| Analysis of Food-based Antioxidants |
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Bananas have very little in the way of antioxidants, but are useful in the diet to provide dietary fibre and potassium (400 mg/100 g). However, dried fruits and nuts are better potassium sources. | |
Similarly, melons are generally poor sources of antioxidants, with the exception of cantaloupes which have 2 mg/100 g beta carotene. |
| Inactivity of food-based antioxidants |
Clinical and epidemiological trials | |||
| Evidence is slowly accumulating from human intervention and prospective studies to prove areas of inactivity for so-called therapeutic antioxidants - the bad list. However, some antioxidants are degraded rapidly and may, during the process of absorption, give rise to active metabolites. One example of this is quercetin, whose glucuronidated, sulphated and methylated derivatives were active in in vitro cell cultures. Reference: S. Tribolo et al., Aterosclerosis in press Very few trials of this sort have been conducted and therefore the absence of compounds from this list merely means that they have not yet been tested. A second line of investigation suggests that lipophilic antioxidants such as ascorbyl palmitate may perturb membrane bilayers to the detriment of cells. (M. Olsher and P. L-G. Chong, Anal. Biochem., 382 1-8, 2008.) which may tie up with the adverse effects of lipophilic antioxidants observed in recent clinical trials. |
| Antioxidant (type) | Location | Type of trial | Negative result |
| Lycopene (carotenoid) | Serum | Prospective study | Increased concentration of serum lycopene not helpful against prostate cancer |
| beta carotene (carotenoid) | Serum | Prospective study | High serum beta carotene levels associated with increased risk of prostate cancer |
| Reference: U. Peters et al., Cancer Epidemiol. Biomarkers Prevention, 16, 962-968, 2007 | |||
| beta carotene vitamin A vitamin E | Supplements | Evidence from 68 randomised trials (over 200,000 participants) | All three antioxidant supplements may actually increase mortality. This meta-study result has been criticised by the Head of Linus Pauling Institute (OSU). He says that major trials, reported in reputable journals have been ignored, pointing up the problem of impartial choice when meta studies are collated. |
| Reference: G. Bjelakovic et al., J.A.M.A., 297 (8), 843-857, 2007. | |||
| Lycopene (carotenoid) | Tomatoes, watermelon | Human intervention | No change to antioxidant capacity or cholesterol status of middle-aged adults |
| Reference: J.K. Collins, et al., Nutr. J. 3, (15), 2004. [Open-access] | |||
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