The United Healthcare/Pacificare nutrition guideline recommends a whole plant food diet, and recommends using protein only as a condiment with meals. A National Geographic cover article from November 2005, entitled The Secrets of Living Longer, also recommends a whole plant food diet. The article is a lifestyle survey of <answer>three</answer> populations, Sardinians, Okinawans, and Adventists, who generally display longevity and "suffer a fraction of the diseases that commonly kill people in other parts of the developed world, and enjoy more healthy years of life." In sum, they offer <answer>three</answer> sets of 'best practices' to emulate. The rest is up to you. In common with all <answer>three</answer> groups is to "Eat fruits, vegetables, and whole grains."
How many populations were studied and surveyed for the cover article?
three