Fruit and vegetable consumption rates still fall below recommended levels in most world societies and dietary supplementation is one way to gain lost nutrients. Without regular consumption of naturally-occurring plant-based compounds such as antioxidant polyphenolics, carotenoids, fiber, vitamins, minerals, and other compounds, we risk an increased susceptibility to inflammation and chronic diseases that progress as we grow older. What makes fruits and vegetables “good for you” is the subject of intense research, and encouraging outcomes have resulted from the efforts. An emerging field in the area of health promotion from a plant-based diet is the symbiotic relationship between humans and beneficial bacteria in our gastrointestinal tract. These bacteria are capable of creating new bioactive metabolites from the foods we eat. For example, many plant-based polyphenolics from our diet are absorbed soon after ingestion, but others are acted upon by intestinal bacteria and add to the diversity of biologically-active compounds circulating in our blood stream. Once absorbed, these compounds are also metabolized by our liver to create more new compounds that have shown positive health benefits. A diet rich in fruits and vegetables will have higher concentrations and a greater diversity of circulating metabolites that can help with faster recovery from stress or exercise and in the long-run will help delay onset of chronic diseases.
Fruits and vegetables have different phytochemical compositions that impact their role on human health. For example, mango, raspberry, and green tea all contain different types of tannin polyphenolics (Figure 1 and 2), compounds that are not absorbed directly from our diet. With the help of beneficial intestinal bacteria a diversity of metabolites are created that offer strong anti-inflammatory activity and contribute to our overall health and well-being.
Unfortunately, some people may not possess the type or number of beneficial intestinal bacteria to adequately digest tannins, and therefore an imbalance or dysbiosis exists. Dysbiosis may result from inflammatory bowel diseases that are estimated to impact over 1 million people annually at a cost of over $4 billion/yr to treat (1). Another cause is obesity and other non-diagnosed bowel inflammations estimated to cost over $200 billion/yr in lost work productivity, over-the-counter medications, hospital visits, and medical claims according to the Centers of Disease Control and Prevention. However, intestinal dysbiosis may be improved with consistent, daily consumption of plant-based phytochemicals. Our study with humans consuming 400 grams of tannin-rich mangos every day for 10 days (2) revealed an ability to increase absorption of metabolites produced by intestinal bacteria (Figure 3). Our follow-up study compared lean (BMI <25) and obese (BMI >30) individuals consuming 400 grams of mango daily and found that obese subjects were unable to initially metabolize and absorb tannins effectively, but after 42-days of daily consumption were able to increase metabolite production (Figure 4). By comparison, bacterial metabolites were initially high for lean individuals and yet more than doubled after 42-days of mango consumption.
In contrast to fruits, vegetable crops with high concentrations of natural pigments are gaining popularity as a food colorant, antioxidant, and dietary supplement with red beet betalains, purple sweet potato anthocyanins, and black carrot anthocyanins among the most widely used by the food industry. Whereas anthocyanins are a type of polyphenolic, betalains (or betacyanins) are a derivative of an aromatic indole yet both express strong red and pink colors to foods. Although intestinal bacteria can metabolize betalains, these compounds are absorbed directly from our food and metabolized by the liver (Figure 5) into betanin-glucuronide and betanidin sulfate (3). As a result, betalains can occur in our stool and urine leading some to believe it is blood due to its bright red color. In one study, up to 0.9% of red beet betalains consumed were excreted in urine over a 12-hour period (4). Beets also contain inorganic nitrates and nitrites that are chemically reduced to nitric oxide in our body and act as a vasodialator. Since betalains are antioxidants, their presence during digestion can aid in nitric oxide production (5) and provide additional benefits to consumption.
Although we often consume fruits and vegetables with their flavor in mind, their contribution to health and our body’s ability to produce bioactive compounds is an added benefit. However, it is clear that most people do not consume sufficient amounts of plant-based foods and current research indicates systemic health benefits are lost as a result. With adequate and consistent intake of foods rich in bioactive phytochemicals, along with maintaining healthy intestinal bacteria, our ability to derive health benefits from these foods may increase over time.
- Rubin, D.T., Modey, R., DFavid, K.L., Wang, C.-C. 2014. Real-world Assessment of Therapy Changes, Suboptimal Treatment and Associated Costs in Patients With Ulcerative Colitis or Crohn’s Disease. Alimentary Pharmacology & Therapeutics, 39, 1143-1155.
- Barnes, R.C., Krenek, K.A., Talcott, S.U., Talcott, S.T. 2016. Urinary Metabolites from Mango (Mangifera indica L. cv. Keitt) Galloyl Derivatives and In Vitro Hydrolysis of Gallotannins in Physiological Conditions. Molecular Nutrition & Food Research, 60, 542-550.
- Roemmelt, A.T., Franckenberg, S., Steuer, A.E., Kraemer, T. 2014. Purple discoloration of the colon found during autopsy: Identification of betanin, its aglycone and metabolites by liquid chromatography–high-resolution mass spectrometry. Forensic Science International, 240, e1-e6.
- Kanner, J.; Harel, S.; Granit, R. 2001. Betalains A New Class of Dietary Cationized Antioxidants. Journal of Agricultural and Food Chemistry, 49, 5178–5185.
- Hord, N. G., Tang, Y., Bryan, N. S., 2009. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. American Journal of Clinical Nutrition, 90, 1-10.