Inside the Crossfire

a combination of primary nutrient qualities -- including significant contents of dietary fiber, vitamin C, phenolics and carotenoids -- are signatures of true superfruits relatively few fruits actually have such signatures to qualify as super the four proposed superfruit criteria relate to four FDA-approved health claims for plant foods and soluble dietary fiber lowering risk of some cancers and cardiovascular disease high content of soluble (fermentable) dietary fiber may be the most important superfruit signature consumers can identify superfruits by edible peels, skins and seeds (dietary fiber) combined with color richness (vitamin C, phenolics, carotenoids)

We assume superfruits have exceptional nutrient and antioxidant qualities, making them special sources for developing superior natural health products.

But shouldn't the definition of superfruit rely on objective, scientific nutritional qualities not typically emphasized on marketing materials and press releases?

Without objective criteria, many fruits are promoted by manufacturers as “super”, yet may have thin scientific evidence for being exceptional in any way related to nutrient or phytochemical content. A few fruits in fact were added to the superfruit category only after achieving marketing success.

Wolfberry (goji, Lycium barbarum L.) and seabuckthorn (seaberry, Hippophae rhamnoides L.) stand out as unusually nutrient-dense fruits (1), giving them distinction with four qualifying “signatures” as superfruits. Each has high contents of the following nutrient features

1. phenolics (water-soluble polyphenols with laboratory evidence for antioxidant properties)
2. carotenoids (lipid-soluble antioxidants)
3. vitamin C (a universal antioxidant essential for human health)
4. soluble dietary fiber, a macronutrient fermented as a prebiotic substrate in the lower digestive tract, yielding short-chain fatty acids with numerous potential health benefits

A fruit having all four of these qualities would fall within four different FDA-approved health claims for plant foods and soluble dietary fiber lowering risk of some cancers and cardiovascular disease (2), distinguishing it truly with significant dietary qualities and potential for reducing disease risk.

Establishing nutrient signatures may help differentiate superfruit candidates and, with objective criteria, disqualify others not having substantial nutritional attributes. To summarize, four nutrient criteria of interest are

1)   phenolics, the largest and most common class of antioxidant phytochemicals in the plant kingdom, notable as red, blue, violet, purple and black pigments demonstrating promise as therapeutic agents according to preliminary research (3). They are water-soluble, distributing readily by bulk flow throughout most organ water compartments, including inside cells where they may also have transmitter or signal enabling properties (4). Human evidence for health benefits of phenolics, however, remains unproven. Phenolics may be associated with a related FDA health claim for fruits and vegetables: 21 CFR 101.78 for lowered risk against some types of cancer (2).

2)   carotenoids, a smaller but significant class of orange and yellow antioxidant pigments, among which beta-carotene and beta-cryptoxanthin are provitamin A sources (5). A working theory exists that carotenoids furnish higher antioxidant quality per molecule than phenolics (5), are stored in lipid compartments including membranes of nuclei and other cellular organelles, and so may be a proximate antioxidant defense at the cell level in concert with phenolics. Carotenoids may also be associated with a related FDA health claim for fruits and vegetables: 21 CFR 101.78 for lowered risk against some types of cancer (2).

3)   vitamin C (ascorbic acid), the most abundant, water-soluble antioxidant essential to human health (6). When particularly high in content, small amounts of a superfruit containing rich vitamin C would furnish a significant % of the dietary reference intake (DRI). Vitamin C may also be associated with a related FDA health claim for fruits and vegetables:21 CFR 101.78 for lowered risk against some types of cancer (2).

4)   soluble dietary fiber, common as a plant energy store in the form of polysaccharides such as beta-glucans, pectins and oligosaccharides. Upon fermentation by colonic bacteria, fiber acts as a prebiotic yielding short-chain fatty acids (e.g., butyrate, acetate, valerate) which may confer numerous potential health benefits (7,8) including reduction of blood cholesterol levels and lowered cancer risk. Fermentable fibers are approved for limited health claims by the FDA for food products containing beta-glucans from oats, barley or psyllium (2). Specified FDA health claims are 21 CFR 101.76, 21 CFR 101.77, 21 CFR 101.78 and 21 CFR 101.81 for lowered risks against coronary heart disease (reductions in blood cholesterol levels) and reduced risk against some types of cancer (2).

5)   should a fruit combine all four differentiating nutrient qualities, it would have promising value as a compounded (water- and lipid-soluble) antioxidant source plus essential nutrients (vitamins, fiber) implicated with lower disease risks.

Shown in Table 1 are four fruits mentioned in recent industry reports as ingredients for superfruit products. These fruits also qualify for superfruit status because basic research indicates significant progress for providing evidence of anti-disease activity.

The table illustrates differences in superfruit nutrient criteria but is exclusive neither for fruits to be included at this stage nor for superfruit signatures. Other fruits have favorable combination of nutrients, phytochemicals and preliminary research evidence for anti-disease effects to justify them as possible superfruits.

For example, fruits having 3-4 of qualifying nutrient characteristics include kiwifruit (Actinidia deliciosa), papaya (Carica papaya), Indian gooseberry (Phyllanthus emblica) and Rubus berries such as red and black raspberries and blackberries, all notable for combined richness of phenolics, dietary fiber and vitamin C. Carotenoids may be present in the pulp, such as for papaya, or in the many seeds of kiwifruit and Rubus berries (9).

This list in Table 1, therefore, serves only as a way of introducing and considering objective signatures for superfruit status, then comparing superfruit candidates using these criteria.

Superfruits with 4 distinct nutrient and antioxidant signatures – guava (Psidium guajava, left) and mango (Mangifera indica). See Table 1. Sizes not to scale.

Signature nutrients and preliminary medical research

Each fruit's principal nutrient quality is given with evidence against disease models from recent medical research. More extensive references are available from the author.

1. Aronia (Aronia melanocarpa). One of the richest natural sources of tannins, proanthocyanidins and anthocyanins. Evidence in laboratory models for lowering high blood cholesterol (10).

2. Guava (Psidium guajava). Enriched in all four signature nutrients of Table 1. Anti-cancer and anti-inflammatory evidence (11).

3. Mango (Mangifera indica). A multiple nutrient fruit distinct by its orange-yellow (carotenoid) pigmented rind and pulp. Rich in all four signatures of Table 1. Anti-inflammation and anti-cancer activity (12).

4. Yumberry (red bayberry; Myrica rubra). Moderate in nutrient content but high especially in the polyphenol, ellagic acid. Presence of numerous other antioxidant phytochemicals (13).

To provide a grading system for comparing scientific knowledge about plant foods, Medline Plus (14) gives the following used in Table 1:

A: significant scientific evidence in favor

B: good scientific evidence in favor

C: moderate or uncertain

D: good scientific evidence against

F: significant scientific evidence against

Table 1. Fruits with qualifying “signature” grades for superfruit status

Fruit	Phenolics	Carotenoids	Vitamin C	Dietary fiber	Superfruit Grade Average
Aronia	A	D	C	C	C
Guava	B	A	A	A	A
Mango	B	A	A	A	A
Yumberry	B	D	C	D	C

Nutrient profiles for the fruits were reviewed on Nutritiondata.com (USDA), World's Healthiest Foods (EHSA Research, Salem, Oregon, http://whfoods.com) or as available on Medline (US National Library of Medicine). Phytochemical data were assessed from published literature for each fruit (see PubMed abstracts).

Conclusion and FDA Health Claim Context

Four nutrient criteria are highlighted to recognize two superfruits not usually included in discussions about this category: guava and mango, each having significant content of phenolics, carotenoids, vitamin C and dietary fiber.  Although both guava and mango are among the world's most consumed  fruits, they are not often discussed as superfruits, yet they join wolfberry (goji) and seabuckthorn  containing all four signatures each in high content.

Such combined nutrient qualities in each of these four fruits are uncommon among plant foods, providing examples of nutrient- and antioxidant-rich plants having nutritional criteria that indeed make them exceptional. Retaining such nutritional qualities or reconstituting nutrients to restore original contents is a desirable goal in manufacturing superior-quality superfruit products.

Among 9 fruits most commercialized as superfruits, signature grades are summarized in Table 2.

Possibly the most general distinguishing characteristic of superfruits as a class are not antioxidant phytochemicals or vitamins but high content of soluble dietary fiber, usually in the form of polysaccharides (8) used as an energy store in fruit pulp for growth of the plant. Upon fermentation in the colon, ingested polysaccharides yield short-chain fatty acids having an array of physiological effects associated with health benefits (7,8).

Some of these fiber effects are related to four approved health claims for lowering risk of cancer and cardiovascular disorders (Reference 2; FDA claims 21 CFR 101.76, 21 CFR 101.77, 21 CFR 101.78 and 21 CFR 101.81). Other nutrient characteristics with FDA health claims (2) that may provide further differentiation of superfruits include

1. high calcium content (21 CFR 101.72)
2. low total fat content (21 CFR 101.73)
3. low sodium content (21 CFR 101.74)
4. low saturated fat content (21 CFR 101.75) (a feature disqualifying seabuckthorn which has high pulp content of palmitic acid, a saturated fat)
5. high phytosterol content (21 CFR 101.83)
6. whole food quality (docket 1999P-2209)
7. high potassium content (docket 2000Q-1582)

Each of the four superfruits presented above – wolfberry, seabuckthorn, guava and mango – has most or all of these seven nutrient qualities plus the four signatures featured in this article (Tables 1, 2).

Table 2. Summary of phytochemical and nutrient grades for well-commercialized superfruits