To the average American, vegetables continue to fall low on the list of food preferences, contributing to poor intake. Yet, vegetables rank among the most important food groups for optimizing and maintaining health, largely because they are the chief carriers of antioxidants. Oxidative stress is unarguably a root problem in the pathology of some of our most common chronic diseases and conditions including cancer, diabetes, cardiovascular disease, liver and kidney diseases, and dementia. Therefore, it is crucial to provide the body with ample supplies of phytochemicals with antioxidant activity by encouraging a greater consumption of vegetables.
Striving for more phytochemicals does not mean we must seek out and fill our refrigerators with rare vegetables that possess superfood-status. Even the most commonly consumed vegetables are rich in phytonutrients. In a comparative study, analyzing the total phenolic content of common vegetables, broccoli won the prize, followed by spinach, yellow onion, red pepper, carrot, cabbage, potato, lettuce, celery, and cucumber. When the total antioxidant activity was evaluated, red pepper came out at the top, followed by broccoli, carrot, spinach, cabbage, yellow onion, celery, potato, lettuce, and cucumber. This study also included an in vitro analysis using HepG(2) human liver cancer cells of the antiproliferative activities of the various phenolics in common vegetables to determine which would be most helpful for playing a potential role in cancer prevention. The antiproliferative activity of the phenolics in spinach was the highest, followed by cabbage, red pepper, onion, and broccoli. These studies show that even the most commonly available vegetables can impart vital health benefits.
The Shanghai Women's Health Study and Shanghai Men's Health Study sought to evaluate the relationship between dietary patterns, food groups, and liver cancer risk in two cohort studies of 132,837 Chinese women and men. Results showed that a vegetable‐based diet (compared to a fruit- and meat-based diet) was inversely associated with liver cancer. More specifically, high intakes of celery, mushrooms, allium vegetables, composite vegetables (including asparagus and lettuce), and legumes were associated with reduced liver cancer risk. As expected, the vegetable‐based dietary pattern was associated with higher intakes of phytochemicals with antioxidant activities and antioxidant vitamins including vitamins A, C, and E. Specific anticarcinogenic actions of these antioxidants include modulation of phase I and II enzymes, stimulation of the immune system, and inhibition of mutagenesis and DNA adducts.
Many of our commonly consumed vegetables are members of the cruciferous vegetable family, including broccoli, cauliflower, turnip greens, cabbage and Brussels sprouts. This family of vegetables contains unique phytochemicals called glucosinolates, which are hydrolyzed to isothiocyanates and modulate several biochemical pathways associated with the development of bladder cancer. In in vitro studies, isothiocyanates inhibit bladder cancer cell lines, arrest the cell cycle, and induce apoptosis. Further, isothiocyanates target the adaptive stress response, phase I/II enzyme modulation, pro-growth, pro-survival, pro-inflammatory signaling, angiogenesis, and even epigenetic modulation, all of which help maintain an environment that is not conducive to the growth of cancer cells.
The phytochemicals found in vegetables may also help protect against the recurrence of breast cancer in women also taking conventional therapy. In an analysis from the Women's Healthy Eating and Living Study, the vegetable intake of 3,080 breast cancer survivors was assessed and compared to the hazard ratio of breast cancer recurrence. Those with the highest intake of vegetables had the lowest hazard ratio for recurrence, indicating a protective effect from the vegetables. In a similar study evaluating the effects of cruciferous vegetable intake on the breast cancer treatment-related symptoms among breast cancer survivors, higher cruciferous vegetable intake was associated with lower odds of experiencing symptoms such as hot flashes, night sweats, vaginal dryness, vaginal discharge, joint problems, fatigue, hair thinning/loss, and memory problems.
The phytochemicals in vegetable are powerful agents that function to fight against oxidative stress and protect the body from damaging processes that contribute to disease development and progression. Even the most common vegetables found in grocery stores can supply rich quantities of health-promoting phytochemicals. Perhaps, the greatest challenge is simply implementing this foundational health principle. Despite being familiar advice, it bears repeating again and again – eat your vegetables!