Functional Nutrition Prebiotics and Probiotics What Are They

As other functional components of foods, prebiotics and probiotics may promote healthy bacteria, or microflora, in your intestines-and perhaps improve your health. Prebiotics stimulate or help activate bacteria growth; probiotics are the live cultures, or bacteria, themselves. Synbiotic combines both.

  • Prebiotics are nondigestible substances such as oligosaccharides, inulin, and polydextrose (indigestible carbohydrate) in food that promote the growth of normal, healthful bacteria that are already in your colon. Other substances in food, such as dietary fiber, starch, and sugar alcohols, may work as prebiotics, too.
  • Probiotics are active cultures, such as some strains of lactic acid bacteria, or foods that contain them, that help reintroduce or change bacteria in the intestine. Lactobacilli and Bifidobacteria in yogurt with live cultures and other fermented dairy food and some nondairy foods have probiotic cultures.

Research suggests that probiotic cultures may help keep your immune system healthy and help maintain the "good" bacteria in your intestine. Probiotics also may help reduce the risk of some health problems-for example, shorten the duration of diarrhea, reduce the symptoms of lactose intolerance, decrease the risk of some cancers, help prevent some allergy symptoms, and reduce symptoms of irritable bowel disease, among others.

been studied. What we know today is merely the "appetizer."

Research has revealed a few things. Most fruits and vegetables contain phytonutrients. Different plant-based foods supply different kinds and amounts; some have a remarkable variety. An orange, for example, has more than 170 different phytonutrients! In any fruit or vegetable, these substances appear to work together with nutrients and fiber for your good health.

Check the Appendices, "Functional Foods: What Does Research Say? to learn more.

For phytonutrients, food databases are limited, with only a few key carotenoids and phytoestrogens. A USDA database for flavonoids is being developed.

Functional Nutrition: A Quick Look at Key Phytonutrients

Where They're Found

A Handful of Phytonutrients* What They Appear to Do (some food sources)

Carotenoids

Beta carotene

Lutein

Lycopene

Zeaxanthin

Flavonoids

Anthocyanidins

  • As an antioxidant, neutralizes free radicals that may damage cells
  • Bolsters antioxidant defenses in cells
  • May contribute to maintaining healthy vision
  • May reduce risk of prostate cancer

Flavanols: catechins, epicatechins, procyanidins

Flavanones: hesperetin, naringenin

Flavonols (quercetin)

  • May contribute to maintaining healthy vision
  • As an antioxidant, neutralizes free radicals that may damage cells
  • May contribute to maintaining brain function
  • May contribute to maintenance of healthy immune function
  • May contribute to maintaining heart health
  • Neutralizes free radicals that may damage cells
  • Bolsters antioxidant defenses in cells
  • Neutralize free radicals that may damage cells
  • Bolster antioxidant defenses in cells
  • Yellow-orange fruits and vegetables such as apricots, cantaloupes, papayas, carrots, pumpkins, sweet potatoes, winter squash
  • Green vegetables such as broccoli, spinach, kale
  • Green vegetables such as kale, spinach, collard greens, Swiss chard, Romaine lettuce, broccoli, Brussels sprouts
  • Kiwifruit
  • Egg yolks
  • Most red fruits and vegetables such as tomatoes, processed tomato products, pink grapefruit, guava, watermelon (The red pigment in red peppers is from keto carotenoids, not lycopene.)
  • Corn, spinach, winter squash, green vegetables, citrus fruits (Eggs have a small amount of zeaxanthin, too.)
  • Blueberries, blackberries, cranberries, cherries, strawberries, kiwifruit, plums, red grapes, red cabbage, eggplant (skin)
  • Apples, chocolate, cocoa, grapes, tea (black, oolong, or green), wine
  • Citrus fruit
  • Apples, broccoli, onions, tea

Functional Nutrition: A Quick Look at Key Phytonutrients (continued)

A Handful of Phytonutrients*

What They Appear to Do

Where They're Found (some food sources)

Flavonoids (continued) Proanthocyanidins

Resveratrol

Isothiocyanates

Sulphoraphane

Phenols

Caffeic acid, ferulic acid

Ellagic acid

Polyols

Sugar alcohols: lactitol, mannitol, sorbitol, xylitol

Phytoestrogens

Isoflavones: daidzein, genestein

Lignans Phytic acid

  • May contribute to maintaining urinary tract health and heart health
  • Bolsters antioxidant defenses in cells
  • May contribute to maintaining heart health
  • As an antioxidant, neutralizes free radicals that may damage cells
  • May aid in detoxification of undesirable compounds
  • Bolsters antioxidant defenses in cells
  • May bolster cellular antioxidant defenses
  • May contribute to maintaining healthy vision and heart health
  • Neutralize free radicals that may damage cells
  • Bolster antioxidant defenses in cells
  • May reduce risk of dental caries
  • May reduce menopause symptoms, such as hot flashes
  • May contribute to maintenance of bone health
  • May contribute to healthy brain function and immune function
  • May contribute to heart health and healthy immune function
  • May contribute to maintaining normal blood sugar levels and maintaining heart health
  • Neutralizes free radicals that may damage cells
  • Bolsters antioxidant defenses in cells
  • Apples, cinnamon, cocoa, cranberries, grapes, peanuts, strawberries, wine
  • Red grapes, red grape juice, red wine, peanuts
  • Cruciferous vegetables, such as bok choy, broccoli, broccoli sprouts, cabbage, cauliflower, collard greens, kale, turnips, turnip greens
  • Fruits, including apples, citrus, pears, some vegetables
  • Berries, red grapes, kiwifruit
  • Some chewing gums
  • Other food applications
  • Soybeans, soy-based foods
  • Flaxseed (not flaxseed oil unless hull remains), rye, wheat bran, oatmeal, barley, vegetables
  • Cereal grains, nuts, seeds

A Handful of Phytonutrients*

Prebiotics and Probiotics

Inulin, fructo-oligosaccharides, polydextrose

Lactobacilli, bifidobacteria

Soy Protein

Soy protein

Sulfides/Thiols

Allyl methyl trisulfide, diallyl sulfide

Dithiolthiones

What They Appear to Do

  • May improve gastrointestinal health
  • May improve calcium absorption
  • May improve gastrointestinal health and systemic immunity
  • May reduce risk for coronary heart disease (CHD)
  • May help maintain heart health
  • May help maintain a healthy immune system
  • May aid in detoxification of undesirable compounds
  • Contributes to maintenance of healthy immune function

Where They're Found (some food sources)

  • Whole grains, onions, some fruits, garlic, honey, leeks, fortified foods and beverages
  • Yogurt, other dairy and non-dairy applications
  • Soybeans, soy-based foods
  • Chives, garlic, onions, leeks, scallions
  • Cruciferous vegetables

Source: Adapted from: International Food Information Council Foundation, 2004.

Other phytonutrients are addressed elsewhere: fiber in chapter 6 and stanols and sterols in chapter 3. Animal-based foods also contain some functional substances, e.g., some fatty acids; see chapter 3.

No Dietary Reference Intakes exist for them yet.

Bottom line: Already there's overwhelming evidence for the health benefits of plant-based foods: fruits, vegetables, legumes (including soy), nuts, seeds, and grains, especially whole grains. Research shows that you lower the odds for some cancers, heart disease, and other health problems by eating more fruits, vegetables, and grains.

Count on a variety of foods to reap the benefits of the many phytonutrients from all kinds of plant-based foods. Supplements with just one or a few phytonutrients haven't been shown to be effective.

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