“Bears. Beets. Battlestar Galactica.”
If you watched The Office on NBC, you may recognize this as one of the more memorable lines spoken by the show’s protagonist, Jim Halpert. But is there any chance that consuming beets might help you out with strenuous physical tasks, such as battling a bear?
It’s uncertain if that’s how this line of research began, but it began nonetheless. Over the last decade, numerous researchers have been investigating the effects of beetroot juice on exercise performance. The primary active ingredient is dietary nitrate, which promotes nitric oxide (NO) production in the following series of reduction reactions:
Nitric oxide boosters are certainly nothing new. About 10-15 years ago, arginine-based NO boosters were exploding onto the scene, with promises of skin-splitting pumps in the gym. The amino acid arginine is a precursor of NO, much like nitrate, but they form NO through separate pathways.
One of the primary issues with arginine supplementation is relatively extensive pre-systemic metabolism; this means that much of the orally-ingested supplement dose gets metabolized and broken down in the gut, and never makes it out to the working muscle. As a result, arginine studies generally show a lack of performance benefits, particularly in well-trained individuals. There are some instances in which arginine has been associated with performance improvements when combined with other ingredients, such as alpha-ketoglutarate [1], but the largely disappointing results of arginine alone have shifted the focus toward other NO boosters.
Nitrates and Endurance Exercise Performance
A growing body of literature suggests that beetroot and other sources of nitrate have favorable effects on aerobic exercise performance. Research has documented enhanced exercise efficiency [2], reductions in muscle fatigue [2], and increased vasodilation to support blood flow during exercise [3]. Collectively, these effects seem to reduce the amount of energy used during submaximal exercise, and help individuals perform at maximal intensities for a longer period of time. For a runner, this means they can go harder and further for longer while using fewer calories. This is a huge advantage for athletes during competition!
Nitrates, Resistance Exercise, and Muscle Growth
This pathway of NO formation is particularly intriguing in the context of resistance training. While the arginine pathway requires oxygen to function, activity of the nitrate pathway is actually increased during hypoxia (low oxygen availability) and acidosis (increased lactic acid production), which are observed during high-intensity exercise like sprinting and lifting weights.
Aside from the previously mentioned effects on muscle fatigue, research indicates that nitrate enhances calcium handling and force production in fast-twitch muscle fibers [4], and reduces soreness after exercise [5]. Taken together, these factors may suggest that the performance benefits of beetroot juice may translate to resistance training as well.
Despite these plausible mechanisms, very little research has been conducted to assess the effects of nitrate on resistance training outcomes. A recent study by Mosher et al. [6] evaluated the effects of beetroot juice on three consecutive sets of bench press. In this study, participants lifted 60% of their one-repetition maximum until they reached failure, rested for two minutes, and repeated this process for three total sets. Compared to a placebo, the participants completed more total repetitions after consuming the beetroot juice. While far more research is needed to confirm these results, they provide preliminary evidence that the performance effects of nitrate can indeed translate into the realm of resistance training.
Our research group previously assessed the effects of pomegranate extract, another source of nitrate, on a single set of bench press taken to failure [7]. Our study showed that the supplement did enhance blood flow, but the improvement in bench press repetitions (+0.63 repetitions, on average) was not statistically significant. Taken together, these results support the notion of using dietary nitrate to facilitate blood flow and muscular endurance during multiple sets of strenuous resistance exercise.
You may be wondering if nitrate supplements increase muscle mass in addition to strength. There are reasons to believe that this is possible; as we just learned, they can enhance your ability to perform more repetitions in the gym, which could enhance muscle growth over time.”
In addition, nitrate reliably increases NO production, and NO can directly influence muscle growth by promoting satellite cell activation [8]. Satellite cell activation is one of the key processes that takes place in the muscle cell and contributes to an increase in the size of the muscle.
As a result, rodent research has shown increased hypertrophic (muscle growth) responses to loading in the presence of NO donors, and reduced muscle growth in the presence of NO blockers. In theory, for the resistance-training athlete, increasing NO production will promote the increase of muscle mass, and blocking the effects of NO will have the opposite effect of decreasing the size of the muscle. Unfortunately, long-term resistance training studies with beetroot or other nitrate sources have not been carried out in humans, so we really can’t confidently draw conclusions about hypertrophy at this time.
What about risks?
Nitrate and nitrite have long been demonized as carcinogenic components of processed meats. There is some scientific basis for this assertion, as nitrate and nitrite can promote the formation of carcinogenic N-nitroso compounds in some contexts.
However, it appears that this commonly discussed cancer link pertains to processed meats more so than overall nitrate intake; it is possible that the way these items are packaged and preserved may increase the formation of N-nitroso compounds in a manner that is not observed with other forms of nitrate/nitrite consumption.
In addition, cancer concerns regarding plant sources of nitrate don’t have much face validity- if there are a few things we know to be associated with pretty good long-term health outcomes, it is plant sources of nitrate and nitrite, such as beets, celery, spinach, and other green leafy vegetables. So, evidence suggests that you can have your beetroot juice and enjoy its blood flow-boosting, bench-bolstering effects without fear. But remember, its effects on bicep-building (and bear-battling) have yet to be conclusively determined.