You must have heard about the benefits of downing beet juice before exercising. It is a popular belief that it increases blood flow and improves performance. A study was conducted at the Penn State's Noll Laboratory to find out the real picture. The results of the study may surprise athletes. Beet juice is definitely rich in nitrates but, they do not seem to enhance muscle blood flow or vascular dilation during exercise. However, researchers did note that beat juice “de-stiffened” the blood vessels under resting conditions and thereby they eased the workload of the heart significantly.
So popular is the trend of drinking beet juice that you will find many endurance athletes consuming this crimson supplement to improve blood and oxygen flow in their muscles during training and competition. Some even think that it can improve their ability to withstand muscle fatigue during repeated bouts of high intensity exercise. In fact, some patients with high blood pressure are asking their doctors if drinking the juice can lower their high blood pressure.
To find out if these potential benefits of beet really hold good, David Proctor, professor of kinesiology and physiology at Penn State, decided to test the ability of the juice to enhance blood flow to exercising muscles. He along with other fellow researchers found that the belief regarding improved muscle blood flow did not hold up to their test. Their findings were reported in the journal Applied Physiology, Nutrition, and Metabolism.
For the study, subjects were given either a placebo drink containing beetroot juice minus the nitrate or a relatively high dose of nitrate-rich beetroot juice. Proctor and his colleagues found that the latter did not enhance the natural rise in blood flow to the forearm muscles during graded handgrip exercise. Jin-Kwang Kim, study's lead author and Penn State physiology graduate student said that the juice had no effect on the dilation of the brachial artery in these volunteers.
Green leafy vegetables like spinach and beetroot are a good source of nitrates. They are converted naturally in the body to nitric oxide – a molecule that relaxes and widens blood vessels and helps the cells in efficiently using oxygen. These days a number of manufacturers liquefy beetroots and concentrate the nitrate into beetroot juice “shots.”
Proctor said that their study was the first of its kind that measured the blood flow to the contracting muscles after consuming nitrate-rich supplements such as beetroot juice. However, in some previous studies, improved muscle oxygenation during exercise after consuming nitrate-rich supplements have been reported.
Proctor said that the breakdown product of the nitrate in the participants’ blood was measured and it indicated that these participants absorbed the nitrate from the drink and converted it to nitrite – the precursor to nitric oxide. They however observed a direct correlation between nitrite levels in the blood and the slowing of participants’ arterial pulsation velocity. It indicates that the supplement did indeed have an artery de-stiffening effect.
Proctor said the reason for the null effects on muscle blood flow observed in this first study could be due to two factors. Firstly, the subjects were young individuals with blood pressure and cholesterol levels in the ‘very healthy’ range. So, it could be that these subjects already had well-preserved vascular endothelial function. The second contributor could be the relatively small range of forearm exercise intensities that were examined in this study. It is possible that any blood flow enhancing effect of dietary nitrate is measurable only during higher intensity and fatiguing work intensities.
Proctor and his colleagues are now working on an investigation of the effects of beet juice on vascular function in older adults who have elevated blood pressure and those whose muscle blood flow during exercise is impaired.