Phytoestrogens and Their Biological Activities

Phytoestrogens

• Bind to mammalian estrogen receptors and have effects similar to endogenous estrogens
• Isoflavones: found almost exclusively in soybeans and soybean products (e.g. genistin, daidzin)
• Lignans: found in a wide variety of plant-based foods, including seeds, whole grains, legumes, fruit, and vegetables
• Possible role in prevention of hormone-associated cancers, osteoporosis, cardiovascular disease, and menopausal symptoms

Saponins

• Rich food source: legumes
• May have beneficial effects on blood cholesterol levels, cancer, bone health, and stimulation of the immune system

Glucosinolates

• Food source: Cruciferae (e.g. cabbage, broccoli, cauliflower, turnip)
• Sulphoraphane: has anticarcinogenic and antioxidant effects

Monoterpenes

• Active substances in herbs and spices (e.g. menthol, limonene)
• Biological activity: limonene is an anticarcinogen

Polyphenols

• Flavonoids: found in fruit, vegetables, chocolate, wine, and tea
• Phenolic acids: hydroxycinnamic acids (e.g. p-coumaric, caffeic, ferulic, and sinapic acids)
• Stilbenes: Resveratrol
• Flavonoid contents of green leafy vegetables increase with ripeness
• Quercetin is the most common dietary flavonoid

Resveratrol

• A class of polyphenolic compounds called stilbenes
• Food sources: peanuts, grapes, red wine, and some berries
• Low bioavailability
• Health effects: prevention and/or treatment of cancer, cardiovascular disease, and neurodegenerative diseases

Phytosterols

• Collective term for plant-derived sterols and stanols
• Structurally related to cholesterol
• Good food sources: natural sources such as unrefined vegetable oils, whole grains, nuts, and seeds
• The most abundant sterols in plants are β-sitosterol, campesterol, and stigmasterol

Classification of Phytochemicals

• Based on physiological effect and chemical structure
• Categories: Carotenoids, Polyphenols, Phytosterols, Phyto-estrogens, Glucosinolates, Saponins, and others

Carotenoids

• Food sources: widespread in fruits and vegetables (red and yellow pigments)
• Only 40-50 are significant for human nutrition
• Two types: oxygen-free (heat-stable) and oxygen-containing (heat-sensitive)
• The most important carotenoids in diets: α-carotene, β-carotene, lycopene, β-cryptoxanthin, lutein, and zeaxanthin

Phytochemicals

• Approximately 10,000 phytochemicals have been identified, with an estimated 60,000-100,000 remaining unknown.
• A mixed diet contains around 1.5 g of secondary plant metabolites.
• The beneficial effects of phytochemicals are thought to result from the synergistic actions of multiple constituents.

Classification of Phytochemicals

• Based on physiological effect and chemical structure, phytochemicals can be classified into:
  • Carotenoids
  • Polyphenols (flavonoids and phenolic acids, including resveratrol)
  • Phytosterols
  • Phyto-estrogens (isoflavones and lignans)
  • Glucosinolates (sulforaphane)
  • Saponins, protease inhibitors, monoterpenes, and sulphides

Color Examples

• Red foods provide lycopene.
• Yellow-green foods provide zeaxanthin.
• Red-purple foods contain anthocyanin.
• Orange foods contain β-carotene.
• Orange-yellow foods provide flavonoids.
• Green foods provide glucosinolate.
• White-green foods provide allyl sulfides.

Carotenoids

• Carotenoids are widespread in fruits and vegetables and provide red and yellow pigments essential for photosynthesis.
• Only 40-50 carotenoids are significant for human nutrition.
• There are two types of carotenoids: oxygen-free (heat-stable) and oxygen-containing (heat-sensitive).
• The most important carotenoids in diets are:
  • α-carotene
  • β-carotene
  • Lycopene
  • β-cryptoxanthin
  • Lutein
  • Zeaxanthin

Phytochemicals and Functional Foods

• Phytochemicals are bioactive compounds found in plants that may provide health benefits but are not considered essential nutrients.
• Functional foods are rich in phytochemicals and provide health benefits beyond those provided by their nutrients.
• The interest in functional foods began in Japan in the early 1980s.

Definition and Classification of Phytochemicals

• Phytochemicals are physiologically active non-nutrient compounds found in certain plant foods.
• They provide health benefits, are essential for plant interaction with the environment, and confer tastes, aromas, color, and other characteristics to foods.

Physiological Effects of Phytochemicals

• Major effects of phytochemicals include:
  • Anticarcinogenic effects
  • Antioxidative effects
  • Immunomodulatory effects
  • Antimicrobial effects
  • Cholesterol-lowering effects
• Phytochemicals may affect drug metabolism.

Chocolate

• Cocoa is an important source of polyphenols (12-18% total weight).
• Major phenolic compounds in chocolate are the flavanols: catechin, epicatechin, and proanthocyanidins.
• Flavanols are a promising nutritional intervention for reducing the risk of cardiovascular disease.