N° 66 | April 2012

Fruits, Vegetables, and Health: A Scientific Overview, 2011

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Research related to fruits and vegetables (FV) over the past five years has expanded and added to earlier evidence supporting a positive association between FV intake and human health. Several encouraging trends are noteworthy, including a greater number of investigations being conducted in countries beyond America and Europe to include non-Western groups, demonstrating potential benefits of FV intake across populations. There is also an important shift toward recognizing the value of the composite of nutrients and components in FV, rather than attributing observed outcomes to isolated or single compounds. Several investigators acknowledged that mixtures and interactions in foods are difficult to mimic with isolated compounds, and that native FV are often more effective.

Variety important

A few new studies have suggested that the variety of FV consumed might be as important as the quantity. Although national guidelines, health professionals, and organizations advocate variety based on nutrient composition, the emphasis in most scientific studies has historically been placed upon quantity.

Provocative new work in humans has built upon animal data suggesting that consuming FV may improve cognitive performance in both healthy individuals and those with neurodegenerative conditions. Promising studies of the effect of FV on disease-related processes, including inflammation and oxidation, advance our understanding of these conditions and others. There is also support for a positive effect of FV on pulmonary function, particularly in CO PD, and the potential of FV to attenuate the adverse effects of environmental pollutants on lung health.

Positive impact on body weight

A number of new studies have demonstrated that body-weight regulation and related conditions, including diabetes and hypertension, might be positively impacted by FV consumption, an important and timely focus given the need for more effective strategies to promote weight loss. There are promising but inconsistent data related to the effects of FV on bone mass in humans. However, there is still much work to be done to determine the independent effect of FV on health and to expand upon preliminary findings that hint at positive effects of FV intake on arthritis and eye health.

In spite of these findings, a number of large prospective trials have been published and the results have not consistently supported the outcomes of earlier observational and case-control studies, particularly related to cancer, and to a lesser extent, cardiovascular disease. While the impressive numbers of subjects in these studies are important, methodological limitations are still present. Many large trials rely upon self-administered Food Frequency Questionnaires to determine FV intake at periodic intervals, often two or more years apart. Although most assessment tools have been validated, it is possible that there is systematic under- or over-reporting of food groups. Infrequent assessment also increases the chance of missing dietary shifts between measurement periods.

Inconsistent findings related to FV and cancer, cardiovascular disease, and bone health have also been reported in meta-analyses and recent pooled reports. However, as acknowledged by the authors of many of these, there is a significant degree of heterogeneity between studies examining FV intake and human health. A number of assumptions are made when data are pooled to reconcile the great variety of approaches to dietary assessment, inconsistent stratification and classification of FV intake and quantities, diverse outcome measures, highly variable duration periods, and different exposures to FV.

Further work required to answer questions

It is important to be cautious in interpreting the outcomes of recent reports and to recognize the need for further work using well designed, tightly controlled and standardized approaches across multiple conditions and populations. There are numerous plausible mechanisms by which FV might be protective and many unanswered questions regarding the potential importance of variety, quantity, duration, and nature of FV effects on disease-related processes. Thus, the study of FV must remain an active area of research to confirm the true effect of FV intake on human health and build upon the promising data currently available.

Data for the review were collected from database searches of PubMed and Medline for peer-reviewed articles published between July 1, 2006, and January 5, 2011. Key search terms included full and truncated forms of the words fruit(s), vegetable(s), fruits and vegetables, and (in alphabetical order) age, aging, Alzheimer’s, arthritis, asthma, bone, birth defects, body weight, brain, cardiovascular disease, cataracts, chronic obstructive pulmonary disease, cognitive, dermatological, diabetes, diverticulosis, eye, gastrointestinal, hypertension, inflammation, life span, longevity, neurodegenerative, obesity, oxidation, skin, weight.

The full report can be found at:
http://www.pbhfoundation.org/pdfs/about/res/pbh_res/PBH_Health_Benefit_Review.pdf

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