A total of 9 studies were included in this review. The methodological quality of the included studies ranged from moderate to high. Most of the studies found a better recovery of functional variables and muscle soreness, but improvements in markers of muscle damage, inflammation, and oxidative stress were not reported.

CONCLUSION:

The existing evidence suggests that a short-term beetroot supplementation has the potential to accelerate recovery of functional measures and muscle soreness, but further research is needed to clarify if a longer supplementation period (with some days before exercise and some days after) could also promote recovery of markers of muscle damage, inflammation, and oxidative stress.