Some supplements may have side effects, especially if taken before surgery or with other medicines. Supplements can also cause problems if you have certain health conditions. And the effects of many supplements haven’t been tested in children, pregnant women and other groups. So talk with your health care provider if you’re thinking about taking dietary supplements.
Carbohydrates should provide 45%–65% of your daily calories. Most of those calories should come from the complex carbohydrates in high-fiber and unrefined foods, such as bran cereal and other whole-grain products, brown rice, beans and other legumes, and many fruits and vegetables. These carbohydrates are digested and absorbed slowly, so they raise the blood sugar gradually and don't trigger a large release of insulin. People who eat lots of these foods have higher HDL ("good") cholesterol levels and a lower risk of obesity, diabetes, and heart disease. A good amount of soluble fiber in the diet lowers LDL ("bad") cholesterol, and high-fiber diets reduce the risk of intestinal disorders ranging from constipation and diverticulosis to hemorrhoids. Some studies have shown that fiber may help reduce the risk of colon cancer. Men need more fiber than women: 38 vs. 25 grams a day before the age of 50 and 30 vs. 21 grams a day thereafter.
^ Siscovick DS, Barringer TA, Fretts AM, Wu JH, Lichtenstein AH, Costello RB, Kris-Etherton PM, Jacobson TA, Engler MB, Alger HM, Appel LJ, Mozaffarian D (2017). "Omega-3 Polyunsaturated Fatty Acid (Fish Oil) Supplementation and the Prevention of Clinical Cardiovascular Disease: A Science Advisory From the American Heart Association". Circulation. 135 (15): e867–e884. doi:10.1161/CIR.0000000000000482. PMID 28289069.
For instance, foods rich in vitamin E and beta-carotene are healthy and can help reduce cancer risk. However, the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) recommend against taking vitamin E or beta-carotene for the prevention of cardiovascular disease. People who smoke or are at risk for lung cancer also should avoid beta-carotene. It can increase their risk of lung cancer.
We mean real food as opposed to processed food. Real food is fruits, vegetables, meats, dairy, seafood, nuts, seeds, whole grains and beans. Natural sweeteners, coffee, chocolate and wine count, too — just in moderation. Avoid food that is mass-produced, emulsified (where water and oil don’t separate) or shelf-stable. Eating real food leads to eating more nutrient-rich food without much effort. See What Real Food Looks Like for more information.
If all you have time for is a quick snack from the gas station or drugstore, know that you do have options, and if you know what you're looking for, it will be easier to find. When we asked registered dietitians to recommend snacks to buy at the drugstore, they tended to go for things like nuts and seeds that pack plenty of flavor (hi, wasabi chickpeas), plenty of protein, and not a whole lot else.
Nutritional density varies considerably geographically between different regions, even with the same agricultural methods. This was documented in the United States in 1948 by a researcher at Rutgers University in the so-called Firman Bear report.  At that time agriculture was little mechanized, and artificial fertilizers and pesticides were hardly used. The analysis found large differences in the content of minerals in the same food. The largest variations were found for potassium, sodium, boron and iron in spinach, while the greatest differences in calcium, magnesium and copper content were found in tomatoes.