Beets provide a number of health benefits through their high fiber and polyphenols that help to prevent diseases such as cancer and heart disease. On top of these benefits, beets are absolutely loaded in compounds called nitrates that help give you a boost during your workout.
One review of studies found that when consumed, beetroot juice improved time-to-exhaustion and cardiorespiratory performance. (1) Nitrates, like those found in beets, have a really beneficial effect on your blood vessels. Nitrates are converted into nitric oxide, which promotes vasodilation of blood vessels. Simply put it, this means your blood vessels open up wider, which promotes an increased blood flow to allow more oxygen to fuel your cells. Optimal performance was found to be 2-3 hours after consumption, so it is recommended you consume beetroot juice ~90 minutes before your workout.