A. FUNDAMENTALS OF FUNCTIONAL FOODS
1. Hippocrates and Food as Medicine
Hippocrates is traditionally associated with the principle that diet and health are closely related. Modern nutrition science evaluates food-health relationships through biochemical, physiological, epidemiological, and clinical evidence.
2. Functional Foods
Functional foods are foods that provide their normal nutritional value together with potentially beneficial physiological effects associated with specific components or characteristics. There is no single universally accepted international legal definition of “functional food.”
3. Development of the Functional Food Concept
The modern functional-food concept developed strongly in Japan during the 1980s. Japan subsequently established regulatory systems for health-related food claims, including the Food for Specified Health Uses (FOSHU) system.
4. Types of Functional Foods
Functional foods may include conventional foods naturally containing bioactive compounds, foods modified through fortification or enrichment, and foods formulated with specific ingredients intended to provide a physiological benefit.
5. Bioactive Components
Important food bioactive components include probiotics, prebiotics, dietary fibre, omega-3 fatty acids, phytochemicals, polyphenols, carotenoids, phytosterols, selected proteins and peptides, vitamins, and minerals.
6. Functional Foods and Supplements
Functional foods are consumed as foods within the normal diet. Food supplements are concentrated sources of nutrients or other physiologically active substances presented in dose forms such as capsules, tablets, or measured liquids.
7. Omega-3 Fatty Acids
Long-chain omega-3 polyunsaturated fatty acids, particularly EPA and DHA, are important bioactive components found in foods such as fatty fish and some marine-algal products.
8. EPA and DHA
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are long-chain omega-3 fatty acids. They participate in several physiological processes and are important components of research on cardiovascular, neurological, and developmental health.
9. DHA in Cell Membranes
DHA is an important structural fatty acid in phospholipids of cell membranes and is particularly abundant in tissues such as the brain and retina.
10. Safety of Omega-3 Supplementation
The safety of EPA and DHA depends on the dose, chemical form, population, duration of intake, and source. A universal statement that supplementation should never exceed a fixed value is scientifically inappropriate because safety assessments are jurisdiction- and population-specific. EFSA’s current assessment, for example, retains a safe level of 1 g/day for supplemental DHA alone while noting that no tolerable upper level could be established from available data.
B. PROBIOTICS AND PREBIOTICS
11. Probiotics
Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The effect is strain-specific and must be supported by appropriate evidence.
12. Probiotic Microorganisms
Commonly studied probiotic organisms include selected strains of Lactobacillus, Bifidobacterium, Saccharomyces, and other microorganisms. The probiotic property cannot be assigned to an entire species without evidence for the particular strain.
13. Health Applications of Probiotics
Probiotic effects have been investigated in areas including gastrointestinal function, immune responses, certain diarrheal conditions, and other health outcomes. Benefits depend on the specific strain, dose, population, and clinical outcome.
14. Prebiotics
A prebiotic is a substrate that is selectively utilized by host microorganisms and confers a health benefit. This modern definition is broader than the older concept of prebiotics being limited to non-digestible carbohydrates in the colon.
15. Common Prebiotic Substrates
Examples of compounds studied as prebiotics include inulin-type fructans, fructooligosaccharides (FOS), galactooligosaccharides (GOS), and certain other selectively utilized substrates. A compound should not automatically be called a prebiotic without evidence of selective utilization and associated health benefit.
16. Fermentation of Prebiotic Substrates
Microbial fermentation of suitable carbohydrates and fibres in the large intestine can produce metabolites including the short-chain fatty acids acetate, propionate, and butyrate.
17. Short-Chain Fatty Acids
Acetate, propionate, and butyrate are important microbial fermentation products. They participate in host-microbe interactions and influence intestinal and metabolic physiology.
18. Synbiotics
Synbiotics are combinations of live microorganisms and substrates that are selectively utilized by host microorganisms and provide a demonstrated health benefit. Their effects depend on the specific components and their interaction.
19. Fermented Foods and Probiotics
A fermented food is not automatically a probiotic food. Fermented foods may contain live microorganisms, inactive microorganisms, or microbial metabolites, whereas the term probiotic requires evidence that the specified live microorganism provides a health benefit.
20. Functional Food and Gut Health
Functional-food research frequently examines interactions among diet, intestinal microorganisms, microbial metabolites, intestinal barrier function, immune responses, and host metabolism. Health effects should be evaluated using appropriate human evidence rather than assumed from laboratory findings alone.
C. POLYPHENOLS AND PHYTOCHEMICALS
21. Polyphenols
Polyphenols are a broad group of plant-derived compounds that includes flavonoids, phenolic acids, stilbenes, lignans, and other phenolic substances. They occur in fruits, vegetables, tea, cocoa, coffee, grains, nuts, and other plant foods.
22. Flavonoids
Flavonoids are a major class of polyphenols. Important subclasses include flavanols, flavonols, flavones, flavanones, anthocyanins, and isoflavones.
23. Quercetin
Quercetin is a flavonol found in foods such as onions, apples, berries, and several other plant foods. Its antioxidant and other biological activities have been extensively investigated, but food-based effects should not be equated automatically with clinical treatment effects.
24. Catechins in Green Tea
Green tea contains several catechins, including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG). EGCG is one of the major catechins studied in green tea.
25. Resveratrol
Resveratrol is a stilbene polyphenol found in grape skins, red grapes, and some other plant sources. It has been investigated for antioxidant and other biological activities.
26. Polyphenols and Oxidative Processes
Many polyphenols can act as antioxidants in chemical and experimental systems. However, antioxidant activity measured in vitro does not by itself establish a clinically meaningful health effect in humans.
27. Polyphenols and Cardiovascular Research
Polyphenol-rich foods and specific polyphenols have been investigated for potential effects on vascular function, oxidative processes, blood lipids, and inflammatory pathways. Human evidence varies according to the compound, food source, dose, and study design.
28. Phytochemicals
Phytochemicals are naturally occurring chemical compounds produced by plants. The term includes many substances with biological activity, including polyphenols, carotenoids, phytosterols, glucosinolates, and other plant metabolites.
29. Phytochemicals and Health
Phytochemicals may influence biological pathways related to oxidative stress, inflammation, cellular signaling, and metabolism. Evidence for disease prevention must be established through appropriate human studies.
30. Flavonoids and Vitamin C
Flavonoids and vitamin C commonly occur together in many fruits and vegetables. Experimental interactions have been investigated, but broad claims that flavonoids universally “enhance” vitamin C should not be treated as established clinical fact.
D. SOY ISOFLAVONES AND PHYTOESTROGENS
31. Soy Isoflavones
Soybeans and soy foods contain the isoflavones genistein, daidzein, and glycitein. These compounds can interact with estrogen receptors and are therefore classified as phytoestrogens.
32. Sources of Soy Isoflavones
Important dietary sources include soybeans, tofu, tempeh, miso, soy beverages, and other soy-derived foods. Concentrations vary according to soybean variety and processing.
33. Biological Activity of Isoflavones
Isoflavones have estrogen-receptor-related biological activity, but their physiological effects differ from those of endogenous human estrogen. Health outcomes depend on dose, exposure period, age, sex, and individual physiology.
34. Soy and Cardiovascular Health
Soy foods and soy protein have been studied for their effects on blood lipid profiles and cardiovascular risk. Evidence should be interpreted according to the specific soy product and outcome being evaluated rather than attributing all effects to isoflavones alone.
35. Soy and Bone Health
Soy protein and isoflavones have been investigated in relation to bone health. Results vary among populations and study designs, so they should not be presented as a universal treatment for osteoporosis.
36. Soy and Menopausal Symptoms
Soy isoflavones have been studied for their potential effects on menopausal symptoms, particularly vasomotor symptoms. Evidence is variable, and effects may differ according to preparation, dose, and individual characteristics.
E. CAROTENOIDS
37. Dietary Carotenoids
Important dietary carotenoids include β-carotene, α-carotene, β-cryptoxanthin, lycopene, lutein, and zeaxanthin. They occur widely in fruits and vegetables.
38. Provitamin A Carotenoids
Some carotenoids can be converted into vitamin A. Important provitamin A carotenoids include β-carotene, α-carotene, and β-cryptoxanthin. Lycopene, lutein, and zeaxanthin do not function as vitamin A precursors.
39. Beta-Carotene
Beta-carotene is a carotenoid with provitamin A activity. Its conversion to vitamin A is regulated by physiological needs, so high dietary β-carotene exposure does not produce vitamin A toxicity in the same manner as excessive preformed vitamin A.
40. Carotenemia
High intake of carotenoid-rich foods or supplements can cause carotenemia, a reversible yellow-orange coloration of the skin. It is generally associated with high circulating carotenoid concentrations rather than vitamin A toxicity.
41. Lycopene
Lycopene is a non-provitamin A carotenoid found in foods such as tomatoes, watermelon, and pink grapefruit. Its biological activities have been investigated in relation to oxidative processes and several chronic disease outcomes.
42. Lutein and Zeaxanthin
Lutein and zeaxanthin are xanthophyll carotenoids concentrated in the retina, particularly the macula. They are important subjects of research concerning visual and retinal health.
43. Xanthophylls
Xanthophylls are oxygen-containing carotenoids. Examples include lutein, zeaxanthin, β-cryptoxanthin, and other oxygenated carotenoids.
44. Carotenoids and Skin
Some dietary carotenoids accumulate in skin and can influence skin coloration and antioxidant systems. Evidence concerning protection from ultraviolet radiation depends on the specific carotenoid, dose, duration, and overall diet.
F. PHYTOSTEROLS AND OTHER BIOACTIVE COMPOUNDS
45. Phytosterols
Phytosterols are plant sterols structurally related to cholesterol. Important examples include β-sitosterol, campesterol, and stigmasterol.
46. Phytosterols and Cholesterol Absorption
Phytosterols can reduce intestinal absorption of dietary and biliary cholesterol by competing with cholesterol in intestinal mixed micelles. Regular intake of appropriate amounts of plant sterols or stanols can reduce LDL-cholesterol in appropriate dietary contexts.
47. Anthocyanins
Anthocyanins are water-soluble flavonoid pigments responsible for many red, purple, and blue colors in fruits and vegetables. Their potential effects on cardiovascular, metabolic, and cognitive health are under active scientific investigation.
48. Hesperidin
Hesperidin is a flavanone glycoside found particularly in citrus fruits. It has been investigated for vascular, antioxidant, and metabolic effects, but specific therapeutic claims require appropriate human evidence.
49. Tangeretin
Tangeretin is a polymethoxylated flavone found mainly in citrus peels. Experimental studies have investigated its effects on cellular signaling and cancer-related pathways, but laboratory findings should not be interpreted as proof of cancer treatment or prevention in humans.
50. Evidence-Based Use of Functional Foods
Functional foods should be evaluated according to the specific food, bioactive component, dose, bioavailability, target population, safety, and quality of human evidence. A biochemical or laboratory effect does not automatically establish a disease-prevention or therapeutic effect. Health claims should be supported by appropriate scientific evidence and comply with the applicable regulatory framework.