ATHLETE x SCIENCE
Athletes and health enthusiasts alike constantly seek new and improved methods capable of eliciting sports performance and health benefits. The explosion of so-called “super foods” has called individuals to seek ingredient-specific solutions to support or enhance both health and athletic needs. These super ingredients come in whole-food and/or supplement form, based on personal preference. Analyzing the constituent ingredients of foods and their metabolic function within the human body has led to some very powerful discoveries for both the general and athletic populations. Uncovering the synergistic, additive, and/or negative effects of these ingredients has thus become a major focus of nutrition research over the last decade. Moderate evidence exists in support of fish oil, carnitine, Vitamin C, and tart cherry juice supplementation (4). High levels of evidence have been established regarding B-alanine, caffeine, creatinine, and recently, beetroot juice (4).
One of these once elusive power ingredients, nitrate, is a natural constituent of the beetroot plant. Beet root juice, beet powder, beet pill supplements, and the raw vegetable itself have all been disappearing off the supermarket shelves since the research on their many health benefits have gone viral. This article aims to unveil the physiologic mechanisms behind beet’s powerful effects in the human body and why they should become a health food staple in every diet.
Inorganic nitrate (NO3-) is a compound found abundantly in green leafy vegetables and beetroot, carrot and pomegranate juice. Once the nitrate-containing food or supplement is ingested, the inorganic nitrate metabolizes in vivo (within the body) to its bioactive form, nitrite (NO2-), which is then reabsorbed into the bloodstream and sent into circulation (1). The anaerobic bacteria located in the oral cavity, predominantly within the crypts of the tongue, play an integral role in completing this chemical reduction (1). Nitrite is further reduced into various function forms (NOx), including nitric oxide (NO), which exert various physiologic effects on the body. Plasma levels of NO2- have been shown to peak at three hours post-ingestion, and remain elevated for approximately five hours (1).
Nitric oxide plays a biological role in signaling the endothelium (inner lining) of smooth muscles to relax and vasodilate, subsequently enhancing blood flow to nearby tissue. Conditions of low oxygen, such as ischemia and hypoxia, and low pH in body regions promote the reduction of NO2- to NO, favoring its effects in areas of the body most deprived of oxygen and adenosine triphosphate (ATP), the body’s critical energy source. An increase in circulating levels of NO2- and NO protects hypoxic (oxygen-deprived) tissues, including damaged blood vessels and contracting skeletal muscle by improving blood flow to those areas.
The benefits of nitric oxide might invoke the question as to why one cannot supplement NO directly, as opposed to taking the inorganic precursor, however, the endogenous form is a gas produced from the amino acid L-arginine. Research shows that supplementation with L-arginine is also ineffective in elevating the nitric oxide levels in the body; it appears that the endogenous chain of mechanisms is critical for the complete reduction of NO3- to NO for its entry into circulation (1). Considering these physiological mechanisms, recent research efforts have been made to reveal the possible health benefits of nitrates for individuals with blood flow disorders and as an ergonomic aid for athletes.
The epidemic of chronic inflammatory conditions in the U.S. has led to the massive inflation of health care costs, which were estimated at $4 trillion dollars in 2015, or $14,000 per person; in fact, the chronic “lifestyle” diseases like diabetes mellitus, hypertension, and coronary artery disease are responsible for more than 75% of the nation’s annual cost of health care (1). The price of these inflammatory conditions often involves compromised epithelial tissue lining the blood vessels, and a malfunction in maintaining normal homeostatic levels of nitric oxide.
The implementation of Dietary Approaches to Stop Hypertension (DASH) diet largely focuses on the incorporation of nitrates into daily intake, at a rate that is 5-fold higher than the recommendations of the World Health Organization (WHO) (1). The DASH diet has become the gold standard “natural” prescription for individuals diagnosed with chronic disorders of blood flow. Some studies have even proposed that this diet is as efficacious as a single hypertensive agent for reducing blood pressure (1).
Ingestible NO3- can be delivered in the form of beet root juice (500mL or 2 cups), whole beet root, or in supplement form (NaNO3-) at 10mg/kg of body weight (1). Per 100g of fresh weight, leafy greens such as lettuce, spinach, celery, and beetroot typically contain over 250mg of nitrate (2). These unveiled health benefits propose that nitrate supplementation may be a low-cost option for the prevention and/or treatment of blood flow disorders.
Augmenting the bioavailability of nitric oxide will, theoretically, positively influence exercise performance due to its effects on improving mitochondrial respiration, glucose uptake, calcium handling within the muscle fibers, vasodilation, and angiogenesis (the generation of new blood vessels) (2). Nitric oxide delivers a greater amount of oxygenated blood to skeletal muscle by enhancing blood flow to deprived tissues (1). In theory, this increase in blood flow would also improve the perfusion of oxygen and nutrients to exercising muscles, and thereby enhance performance.
Studies have shown that beet root juice consumption delays the onset of VO2 consumption during high intensity exercise, which correlates to a reduced oxygen cost of submaximal exercise and enhanced fatigue tolerance (1). In one particular study, healthy, fit subjects having consumed 200g of baked beetroot (>500mg of NO3-) performed a 5K time trial at a 5% faster running velocity than those ingesting the placebo; additionally, the former group had a considerably lower rate of perceived exertion compared to their placebo counterparts (1). Specifically, conditions of low oxygen supply or delivery and/or low pH (acidic) will greatly promote the reduction of NO2- to NO, and thus enhance oxygen and nutrient delivery to exercising muscles. This piece of physiology is particularly useful for athletes training and/or racing at altitude, considering how hypoxic conditions elicit these deficits within the muscles.
Dietary NO3- has been shown to reduce the metabolic cost of ATP and creatine phosphate production, which would thus improve force production and enhance the efficiency of muscle contractility (1). In one particular study, following three days of NO3- supplementation, the mitochondria of the vastus lateralis [from the quadriceps] muscle were isolated and tested for their efficiency (1). Mitochondria are the energy-producing “powerhouses” of the cell, and are responsible for the generation of ATP through cellular respiration. The NO3- supplemented group yielded a 20% improvement in mitochondrial efficiency and a 45-64% decrease in basal oxygen consumption as compared to the placebo group (1). The efficiency of these cellular organelles is determined by the P/O ratio, which measures the ability of the cell to couple phosphorylation and oxidation; in other words, the ratio compares the number of phosphate molecules incorporated into ATP molecules against the amount of oxygen consumed in the process. Lower P/O ratios indicate poor cellular efficiency, whereas high ratios indicate that more ATP molecules are produced per oxygen reduction to water (oxidation). More ATP means more energy availability to the muscles, and delayed time to fatigue as a result.
Interestingly, the studies which have demonstrated positive results in athletic performance after nitrate supplementation have only been statistically significant in the 'healthy, fit' population, rather than the 'athletic, elite' groups of test subjects. It is suspected that highly-trained athletes, especially endurance athletes, have already established high levels of NO activity through extensive training, rendering nitrate supplementation less than effective (2). These athletic subjects would be expected to have increases in skeletal muscle capillary infiltration, eliminating the need for NO to compensate for hypoperfusion of oxygen and nutrients.
Recent evidence shows that nitrate may preferentially target type II muscle fibers to improve their contractile function under conditions of hypoxia and/or electrolyte deprivation (2). Type II muscle fibers are commonly referred to as the "fast-twitch" or anaerobic fibers, which are selectively recruited during high-intensity bursts of activity such as repeat bouts of sprinting and jumping. These fibers fatigue rather quickly into a state of hypoxia, with energy supplies capping out at roughly 90 seconds, thus indicating the need for nitric oxide's effects.
Speed-power athletes would benefit most from improving the efficiency of Type II fibers in this regard. A double-blind study by Rimer et al., assessed the acute changes in maximal cycling power and optimal pedaling rate in training cyclists (3). The study aimed to investigate whether NO3--rich beetroot juice (BRJ) could improve these power metrics during short bouts of maximum cycling efforts lasting three to four seconds as compared to an NO3--depleted placebo group (3). The tests were performed approximately 2.5-hours post-ingestion of the BRJ, since the effects of nitrates within the body peak between 2.5 and 3 hours, and thus should be ingested at roughly that duration prior to activity in order to elicit maximum effects (1, 3). The results of the study demonstrated that the acute dietary intake of NO3- significantly increased both maximum cycling power and optimal pedaling rate (3). This aspect of nitrate physiology has yet to be thoroughly explored by the research, but provides promising evidence for the speed-power athlete in its novel stages of exploration.
Ingesting dietary NO3- via diets abundant in nitrate-rich vegetables or juice, or by pill supplementation, may offer a low-cost, natural treatment methodology for individuals with blood flow disorders. Those looking to improve athletic performance, such as increasing time to fatigue and improving energy efficiency, can also reap the benefits of nitrate-rich foods. These benefits would be diminished with the use of antibacterial mouthwash or swimming in chlorinated pools, due to reduction of nitrate-reducing bacteria in the mouth; these two conditions should be avoided when trying to maximize the benefits of nitrate supplementation. The dose-dependent effect of nitrate supplementation in elite athletic populations has not been established as efficacious, but is now considered to be well-supported in both the general and fit populations.