The transition from an existence as hunter and gatherers to urban agriculture around 10,000 years ago began an epoch when foods were mass-produced but had lower nutritional density, compared with the previous food eaten by our ancestors. The nutritional density in many foods has fallen significantly since human societies transformed from hunter-gatherers into resident farmers. This is especially true in the last 60-70 years after agriculture was changed from small, versatile ecologically driven family farms to large, chemical-based, industrial agriculture.  The reduction of nutritional content in modern crops, compared with older varieties, is well documented.  It is a consequence of soil erosion, loss of essential minerals from continual heavy use, combined with breeding of new varieties, which has increased the size and growth rate of plants by increasing the content of sugar and water and decreasing their mineral content compared to ancient species. At the same time, the relative content of other macronutrients (fat, protein/amino acids) and antioxidants may have been reduced.
Although canola oil appears to be good for the cardiovascular system, two Harvard studies have raised concerns that ALA might be bad for the prostate. In 1993, the Health Professionals Follow-up Study of 47,781 men published a major evaluation of dietary fat and prostate cancer. It found that saturated fat from animal sources such as red meat and whole-fat dairy products was linked to a 2.6-fold increase in prostate cancer. But the study also provided some disquieting news about ALA: Men who consumed the most ALA were 3.4 times more likely to be diagnosed with prostate cancer than those who had the lowest dietary intake.
Eating a healthy diet doesn’t have to be overly complicated. While some specific foods or nutrients have been shown to have a beneficial effect on mood, it’s your overall dietary pattern that is most important. The cornerstone of a healthy diet pattern should be to replace processed food with real food whenever possible. Eating food that is as close as possible to the way nature made it can make a huge difference to the way you think, look, and feel.
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. 
The average American diet leaves a lot to be desired. Research finds our plates lacking in a number of essential nutrients, including calcium, potassium, magnesium, and vitamins A, C, and D. It's no wonder that more than half of us open a supplement bottle to get the nutrition we need. Many of us take supplements not just to make up for what we're missing, but also because we hope to give ourselves an extra health boost—a preventive buffer to ward off disease.
In the same year, the European Food Safety Authority also approved a dietary supplement health claim for calcium and vitamin D and the reduction of the risk of osteoporotic fractures by reducing bone loss. The U.S. FDA also approved Qualified Health Claims (QHCs) for various health conditions for calcium, selenium and chromium picolinate. QHCs are supported by scientific evidence, but do not meet the more rigorous “significant scientific agreement” standard required for an authorized health claim. If dietary supplement companies choose to make such a claim then the FDA stipulates the exact wording of the QHC to be used on labels and in marketing materials. The wording can be onerous: "One study suggests that selenium intake may reduce the risk of bladder cancer in women. However, one smaller study showed no reduction in risk. Based on these studies, FDA concludes that it is highly uncertain that selenium supplements reduce the risk of bladder cancer in women."
In the United States, the National Health and Nutrition Examination Survey (NHANES) has investigated habits of using dietary supplements in context of total nutrient intakes from the diet in adults and children. Over the period of 1999 to 2012, use of multivitamins decreased, and there was wide variability in the use of individual supplements among subgroups by age, sex, race/ethnicity, and educational status. Particular attention has been given to use of folate supplements by young women to reduce the risk of fetal neural tube defects.
If you do decide to diet, you still need to maintain good nutrition. You want to cut back on calories, not nutrients. And while you want to reduce fat, don't eliminate it entirely. Some studies suggest that older women who maintain a higher body-fat percentage are less likely to suffer from osteoporosis and other conditions associated with menopause. Fat cells also retain estrogen, which helps maintain the calcium in your bones. Younger women should be careful, too: a low body fat percentage can lead to infertility; below 17 percent may lead to missed periods, also known as amenorrhea.
^ MacLean CH, Newberry SJ, Mojica WA, Khanna P, Issa AM, Suttorp MJ, Lim YW, Traina SB, Hilton L, Garland R, Morton SC (2006-01-25). "Effects of omega−3 fatty acids on cancer risk: a systematic review". JAMA: The Journal of the American Medical Association. 295 (4): 403–415. doi:10.1001/jama.295.4.403. hdl:10919/79706. PMID 16434631. Retrieved 2006-07-07.
You can get calcium from dairy products like milk, yogurt and cheese, canned fish with soft bones (sardines, anchovies and salmon; bones must be consumed to get the benefit of calcium), dark-green leafy vegetables (such as kale, mustard greens and turnip greens) and even tofu (if it's processed with calcium sulfate). Some foods are calcium-fortified; that is, they contain additional calcium. Examples include orange juice, certain cereals, soy milk and other breakfast foods. Talk to your health care professional about whether you should take calcium supplements if you don't think you're getting enough calcium from food sources.
Substances which the FDA regulates as food are subdivided into various categories, including foods, food additives, added substances (man-made substances which are not intentionally introduced into food, but nevertheless end up in it), and dietary supplements. The specific standards which the FDA exercises differ from one category to the next. Furthermore, the FDA has been granted a variety of means by which it can address violations of the standards for a given category of substances.