Dr. Danielle Belardo runs a preventive cardiology practice in Los Angeles. She said it's easier to maintain a high-fiber diet using frozen fruits and vegetables than fresh. Danielle Belardo/Precision Preventive Cardiology Most Americans eat half the recommended daily amount of fiber. A vegan cardiologist eats 90 grams of fiber a day thanks to her plant-based diet. Fiber can lower "bad" cholesterol levels, help you feel full, and reduce the risk of cancer. Most of us don't eat enough fiber. Not Dr. Danielle Belardo, though. She routinely eats a whopping 90 grams a day, more than most Americans get in a working week. "There's no guideline that says anyone should reach 90 grams of fiber a day, it just happens to be what I eat," Belardo, a vegan cardiologist practicing in Los Angeles, told Business Insider. The general recommendation is for fiber to make up 14 grams of each 1,000 calories we consume. That amounts to at least 25 grams a day or the fiber in two cups of black beans.…