Superfruit Nutrition

By Marie Spano, M.S., R.D., Contributing Editor

Mentions of superfruits often conjure images of exotic fruits full of antioxidants, fruits that bring us a step closer to the fountain of youth and healthy living every time we consume their juicy pulp. But even though superfruits come with an array of healthy compounds, the category name is somewhat of a misnomer.

The superfruit category

First and foremost, there is no regulatory or scientific definition of a superfruit," notes Jeffrey Blumberg, Ph.D., professor, Friedman School of Nutrition Science and Policy, and director, Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston.

However, the word superfruit" is often used to describe novel fruits that are great sources of nutrients, antioxidants and anticipated health benefits. Often, the word itself is used to define more-exotic fruits, such as goji berry and açaí. As studies confirm health benefits of more common fruit, like blueberries or cranberries, they too gain the title superfruit." But, the lack of a uniform definition means that the term superfruit" is applied liberally in marketing materials for a number of products. And, often, well hear about a superfruits ORAC score as a descriptive statistic to back its placement within this category of foods. Yet this score is also misleading.

Quantifying antioxidants

Companies might use a combination of total antioxidant capacity (TAC) scores and the names of various antioxidants to tout a fruits benefits. These TAC scores measure the cumulative capacity of food components to scavenge free radicals. They are often used to compare plant-based foods with one another and relate total antioxidant intake in epidemiological studies with oxidative stress-related diseases (Journal of Nutrition, 2003; 133:2,812-2,819). Antioxidant capacity assays use either single electron transfer (ET) or hydrogen atom transfer (HAT) to reduce radicals and measure total antioxidant capacity (Journal of Agriculture and Food Chemistry, 2006; 54:1,151-1,157). Some of these tests include:

              ORACoxygen radical absorbance capacity (HAT);

              FRAPferric reducing-antioxidant power (ET);

              TEACTrolox equivalent antioxidant capacity using ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) (ET);

              TRAPtotal radical-trapping antioxidant parameter (HAT);

              DPPH2,2′-diphenyl-1-picrylhydrazyl free radical scavenging potential (ET).

The type of test chosen depends on the potential antioxidants tested and the physiological pH of the sample. Each test provides an estimate of total antioxidant capacity; however, no single test can provide a complete picture of the antioxidant capacity of a piece of fruit (Journal of Agriculture and Food Chemistry, 2006; 54:1,151-1,157). In fact, using different tests on one piece of fruit may result in different measured outcomes of TAC, highlighting a glaring shortcoming of these tests.

Total antioxidant capacity, regardless of the test used, shouldnt influence a consumers choice of fruit, since TAC tests do not take into account the absorption and utilization of various antioxidants in the human body. There are several factors that can determine the absorption and bioactivity of antioxidants, such as the form of the food (liquid or solid matrix) and the types of other foods consumed at the same time, our gut flora and genetic profile, as well as our health status and age," notes Blumberg. Therefore, though these assays can be used as research tools for different purposesfor example, testing methods to extend the shelf life of a food productthey mean nothing with regard to human health."

A joint study between USDA Human Nutrition Research Center on Aging, the USDA Western Human Nutrition Research Center and the University of Maine highlighted the differences in antioxidant absorption among fruits. In this study, volunteers ate varying amounts of cherries, dried plums, kiwifruit, red grapes, strawberries and wild blueberries, and scientists measured their postprandial spike in antioxidant capacity as measured by ORAC. Kiwifruit outperformed the other fruits for increasing blood antioxidant levels, likely due to their high vitamin C content (vitamin C is well-absorbed by the body), despite the fact that other fruits had higher levels of specific antioxidant compounds, including anthocyanins, proanthocyanidins and flavonols. Another interesting finding was that consumption of blueberries and cherries resulted in an increase in the subjects fat-soluble antioxidant capacity, even though these berries do not contain large quantities of such antioxidants (Journal of the American College of Nutrition, 2007; 26:170-181).

Investigating health benefits

Numerous studies indicate that a diet rich in fruits and vegetables is associated with lower rates of cardiovascular disease and some types of cancer (Annals of Internal Medicine, 2001; 134:1,1061,114; Gastroenterology, 2002; 123:985991; Nutrition and Cancer, 2000; 38:2329). And, although scientists have identified some of the specific antioxidant compounds and their health benefits, there is a lot we still do not know about the antioxidants in our food, how much we should ideally consume to improve specific health parameters and what groups of people will benefit from specific compounds.

Thus far, a plethora of rat studies show that blueberry extract offers neuroprotection and may slow age-related declines in memory (Neurobiology of Aging, 2006; 27:344-350; Nutritional Neuroscience, 2005; 8:111-120; Pharmaceutical Research, 2005; 52:457-462; Nutritional Neuroscience, 2000; 3:383-397). In vivo research shows that blueberries may hold some promise for inhibiting the growth of colon, prostate, breast and oral cancer cell lines (Journal of Agricultural and Food Chemistry, 2006; 54:9,329-9,339).

Another fruit that has been in the marketplace in various forms for decades, cranberry, comes with potential health attributes as well, including preventing urinary tract infections (UTI) in women who suffer from recurring UTIs (Journal of Clinical Gastroenterology, 2010; 44:S61-S62; Drugs, 2009; 69:775-807) and possibly helping prevent dental caries and periodontal disease (Journal of the Canadian Dental Association, 2010; 76:a130).

There are fewer clinical trials on newer exotic fruits like pomegranate and açaí, but we know that each of these fruits has a specific nutrition profile. Pomegranates are an excellent source of vitamin C and contain 11 grams of fiber, 5 grams of protein and an array of antioxidants. Açaí is unique because it contains essential fatty acids, fiber and antioxidants. Dried plums, although theyve been around for decades, have been renamed and packaged to appeal to consumers and food manufacturers alike. Dried plums are high in potassium and boron, and contain phenolic compounds that may aid in laxation.

In reality, all fruits are superfruits, because each one has a different set of nutrients and antioxidants and, therefore, potential health benefits. There are thousands of dietary antioxidants, but we dont know which ones are the most important or what the optimal intakes are for promoting good health and preventing disease. Therefore, consumers should eat a wide variety of fruits and antioxidant-rich foods with every meal and chew food well, since chewing food can help improve the absorption of antioxidants and other nutrients.

Food manufacturers should consider an array of fruits for incorporation into their functional foods and beverages to deliver added nutritional value and a variety of flavors to stimulate the taste buds. In addition, manufacturers would benefit from designing foods that use processing techniques that preserve the fiber and antioxidants in food.

Marie Spano, M.S., R.D., CSCS, CSSD, is a nutrition communications expert and food industry consultant. Marie writes for popular press magazines and trade publications, has given cooking demos on NBC, ABC, FOX and CBS affiliates and helps companies formulate healthy products. For more information, visit mariespano.com.