Beets are no longer just a niche  health food  — they’re becoming a mainstream staple as demand rises across farms, restaurants and supplements , reflecting a broader shift in how Americans eat . The red, purple or sometimes gold root vegetable — not to be confused with its white cousin, the sugar beet — is low-calorie and packed with nutrients and compounds linked to benefits, ranging from  brain health  to athletic performance. Several studies suggest beets may help lower blood pressure, increase blood flow and protect arteries. “That’s in large part because beets are naturally rich in nitrates, a compound that our bodies convert to nitric oxide, a potent vasodilator that relaxes and widens blood vessels,” as  The Washington Post  recently noted.…