About half of all Americans take a daily multivitamin as a way to improve their health and cut their risk of diseases. But experts now say that - in almost all cases - the best way to get a full dose of vitamins is from nutritious foods rather than from pills. There is a lot of scientific evidence showing diets rich in produce, nuts, whole grains and fish promote health and decrease risk of heart disease, stroke, diabetes and cancer, according to a new Vitamins and Minerals" report from Harvard Medical School. On the other hand, studies involving vitamin supplements - and there have been many - show mixed results. In fact, after reviewing a large body of research in 2006, the National Institutes of Health decided not to definitively rule for or against multivitamins' ability to prevent diseases. So what are the quickest ways to boost the vitamin content in your meals? The report identifies about three dozen foods that have the most nutrients per calorie, including avocados, berries, cantaloupe, dark leafy greens, eggs, yogurt, lentils, beans, almonds, fish, chicken and turkey. And although most people think of citrus as the best source of vitamin C, a red pepper has twice as much as an orange. Similarly, potatoes and white beans have more potassium than bananas. The final advice from Dr. Dariush Mozaffarian, the report's editor: "Spend your time and money improving your diet, which is far more likely to pay off in the long run than popping a pill."