Last Updated on August 4, 2021 by Max
It has long been noted that the regular consumption of fruits, vegetables, and whole grains is correlated with a low incidence of chronic diseases such as cancer, cardiovascular disease, autoimmune diseases, etc. Scientists began to attribute these health benefits of plant foods to various biologically active substances isolated from different parts of plants. However, the assumption that isolated individual antioxidants or phytochemicals can replace the intake of plant foods has proven to be erroneous, if not harmful. The results of clinical trials are not consistent as to the beneficial effects of the dietary supplements and cannot explain the observed health advantages of diets rich in fruits, vegetables, and whole grains. Dietary supplements in clean form may not work in the same way as the ingredients of the whole food and, in addition to having fewer useful effects, may also be potentially dangerous.
Let’s take a look at the results of some reported clinical trials. Also note that the vast majority of such studies are sponsored by companies who have a business interest, and, in the case of negative results, are usually not published.
Clinical trials showed the harmful effects of popular food supplements on human health.
β-Carotene is an excellent dietary antioxidant found in carrots and some other vegetables and was proven to protect from lung cancer based on several studies. In a study by Pisani, P. et al. (1986) current smokers who consumed carrots more than once a week, showed a threefold low risk of developing lung cancer compared with those who did not eat them.
However, in clinical trials, β-carotene supplementation did not show any beneficial effect on smokers in respect to lung cancer (Omenn GS, et al. 1996). It was a well-organized randomized, double-blind, placebo-controlled trial involving more than 18,314 smokers, former smokers, and workers exposed to asbestos. The study aimed at the effects of daily ingests of 30 mg of β-carotene and 25,000 IU of vitamin A on the incidence of lung cancer, compared with placebo. The experiment was stopped 21 months earlier than planned, because contrary to expectations, there has been a significant increase in the lung cancer rate and total mortality rate in the supplemented group.
Vitamins C, A, and E, zinc, and niacin showed no significant effects on mortality rates from all causes in a Chinese study involving 29,584 adults (Blot WJ. et al. 1993).
The GISSI-Prevenzione trial couldn’t reveal any beneficial effect of Vitamin E on the endpoints of myocardial infarction, stroke, or death for the patients who had had a myocardial infarction (Lancet. 1999).
Vitamin E is known as the reproduction vitamin and selenium often enhances the biological activity of vitamin E. Therefore, an extensive study has been undertaken on the effectiveness of these dietary supplements in preventing prostate cancer. Selenium and Vitamin E Cancer Prevention Trial (SELECT) involving 35,533 Americans, studied the potential of selenium (200 µg/day) and vitamin E (400 IU/day) to prevent prostate cancer. The results of this trial showed an increased risk of prostate cancer in the vitamin E group, and an increased risk of type 2 diabetes – in the selenium group ( Lippman SM, et al. 2009). The clinical trial was stopped because of ethical and safety concerns. Three years later following the first report of SELECT in 2009, the rate of prostate cancer in the vitamin E supplementation group raised to 17% higher (P = 0.008) compared with the placebo group. These results certainly show that vitamin E supplementation significantly increases the risk of prostate cancer among healthy men (Klein EA. et al. 2011).
Unlike refined food additives, the whole extracts of fruits, vegetables, and whole grains exhibit strong antioxidant and health-protecting activity. So, the whole phytochemical extract from apples showed strong antitumor activity in tumor cell cultures and animal models inhibiting mammary cancer in rats. Here, the whole apple extracts hindered mammary cancer in a rat model in a dose-dependent manner at doses comparable to human consumption of 1, 3, and 6 apples a day (Liu RH, et al. 2005).
A study by Cohen JH et al, (2000) showed that eating more than 28 servings of vegetables, particularly cruciferous vegetables, per week is associated with a reduced risk of prostate cancer by 35% compared with an intake of less than14 servings per week.
The additive and synergistic effects of phytochemicals in plant foods have been suggested to be in charge of their antioxidant and anticancer potentials. This partially explains why no single antioxidant can substitute the mixture of phytochemicals in fruits and vegetables to achieve the observed health benefits.
Milenkovic et al. (2011) reported interesting results on a human nutrigenomics study. They tested how orange juice and hesperidin, a purified citric phytochemical, affect the expression of genes in healthy people after the four-week consumption. They found that both orange juice and hesperidin intake significantly affected the expression of human genes. Drinking of orange juice changed the expression of 3422 genes, intake of hesperidin induced the expression of 1819 genes, and 1582 genes were in common in both groups. This study also supported the importance of whole food instead of a single phytochemical.
Each bioactive compound in fruits, vegetables, and whole grains has its distinctive profile with its specific molecular size, polarity, solubility, bioavailability, metabolic pathways, and excretion. However, unlike pure supplements, the effect of phytochemicals in whole foods harmonized with hundreds of other compounds, which determine the distribution and concentrations of each phytochemical in different organs, tissues, and cells. Therefore, the health benefits of whole foods cannot be achieved by dietary additives in the form of tablets or pills. People should get antioxidants or phytochemicals from a balanced diet with a wide variety of fruits, vegetables, whole grains, not from dietary supplements. Furthermore, eating whole foods is safer and is not likely to result in the consumption of toxic quantities compared with tablets or capsules. Fruits and vegetables eaten in the recommended amounts (9–13 servings of fruits and vegetables per day) are safe.
However, I am not advocating to avoid any kind of additives. But you need to understand that the pure phytochemicals of plants often do not possess the full spectrum of health benefits of whole foods, and hence, whenever you have a choice, always give preference to whole healthy food. And sometimes, contrary to expectations, the supplements even can harm your health as in the case with vitamin E. Therefore, one must always be careful with the choice of additives and especially with the duration of their use.
- Pisani, P., Berrino, F., Macaluso, M., Pastorino, U., Crosignani, P. and Baldasseroni, A. (1986) Carrots, Green Vegetables and Lung Cancer: A Case-Control Study. International Journal of Epidemiology, 15, 463-468.
- Omenn GS, Goodman GE, Thomquist MD, Barnes J, Cullen MR. Effects of a combination of β-carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996;334:1150–5.
- Blot WJ, Li JY, Taylor PR, Guo W, Dawsey S, Wang GQ, Yang CS, Zheng SF, Gail M, Li GY. Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence, and disease-specific mortality in the general population. J Natl Cancer Inst. 1993;85:1483–92.
- GISSI-Prevenzione Investigators Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet. 1999;354:447–55.
- Lippman SM, Klein EA, Goodman PJ, Lucia MS, Thompson IM, Ford LG, Parnes HL, Minasian LM, Gaziano JM, Hartline JA, et al. Effects of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301:39–51.
- Klein EA, Thompson IM, Jr, Tangen CM, Crowley JJ, Lucia MS, Goodman PJ, Minasian LM, Ford LG, Parnes HL, Gaziano JM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011;306:1549–56.
- Liu RH, Liu J, Chen B. Apples prevent mammary tumors in rats. J Agric Food Chem. 2005;53:2341–3.
- Milenkovic D, Deval C, Dubray C, Mazur A, Morand C. Hesperidin displays relevant role in the nutrigenomic effect of orange juice on blood leukocytes in human volunteers: a randomized controlled cross-over study. PLoS ONE. 2011;6:e26669.
- Cohen JH, Kristal AR, Stanford JL. Fruit and vegetable intakes and prostate cancer risk. J Natl Cancer Inst. 2000; 92:61–8