More rigorously, nutraceutical implies that the extract or food is demonstrated to have a physiological benefit or provide protection against a chronic disease.
Functional foods are defined as being consumed as part of a usual diet but are demonstrated to have physiological benefits and/or reduce the risk of chronic disease beyond basic nutritional functions.
Examples of claims made for nutraceuticals are resveratrol from red grape products as an antioxidant, soluble dietary fiber products, such as psyllium seed husk for reducing hypercholesterolemia, broccoli (sulforaphane) as a cancer preventative, and soy or clover (isoflavonoids) to improve arterial health. Such claims are being researched and many citations are available via PubMed to ascertain their foundation of basic research.
However, among the above examples, only the effect provided by psyllium as a fiber product has been sufficiently documented in human clinical trials to receive approval by the United States Food and Drug Administration for health claim statements on product labels.
Other nutraceutical examples are flavonoids antioxidants, alpha-linolenic acid from flax seeds, beta-carotene from marigold petals, anthocyanins from berries, etc. With the US Dietary Supplement Health and Education Act (DSHEA), several other compounds were added to the list of supplements originally mentioned in FDA notification. Thus, many botanical and herbal extracts such as ginseng, garlic oil, etc. have been developed as nutraceuticals.
Very few of these products, however, have sufficient scientific evidence proving health benefits to consumers. Consequently, few have FDA approval for making health claims on product labels.