Fat. Not all fat is the same. While bad fats can wreck your diet and increase your risk of certain diseases, good fats protect your brain and heart. In fact, healthy fats—such as omega-3s—are vital to your physical and emotional health. Including more healthy fat in your diet can help improve your mood, boost your well-being, and even trim your waistline. Learn more »
There are thousands of dietary supplements on the market, including 40+ essential nutrients alone and in various combinations, i.e. vitamins, minerals, trace elements and fatty acids. However, a number of other nutrients are "conditionally essential", meaning that the body normally can make these molecules, but some people do not make optimal amounts. Examples are L-carnitine, alpha-lipoic acid, the methyl donor betaine,  chondroitin sulfate, coenzyme Q10, choline, amino acids such as tyrosine or arginine, and "essential" sugars normally formed in the body. 
"Often the enthusiasm for these vitamins and supplements outpaces the evidence. And when the rigorous evidence is available from randomized controlled trials, often the results are at odds with the findings of the observational studies," explains Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital, professor of medicine at Harvard Medical School, and principal investigator of a large randomized trial known as VITAL (Vitamin D and Omega-3 Trial).
Specialty products may offer particular health benefits or are targeted for specific conditions. These products may consist of whole foods or may be isolated compounds from natural or synthetic sources. Examples include antioxidants, probiotics (supplements containing friendly bacteria for the digestive tract), digestive enzymes, shark cartilage, or other animal products, or chemical extracts such as the hormone DHEA (dehydroepiandrosterone) and coenzyme Q10, an antioxidant.
Most vegetarians eat milk products and eggs, and as a group, these lacto-ovo-vegetarians enjoy good health. A healthful vegetarian diet falls within the food pyramid guidelines offered by the USDA. However, meat, fish and poultry are major sources of iron, zinc and B vitamins, so pay special attention to these nutrients. Vegans (those who eat only plant-based food) should consult a health care professional about adding vitamin and mineral supplements; make sure you consume sufficient quantities of protein, vitamin B12, vitamin D and calcium.
Focus on the long term. Diets fail when people fall back into poor eating habits; maintaining weight loss over the long term is exceedingly difficult. Most people regain the weight they've lost. In fact, some studies indicate that 90 to 95 percent of all dieters regain some or all of the weight originally lost within five years. Your program should include plans for ongoing weight maintenance, involving diet, exercise and a behavioral component. While there are some physical reasons for obesity, there are also behavioral reasons for excessive eating. For example, many women use food as a source of comfort (perhaps to deal with stress). For these women, a weight loss program with a behavioral component will offer alternatives to replace food in this role.
Grains, vegetables and fruits are essential to getting the vitamins, minerals, complex carbohydrates (starch and dietary fiber) and other nutrients you need to sustain good health. Some of these nutrients may even reduce your risk of certain kinds of cancer. But experts say we rarely eat enough of these foods. To make matters worse, we also eat too much of unhealthy types of food, including fat (and cholesterol), sugar and salt.
Nutritional supplements may be designed to provide specialized support for athletes. Some of these consist of high-protein products, such as amino acid supplements, while other products contain nutrients that support metabolism, energy, and athletic performance and recovery. People engaging in intense athletic activity may have increased needs for water-soluble vitamins, antioxidants, and certain minerals, including chromium. Sports drinks contain blends of electrolytes (salts) that the body loses during exertion and sweating, as well as vitamins, minerals, and performance-supporting herbs.