Free radicals and disease

It makes sense to ensure that your diet is high in antioxidants. High doses of B-carotene and vitamin C, fresh fruit and veg are your best bet – ‘coloured’ vegetables such as green leafy ones, beetroot, carrots and sweetcorn are particularly high in B-carotene.

If you’re in regular training, your body undergoes numerous adaptations to be able to come up with the increased energy demanded. One such adaptation is an increase in muscle mass, together with an enhanced capacity for muscular aerobic metabolism. The process of aerobic metabolism involves fuel being combusted in the presence of oxygen (oxidation for short) to release energy which can then be trapped by ATP. The series of charged chemical reactions involved in oxidation takes place in the ‘powerhouses’ of the cells, the mitochondria. Mitochondria are self-contained structures within cells, surrounded by their own membrane.
The link between free radicals and disease
Now, the ability to harness oxygen’s energy is a sophisticated technique that took many aeons of evolution to achieve. But it’s not a risk-free process. During the series of oxidation reactions, a small percentage of highly ‘excited’ oxygen leaks out. This hyperactive customer is one of a mob of zappy, highenergy molecules that are called free radicals. Free radicals are so keen to get on and react with other substances that they start off destructive chain reactions. Free radical damage has been implicated as a factor in heart disease, cancer, rheumatoid arthritis, and even the process of ageing.

It’s thought that a significant part of the damage is related to effects on cell membranes, structures which are highly vulnerable to free radical disruption. Experimental work has shown that the effects can be as drastic as cells being completely torn apart, so that their contents leak into the bloodstream.

But it’s not all doom and gloom. As part of our evolution, we’ve also come up with ways of disarming these highly reactive molecules, calming them down and converting them into harmless entities. The substances involved are called anti-oxidants and a number of these lie in wait in the cell membranes. Some are enzymes, others will be more familiar to you as vitamins – vitamins E, C and A (as its Bcarotene incarnation). The mineral selenium also probably plays a role. Together, these free-rad busters do a pretty good job most of the time at minimising the number of free radicals that escape unchallenged into the cell.

Athletes have a higher free radical load
However, under circumstances where more oxidation is taking place than usual, there will be more free radicals to deal with. And if you’re doing a lot of physical exercise, this means you. As an active athlete, your body is carrying out higher levels of oxidation to meet the extra energy requirement. This means that the coping strategies for minimising the negative effects of free radicals will be taxed – sometimes beyond their limits. When this happens, large-scale muscle structures can be damaged; muscles can end up being overly contracted, sore, and less efficient at using energy. Red blood cells can become ‘leaky’, malformed and easily broken, which may lead to anaemia.

All is not lost, since there are things you can do to compensate for your higher free rad load. As we’ve mentioned before in PP, it makes sense to ensure that your diet is high in antioxidants. For high doses of Bcarotene and vitamin C, fresh fruit and veg are your best bet – ‘coloured’ vegetables such as green leafy ones, beetroot, carrots and sweetcorn are particularly high in B-carotene.

Effect of type of dietary fat
Another potential dietary strategy was examined recently in the Journal of Sports Medicine and Physical Fitness (Huertas et al, ‘Dietary polyunsaturated fatty acids and peroxidative risks in sport practice. Alternatives’, J Sport Med & Phys Fitness, June 1994, vol 34(2), pplO1108). This hinges around the way in which free radicals damage cell membranes. Membranes are fluid structures composed mainly of phospholipids (specially adapted fatty acids) and proteins. It’s been discovered that a free radical can react with the fatty acid components of the membrane, converting them in turn into reactive molecules which can carry on a destructive chain reaction. This process is known as lipid peroxidation. To carry out this reaction, an ‘unsaturated’ chemical bond is needed. Fatty acids fall into three categories saturated (no unsaturated bonds), monounsaturated (just one unsaturated bond), and polyunsaturated (two or more unsaturated bonds).

Research has established that free radicals are far more likely to react with phospholipids based on polyun saturated fatty acids. And the good news is that you can have some influence on the makeup of your membranes through what you eat.

Monos for your membranes
The proportion of saturated fatty acids in cell membranes has been found to be pretty much constant. But the ratio of polyunsaturated:monounsaturated has been discovered to be influenced by diet. Basically, the more polyunsaturates you eat, the more will show up in your membranes, and the same for monounsaturates. It’s been shown both in laboratory animals and in human subjects that after a short adaptation period, the fatty acid composition of the membranes is representative of the dietary intake.

So, it would be predicted that a diet rich in monounsaturates would lead to membranes which were more resistant to lipid peroxidation. Researchers have confirmed this in animal experiments: free-radical derivatives were found to be higher in membranes of rats fed corn oil (a polyunsaturate) than those fed olive oil (a monounsaturate) (Life Sciences 1992, vol 50, pp2 1 1 1 -8).

Olive oil fights peroxidation
Taking this a step further, the same researchers attempted to reproduce the higher oxidative stresswhich results from increased physical exercise. In another animal experiment, rats were fed adriamycin (ADR), an antibiotic which initiates lipid peroxidation. When ADR was admininstered in the last three days of a two-month period of treatment with selected dietary fat sources, there was a statistically significant increase in free radical derivatives in the membranes of all experimental groups. However, free rad derivatives in the group fed olive oil were significantly lower than those in the animals fed corn oil.

The authors concluded that diets with olive oil as the unique fat source are able to produce membranes whose features allow them to be more resistant to lipid peroxidation even if the overall cell metabolism is increased (Life Sciences, 1992, ibid). This outcome has not been confirmed for human subjects, but the circumstantial evidence is fairly strong. It has been shown that free radical production increases during intensive sporting practice (Europeam Journal of pplied Physiology, volS6 pp313-6). It’s also been demonstrated that people’ s cell membranes reflect their dietary fat intake.

What does this mean in practical terms? To change the ratio of polyunsaturates to monounsaturates in your diet, the most significant thing you can do is to use olive oil in preference to a polyunsaturated oil (such as sunflower, corn, blended vegetable oils). It’ s also possible to buy dairy-type spreads based on olive oil. Avocados are rich in monounsaturates, as are some nuts, including hazelnuts, cashews, and almonds .

Janet Pidcock

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