A spokesperson for optimal nutritional intake is the well-known biochemist Bruce Ames, who proposed the "triage theory of nutrients," in which enzymes responsible for cell maintenance functions evolved to have lower affinity for the essential vitamin and mineral cofactors than the enzymes responsible for short-term survival, to preserve life during times of famine. 
"These products provide a subtle, incremental effect. You can't use a sports supplement for a week and expect to gain pounds of muscle, but if used properly, research shows they can provide a slight, not overwhelming, edge," says Andrew Shoa, PhD, vice president for regulatory affairs for the Council for Responsible Nutrition, a trade association for the dietary supplement industry.
Omega-3 fatty acids are essential for the neurological and early visual development of your baby and for making breast milk after birth. Aim for two weekly servings of cold water fish such as salmon, tuna, sardines, herring, or anchovies. Sardines are widely considered the safest and most sustainable fish to eat, while seaweed is a rich vegetarian source of Omega-3s.
Think smaller portions. Serving sizes have ballooned recently. When dining out, choose a starter instead of an entree, split a dish with a friend, and don’t order supersized anything. At home, visual cues can help with portion sizes. Your serving of meat, fish, or chicken should be the size of a deck of cards and half a cup of mashed potato, rice, or pasta is about the size of a traditional light bulb. By serving your meals on smaller plates or in bowls, you can trick your brain into thinking it’s a larger portion. If you don’t feel satisfied at the end of a meal, add more leafy greens or round off the meal with fruit.
Healthy young people normally make sufficient amounts of conditionally essential molecules in the body, although the levels are not always optimal. With inadequate levels of minerals or vitamins, key enzymes in biochemical pathways may not function optimally. Due to genetic mutations, some enzymes may have increased needs for certain cofactors (vitamins), which can prevent them from functioning optimally. Some enzymes only function normally when supplied with cofactors in greater amounts than normally required. If supplements of essential nutrients prove insufficient for optimal enzyme function, "conditionally essential" nutrients may be added as part of a comprehensive, therapeutic program.
Eat a balance of carbohydrates, proteins and fats at each meal and choose foods rich in fiber, vitamins and minerals. A good way to do this is to fill your plate with 3–4 food groups at each meal. Eat a combination of protein-rich foods, whole grains, dairy, fruits and vegetables, and incorporate the groups you miss into other meals and snacks throughout the day. Stick to healthy portions — see our Essential Guide to Portion Sizes for tips.
Dosages of nutritional supplements vary widely, depending on the product and individual needs. For vitamins and minerals, U.S. RDA's are essential guidelines. For other products, manufacturers' guidelines, consumer information sources such as nutritional books and magazines, and practitioners including nutritionists and naturopathic physicians may be consulted.
Parents and caregivers play a key role in not only making healthy choices for children and teaching children to make healthy choices for themselves. But in today’s busy world, this isn’t always easy. So Let’s Move! offers parents and caregivers the tools, support and information they need to make healthier choices while instilling healthy eating habits in children that will last a lifetime.
Because observational studies may not fully control for dietary factors, exercise habits, and other variables, they can't prove whether the treatment is responsible for the health benefits. "People who take supplements tend to be more health conscious, exercise more, eat healthier diets, and have a whole host of lifestyle factors that can be difficult to control for fully in the statistical models," Dr. Manson says.
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. 
For example, while increased consumption of fruits and vegetables are related to decreases in mortality, cardiovascular diseases and cancers, supplementation with key factors found in fruits and vegetable, like antioxidants, vitamins, or minerals, do not help and some have been found to be harmful in some cases. In general as of 2016, robust clinical data is lacking, that shows that any kind of dietary supplementation does more good than harm for people who are healthy and eating a reasonable diet but there is clear data showing that dietary pattern and lifestyle choices are associated with health outcomes.