Allium Foods: Mystical Functional Foods for Health Promotion
There is little doubt that nutrition and health are intimately intertwined. For generations, people have believed that foods can do more than merely provide energy and nutrients for growth and development and thus contribute to overall health and disease prevention. Beliefs about the medicinal properties of foods have been highlighted in a number of the early writings. Hippocrates is frequently quoted to proclaim “Let food be thy medicine and medicine be thy food.” Today, statements about the ability of foods and food components to reduce disease risks or enhance the quality of life are relatively commonplace and continue to captivate our lives.
Garlic and other allium foods (onions, leeks, chives, etc.) are commonly consumed foods which are often revered for their potential medicinal properties. This reverence has been promoted in recent years, especially for garlic, because of the emergence of data revealing that in addition to antimicrobial properties these foods may reduce human illnesses including that related to heart disease and cancer. The ability of garlic and its constituents to assist in maintaining normal immune-competence and possibly improve mental function suggests it, and possibly other allium foods, may have widespread health implications1, 2. Unfortunately, while the interrelationship between garlic intake and health are intriguing, there remain a dearth of well-controlled clinical investigations with allium foods and the data that exist is often inconsistent. The current series of articles point to the potential benefits of garlic, and onions, in several health related conditions. The articles also provide evidence that it would be unwise, and inappropriate, to assume that all individuals will respond identically, if at all.
Many reasons may explain why a food, such as garlic, might be inconsistently related to a health outcome3. Dietary exposures, specific targets modified by the components in the food, and interactions with other nutrients in the diet or by the genomics of the consumer are likely key variables and fundamental to determining the direction or magnitude of the overall response. Foremost among these is the variation in the amount of the active agent(s) that arrives at the target site. Unfortunately, reliable tools for estimating intakes/exposures are unavailable, along with relative poor databases about the amount of these foods that is added to prepared foods. Questions about the use or non-use, or frequency are often so imprecise that it is difficult to draw strong conclusions. Likewise, our ability to assess the use of supplements remains in its infancy and contributes to uncertainty about the range of intakes and thus biological consequences. The use of standardized test to evaluate natural and commercial garlic preparations as suggested by Gonzales et al4 offers interesting possibilities for better defining true garlic exposures.
While there are problems in evaluating intake, there are even greater challenges in evaluating the content of specific bioactive constituents occurring in garlic that are being consumed. Undeniably there is more to garlic than the odor associated sulfur constituents. Variation in these other constituents including arginine rich proteins, fructooligosaccharides, and flavonoids, as well as the sulfur constituents, likely contribute to the variability in response. Growing conditions can influence the composition of many plants/herbs and thus likely accounts for some of the variation in response to garlic grown and processed throughout the world. Several years ago Lawson and Gardner5 highlighted the wide variation in the types of sulfur compounds that can occur in various garlic preparations and their stability. Comparison of these variation preparations is sometimes similar to comparing apples and oranges in that they are within the same class of foods but can be exceeding different in the bioactive constituents they provide. Again, standardization methods may help shed light on what intakes are needed to bring about a desired response. Dr. Galeone (in this issue) concluded that onions were more beneficial in retarding myocardial infarction than garlic. Thus, it cannot be assumed that all allium foods are identical. Greater attention to the merits of individual foods for specific purposes needs, and deserves, greater attention.
Defining the molecular target for garlic and its active components is another important challenge. Based on epidemiological, preclinical and intervention data, multiple pathways appear to be influenced by the allyl sulfur compounds arising from garlic once eaten as a natural food or a commercially available preparation. The article by Reinhard (this publication) provides compelling evidence that garlic reduced blood pressure, but on those with baseline pressures greater than 140 mmHg. Thus, an insult (including excess calories, bacteria, viruses, etc.) might be needed to achieve benefits from the enhanced intake of allium foods. Understanding the cellular process that has been changed to account for the reduction in blood pressure is of paramount importance. One must ask if the response is specific to some type of insult or genotype that makes the individual vulnerable and thus determines the benefits from exaggerated garlic intake. It is important to note that this study suggests that the response to garlic may be equivalent to what is classically observed with drugs. Thus, opportunities exist for using it as a dietary component for optimizing health. Additionally the combination of agents (drugs and nutrients) may offer exciting opportunities for promoting health while minimizing adverse events and associated complications.
While there is a wealth of preclinical evidence linking allium foods intake, particularly garlic, with cancer risk and tumor behavior, the amount of clinical evidence is far less plentiful or compelling. The article by Kim and Kwon (in this series) highlights the challenges associated with unraveling the true relationship between garlic intake and cancer and how to convey the most appropriate message to consumers. While several cellular changes including oxidative stress, DNA repair, decreased cell division, apoptosis and immunocompetence may account for a response, the actual molecular event accounting for the decrease in cancer burden deserves far more attention1, 6. Again, it should be noted that individuality in response to garlic is evident throughout the cancer research literature. This variation may be due to the ability to absorb, metabolize or secrete the active agents in garlic. It is most logical that genetic and epigenetic variation among individuals contributes to the response that is observed3, 7, 8.
While exciting information exist about the health benefit of allium foods, and garlic in particular, the dearth of clinical information make strong recommendations challenging. Nevertheless, the information in this series of articles highlights their potential health benefits, while recognizing not all individuals will share the benefits equally. Since the ill-consequences are generally limited to halitosis, and remedial methods exist, there are few reasons to limit these foods in the diet. Maybe the old saying can be modified to “a clove” a day will keep the doctor away”.
- Butt MS et al. Crit Rev Food Sci Nutr. 2009;49(6):538-51.
- Haider S et al. J Med Food. 2008;11(4):675-9.
- Davis CD & Milner JA. Acta Pharmacol Sin. 2007;28(9):1262-73.
- Gonzalez RE et al. 2009 Oct 14. [Epub ahead of print]
- Lawson LD & Gardner CD. J Agric Food Chem. 2005;53(16):6254-61.
- Milner JA. J Nutr. 2006;136(3 Suppl):827S-831S.
- Milner JA. Cancer Lett. 2008;269(2):189-98.
- Dashwood RH & Ho E. Semin Cancer Biol. 2007;17(5):363-9.