It seems that as we rediscover the wonder of fruits and vegetables—namely, that their health benefits go far beyond providing vitamins, trace minerals and dietary fiber—we're gradually broadening our vocabulary to talk much more technically about food than ever before. Now we're aware that the groceries Mom encouraged us to consume are not only nutritional powerhouses, but also the sources of disease-fighting "other" elements—phytochemicals. These include the more well-known lycopene, beta-carotene, and lutein, but also the more foreign anthocyanins, catechins, and resveratrol.
Since fruits and vegetables are the mainstay of a child's diet, we're naturally curious to learn more about how various phytochemicals may help promote optimal health as children grow. Which foods contain the most powerful phytochemicals, and therefore may pack the biggest punch against disease? As we continue to learn more, we may eventually find our friends talking flavonoids as readily as sports scores—especially if further research proves their importance in preserving long-term health.
What are Phytochemicals?
Phytochemicals are bioactive compounds found in plant foods. In addition to giving the plant its characteristic color, texture, flavor, and fragrance, phytochemicals are part of a plant's natural system for defense, repair, and reproduction. They are not "essential" in the diet in that they are not required for sustaining life. However, their functions in the body appear to be similar to those in plants—they confer important preventive and protective benefits for health.
Scientists have identified thousands of biologically active phytochemicals in fruits, vegetables, grains and nuts. All may not necessarily have health benefits, but many do, and all function in numerous biological processes that are extremely complex. Epidemiologic studies have suggested the possible associations of phytochemicals with health, and animal- and cell- culture approaches have begun to identify mechanistic explanations.
Three major categories of phytochemicals (classified by chemical structure) include carotenoids, polyphenols, and glucosinolates, although there are others. Health benefits have been associated with intake of specific phytochemicals within each category, and with intake of the group of phytochemicals as a whole. (See table, Phytochemicals: Classes and Functions.)
The benefits associated with phytochemicals have usually been linked with the intake of whole foods, most likely resulting from the interaction of the nutrients and phytochemicals that may have complementary and overlapping mechanisms of action. The concept of eating foods that complement each other nutritionally and interact to increase absorption and utilization by the body is called food synergy.1
Hypothesis testing with the isolated compound either in the laboratory or in human trials does not always yield anticipated results based on identified mechanisms. For instance, based on epidemiological, animal and cell culture studies, beta-carotene, the primary carotenoid found in many fruits and vegetables, was thought to be the bioactive component that reduced cancer risk, specifically lung cancer risk. Two randomized clinical trials were conducted with male smokers: the Alpha-Tocopherol, Beta-Carotene Prevention Trial (ATBC) in Finland and the Beta Carotene and Retinol Efficacy Trial (CARET) in the United States. Both trials produced the same unexpected results—lung cancer incidence was slightly higher in the supplementation group. However, dietary intake of beta-carotene at baseline was associated with a lower incidence of lung cancer in the ATBC trial. Thus, it may be that beta-carotene is a marker for intake of foods that contain other important substances that are preventive or that interact with beta-carotene for cancer prevention.2
The effectiveness of food synergy is also suggested by the relationships between fruit-and-vegetable-rich dietary patterns and certain health benefits. Several large-population studies have found that people who follow traditional Mediterranean or Asian diets and lifestyle are healthier and live longer than those who follow typical western practices. These healthier patterns include the consumption of large quantities of fruits, vegetables, and whole grains with only small amounts of fish and meat. In the Seven Countries Study, there was a lower incidence of coronary heart disease among populations originating from Greece and Southern Italy who were consuming traditional Mediterranean diets compared to populations consuming a western diet containing large amounts of red meat, processed meat, high-fat cheese and a lower intake of fruits and vegetables.3 Similarly, in a 25-year prospective study, centenarians living on the island of Okinawa had lower rates of heart disease and breast, colon, and prostate cancer as compared to both industrialized western countries and to younger Okinawans who adopted a westernized diet. The centenarians consumed a diet rich in rice, vegetables, fruit, soybeans, three or more servings of fatty fish per week and very little red meat.4
Observations in the ATTICA study add more evidence to the potential beneficial role of phytochemicals in the health benefits of certain dietary patterns. In the Attica region of Greece, the diet and blood samples of 3,042 participants with no evidence of cardiovascular disease were evaluated to determine the relationship between dietary patterns and total antioxidant activity (TAC). Results indicated that those who consumed a more traditional Mediterranean diet had higher TAC scores and lower oxidized LDL cholesterol levels. Additionally, a significant positive correlation of fruit and vegetable intake with TAC scores was observed.5
Similarly, results of an observational study revealed that the DASH diet, providing 9-10 servings of fruits and vegetables per day, provided greater amounts of flavonols, flavanones, ß-carotene, lycopene, lutein, and phytosterols compared to a control diet that included 3-5 servings. While the DASH diet is presumed to lower blood pressure because it provides optimal amounts of fiber, potassium, magnesium, and calcium, it is possible the positive effects of the diet are also attributable to phytochemicals.6
"Super Foods" to Watch For
Consuming a wide variety of colorful fruits and vegetables is the best way to reap their health benefits. Indeed, the world is full of foods that we may have never heard about and that may eventually prove to be tasty and healthful additions to our diets. Emerging science has focused attention on some of these new and exciting items and the food industry has been quick to produce samples for our dining experience. Although the research is far from conclusive, as far as determining health benefits, it is interesting to follow the emergence of exotic berries and tropical fruits that may eventually prove to be powerful disease-fighters or immune-boosters. For example, we have recently learned that pomegranates are high in antioxidants as well as vitamin C. Preliminary research suggested that pomegranate juice may help reduce risk for heart disease, prostate cancer and osteoarthritis.7 These same effects may not be seen with pomegranate extracts, however.8
Goji berries, also known as wolf berries, originate from Mongolia and the Tibet region of China. They have been important in Chinese medicine for thousands of years for enhancing the immune system, improving eyesight, protecting the liver and improving circulation. However, research is needed to confirm the potential benefits. The berries do contain zeaxanthin and appear to have high antioxidant activity.9 Sweet in taste, they can be eaten raw or consumed as juice.
The fruit of the acai palm, the acai berry is harvested in tropical Central and South America. It is traditionally used as a beverage and as a fresh fruit. In the past several years, it has become part of the functional-food industry due to its high content of vitamins and minerals, and high antioxidant activity owing to anthocyanins and other flavonoids. Some preliminary research has suggested anti-cancer and anti-inflammatory effects of acai, but more is clearly needed.10
A tropical evergreen tree, the mangosteen produces a fruit of a deep reddish-purple color with a sweet, citrus flavor. It is grown in Asian countries, and is found in the U.S. primarily canned, frozen or juiced. Fresh mangosteens are less available due to import concerns, although it is likely that in the future, they will be more available. The polyphenols in mangosteen are purported to be beneficial for the immune system.11
Popular in Brazil primarily in soft drinks, several studies have shown potential health benefits associated with the tropical guarana berry, including benefits to cognitive function.12 One study also showed those taking a mixture that included guarana for 45 days had an 11.2-pound weight loss compared to a 1-pound loss in the placebo group.(13)
Though research is still in the early stages, there may be health benefits associated with culinary use of spices as well. For instance, the essential oil of cinnamon may have anti-microbial activity,14 and supplementation with cinnamon has been associated with possible modest effects in lowering plasma glucose levels in type-2 diabetes.15 Curcumin, which imparts the yellow color in turmeric (an ingredient in curry powder) has been associated with antioxidant, anti-cancer and anti-inflammatory activity.16 Other spices that have shown phytochemical activity include cloves, ginger, red pepper, rosemary and anise.17
Amidst all the excitement over "new" healthy foods, traditional champions are still important. Brassica vegetables—broccoli, cauliflower, Brussels sprouts, cabbage, kale and bok choy—contain isothiocyanates that appear to have important roles for cancer prevention. Tomatoes contain lycopene, which may help fight prostate and possibly lung cancer. (This phytochemical is actually more available after cooking, so tomato paste and ketchup are good sources.) Most berries have high antioxidant activity as well, with blueberries standing out as one of the highest. Intake of berries has been associated with reduced risk of cardiovascular disease and some cancers. Similar to berries, red grapes (and red wine) contain anthocyanins, and intake has been associated with a reduced risk for cardiovascular disease.
Dark-green, leafy vegetables have also long had the reputation for healthfulness. We now know that in addition to being full of vitamins and minerals, they are rich in phytochemicals that have antioxidant activity. Many contain lutein and zeaxanthin, which are the macular pigments, and are important for prevention of macular degeneration and cataracts.
Mom's Diet Affects Baby
Data on consumption of fruits and vegetables indicate that overall, Americans are not meeting recommendations. In the 2005 Behavior Risk Factors Surveillance Survey (BRFSS), only 23.2% of adults reported consuming more than 5 servings a day.18 In the National Health and Nutrition Examination Survey conducted between 1999-2002, average total servings for adults were 5.2 and 4.5 for males and females, respectively.19 Furthermore, an analysis of trends since 1988 shows no changes in average intake of fruits and vegetables.20
The gap between recommendations and actual intake is not limited to adults. Consumption data indicates that a large percentage of children are far below recommendations, especially as they grow older. (See chart, Average Servings per Day Compared to Recommendations) A higher percentage of 2-5 year olds meet recommended levels, likely because they are still at home or in structured settings where there are fewer external influences and parents have more dietary control. As children grow older, external and environmental influences such as peers, media, school environment, and extra-curricular activities can have an impact on intake of fruits and vegetables.
Studies have shown that early exposure to fruits and vegetables as well as to foods that are high in fat and sugar shapes preferences for these foods. Additionally, where children readily accept sweet and salty foods, they often need to learn the taste preference for vegetables. Food ‘neophobia' and pickiness develop around the second year of life until about 6 years of age. However, it has been shown that, with repeated exposure, resistance can be broken down and dislikes can be transformed such that the avoided food may even become desired. Research has shown that it may take offering a particular food up to 20 times before it will be accepted by the child.21
Parental food choices also shape food acceptance. In one study, individuals identified themselves as family food preparers and completed questionnaires about their eating habits and the eating habits of family members. Results showed that the fruit-and-vegetable consumption of the family food preparer predicted the fruit-and-vegetable consumption of the spouse, children and adolescents in the family. Additionally, the more meals the child shared with the family food preparer, the stronger the relationship of the family food preparer's fruit-and-vegetable intake with the child's.22 Other studies have also shown that consumption is enhanced when fruits and vegetables are consumed as part of family meals, illustrating the influence of parental modeling of behavior.23 The recommendation to serve a new food with a favorite food and offer it in an encouraging, non-pressuring manner will help to increase acceptance for a new fruit or vegetable. Additionally, serving meals in an emotionally positive environment will create a positive association with the foods that are being offered.
Studies have documented that although fruit-and-vegetable intake tends to increase in adulthood, it also tends to track into adulthood, and adolescent fruit and vegetable intake appears to predict adult intake.24 Consumption of fruits and vegetables also seems to be influenced, in part, by habit, underscoring the importance of making fruits and vegetables consistently available at meals and snacks.25 To increase consumption by older children and adolescents who are making food choices more independently, it may be necessary to go a step beyond availability and prepare fruits and vegetables so they are ready to eat for snacks and meals on the go.26
Increasingly, scientific evidence is supporting the health benefits of consuming plant foods that are rich in phytochemicals, particularly fruits and vegetables. Accordingly, in 2005, recommendations for intake were increased in the Dietary Guidelines for Americans. Leading public health agencies including the American Heart Association, American Cancer Society and American Diabetes Association also provide recommendations—by adulthood, most encourage intake of up to 13 servings per day, depending on age and activity level. Average intakes of adults and children did not meet previous guidelines, and trends in intake had not changed substantially since before 1988. Therefore, the 5 A Day Program was initiated in 1991. Although intake has remained the same, the good news is that since then, 70% of adults indicate they are aware of the 5 A Day message, and 40% said they should be eating 5 or more servings per day.(27)
In light of the new, higher recommendations and the mounting evidence for increasing intake, the Fruits & Veggies—More Matters™ brand replaced the 5 to 9 A Day Program and the 5 A Day The Color Way Program in March, 2007. This new initiative is a public-private partnership between the CDC (the lead federal health authority for the program) and the Produce for Better Health Foundation. Formative research indicated that the message "it all adds up" is more motivating than a quantitative message, which seemed unachievable, especially when it included the more recent, higher recommendations. Fruits and Veggies—More Matters™ focuses on small, achievable steps that get consumers to eat more fruits and vegetables over time.
Acquiring a taste for fruits and vegetables is important for lifelong health. Children learn by being involved, and it's been shown that kids who help take part in planting, harvesting, purchasing and preparing vegetables generally consume more of these foods. Making fruits and vegetables available, providing variety and repeatedly exposing children to them in a positive and encouraging environment are key to acceptance and consumption. Fruits & Veggies—More Matters™ (www.fruitsandveggiesmorematters.org) provides actionable steps for including more fruits and vegetables in the family's diet and practical tips through an interactive forum for increasing children's consumption.
Kathy Hoy, EdD, RD, CDE, is Nutrition Research Manager at the Produce for Better Health Foundation, which is the private arm of the public/private partnership for implementing Fruits & Veggies—More Matters™ with the CDC. Dr. Hoy develops and coordinates PBH research focused on understanding behavioral factors associated with consumption and evaluating effectiveness of Fruits & Veggies—More Matters™ activities.