Energy essential for living is derived from foods by the action of digestive oxidants, which also simultaneously generate harmful free radicals, which can, in turn, be neutralised by antioxidants. Therefore, it is important to maintain the balance, either by reducing the body's exposure to unnecessary oxidative stress, or by increasing the antioxidant intake, or both. Normally, there are adequate amounts of antioxidants present in the foods we eat, but under adverse conditions (poor quality diet, limited food supply, environmental pollution, poor health) the balance can be upset. Certain foods contain substantial quantities of potentially therapeutic antioxidants to help sustain human health and well-being. go to >>>> total antioxidant capacity There are alternative theories of the antioxidant mechanism which invoke hormetic principles, (low concentrations - therapeutic ; high concentrations toxic),and utilise the concept of exposure to minor stress in order to strenghten (immunise) the body to face more major assaults. It is by no means clear how the biochemical pathways are triggered, but it is proven through epidemiological trials that diets rich in fruits, vegetables, nuts and grains - i.e. the plant foods, protect against degenerative diseases and extent the lifespan. However, other essential minor nutrients e.g. iron, selenium are better absorbed from animal products. Pehaps the most apposite addage is "moderation in all things".

What are antioxidants?

Antioxidants are compounds of many different chemical forms, lumped together because they all have the property of counteracting the effects of highly reactive, harmful free radicals formed as the result of essential oxidation reactions performed on food to release energy for our use. Subdivisions can be formed from those that :-
a) prevent the formation of free radicals, such as transferrin, SOD, carotenoids
b) neutralise those that are formed, thus inhibiting chain-breaking processes, such as, the vitamins A, E and C
c) repair the damage caused by free radicals, such as the DNA repair enzymes, e.g. transferase.
Natural antioxidants are synthesised by plants and are present in the foods we eat, as opposed to those synthetic antioxidants that are either added to food to extend its shelf-life (e.g. BHT), or prepared by extraction from plant sources to be taken as supplements in concentrated form.

What do they do for the plant?

Plants use the chemicals we call antioxidants in many different ways, e.g. in defence against being eaten by browsing animals and insects (some are bitter to the taste), to protect themselves from infection by viruses and bacteria (some have antibacterial and antiviral properties), to attract insects for pollination and animals and birds for seed dispersion (some are brightly coloured). Many of the polyphenols are intermediates and end up (after further chain extension to condensed tannins) in the supporting fibres giving the plant rigidity.

What do they do for us?

Plants containing high concentrations of antioxidants that are eaten in moderation have been associated in epidemiological studies with human well-being, while excessive consumption has been associated with toxic reactions. Using supplements has not been generally proven to replace the use of food-based antioxidants. Some supplements are known to increase mortality. Recent work suggests that not all the antioxidants present in foods are capable of being absorbed from the digestive tract into the bloodstream (i.e. are bioavailable), from whence they can be delivered to the various organs where they are required. So, even the efficacy of food-based antioxidants is still being tested.

Caution

Evidence that an antioxidant or even a class of antioxidants are effective in preventing, containing or curing a disease is difficult to validate. Nutritional authorities are cautious until more definitive studies have been performed. In the meantime, trends indicated by peer reviewed research are reported here.
go to >>>> therapies

What's new at this site?

It is an independent location, where the almost-daily release of information to the media, and in the scientific press, on the pros and cons of natural antioxidants can be presented together with the original scientific reference. It might therefore become a reliable place to find an unbiased, factual report, leaving the visitor to decide whether or not the information is relevant to their needs.

Measurement

Until a method is adopted as definitive, there are data in the literature which cannot be easily correlated. The best that can be done is to use a batch for comparison and attempt to calculate conversion factors from one batch to another. However, because the concentrations of natural compounds in plant foods are affected by several variables (climate, variety, soil condition, post harvest storage, etc.), the batch to batch values can only be approximate, even when the same analytical methods are used. Go to >>>> chemical analysis. A recent contribution has been the development of a Relative Antioxidant Capacity Index (RACI), which takes a statistical average of around 7 methods. Go to >>>> Relative antioxidant capacity.

What of the future?

Determine the function of individual antioxidants.
The total antioxidant extract from a food can be separated by chromatography and/or electrophoresis and the isolated fractions collected and submitted to biochemical assay to determine their properties. Some key antioxidants e.g. quercetin (Go to >>>> major sources of named antioxidants) have been studied to determine their antioxidant capacity and clinical role. As more compounds are analysed, the picture of their therapeutic utilisation will become clear.

The analyst's paradox

Evidence is growing that single pure phytochemical compounds, known to have in vitro antioxidant properties, do not contribute to the total antioxidant capacity when used in human intervention studies, since they are poorly absorbed from the gut, or they are absorbed but are either, not active or, they decompose to secondary products which may or may not have antioxidant properties.
The first hurdle in determining the human benefit from a chosen compound is to measure its absorption efficiency. Examples have been posted on the bioavailability page which illustrate the paradox. One study suggests that some compounds can be absorbed, e.g., (the target anthocyanin, cyanidin-3-glucoside, and the carotenoids, beta-cryptoxanthin and zeaxanthin) were absorbed from blood orange juice.
The second hurdle is to determine whether the absorbed compound(s) contribute to the total antioxidant capacity. Another study on lycopene and beta-carotene administered in tomato puree, found that they were absorbed satisfactorily from the food, but did not contribute to the total plasma antioxidant capacity.
So, a third hurdle is postulated. The flavanoids in flavanoid-rich foods are poorly absorbed, so the significant increase in the total plasma antioxidant capacity recorded at the time of ingestion must be attributed to other factors, like the stimulation of the production of endogenous cellular antioxidants such as uric acid and cellular enzymes, e.g. super oxide dismutase.
And finally, recent work by A.P. Gunning et al., FASEB, doi: 10.1096/fj.08-106617. confirms by spectroscopic analysis that bioactive fragments of pectin bind to the recombinant form of galectin 3 inhibiting its role in cancer progression and metastasis, thus, for the first time, providing a biochemical hypothesis for the epidemiological evidence that diets rich in fruits and vegetables are effective against degenerative human diseases.
Diets rich in pectin are also rich in vitamin and flavanoid antioxidants. Hence the mechanistic dilemma: Do flavanoid antioxidants neutralise free radicals, reduce oxidative stress, and reduce the spread of cancer, or do modified pectins bind to and inhibit proteins such as galectin-3 with the same end effect? A bit of both, no doubt. Prof. Vic Morris, the senior author on the above paper, advises us to hedge our bets by continuing with the five-a-day fruit and vegetable, high fibre, high pectin, high antioxidant food regime.