Journal Title (Medline/Pubmed accepted abbreviation):J. Acad. Nutr. Diet.
Page numbers: 548-552
Summary of Background and Research Design
Background: Nitrates are used to preserve foods such as bacon and sausage and have been identified as potential cancer-causing agents in these foods. However, recently, beetroot juice, which is naturally high in nitrates, has been shown to enhance endurance performance. It is thought that nitrates in the juice are converted to nitric oxide, especially during conditions of low oxygen (e.g. running). Therefore, it is important to determine which food sources of nitrates aid in performance.
Hypothesis:Nitrates from vegetables will improve endurance. Specifically, whole beetroots (high nitrate concentration) will improve performance during a 5-km run compared to cranberry sauce (negligible nitrates present).
Subjects:Men (5) and women (6) age 25 ± 4 y
Experimental design: randomized, double-blinded, placebo-controlled crossover trial
Treatments : Nitrate: Baked beetroot (200 g) with lemon juice, and spices for flavoring
Placebo: Cooked cranberries with added sugar and flavoring to yield the similar nutrient profile
Protocol : The participants arrived at the laboratory and consumed the test meal (either the beetroot or the cranberries). One hour later, blood pressure was measured and the participant began warming up by stretching or walking on the treadmill. Exactly 75 min after they began the meal, they ran on the treadmill at a self-selected pace for 5 kilometers (5 K). Heart rate and perceived exertion were recorded after each mile (1.6 km) and at the end of the 5 K.
Summary of Research Findings
- The participants averaged a faster 5 K after consuming beetroots compared to cranberries (12.3 ± 2.7 km/h with beetroot vs. 11.9 ± 2.6 km/h with the placebo), although it was not statistically significant. However, the subjects did run the last 1.1 miles of the 5K significantly faster in the beetroot group vs. placebo.
- Although the average speed was similar for the first mile, the perceived rate of exhaustion was lower during this leg, suggesting that they might have been able to run even faster.
- Average heart rate was not different between the two trials.
Key practice applications
Vegetable sources of nitrites such as beetroot may improve exercise capacity during endurance events.
Nitrate concentrations were not measured in this study, only calculated from previous studies. There is a chance that the amount of nitrate was much higher or lower than the researchers expected.
- There are other components of beetroot that are not present in cranberry that may have impacted performance instead of nitrates or in addition to nitrates. (Or there could have been components of cranberries that hinder performance.) In studies of beetroot juice supplementation, authors can use a “de-nitrated” beetroot juice that is identical in every other way to beetroot juice.