Problematising antioxidants

cloudspyder (59)in #steemstem • 8 years ago

We have seen the kind of errors made by those in the nutrition-ism movement as they strive to justify their more obscure and technical claims. What's more fun is to take our new understanding and apply it to one of the key claims of the nutrition-ism movement, and indeed to a fairly widespread belief in general. The claim that you should eat more antioxidants.

As we now know, there are lots of ways of deciding whether the totality of research evidence for a given claim stacks up and it's rare that one single piece of information clinches it. In the case of a claim about food, for example, there are all kinds of different things we might look for. Whether it is theoretically plausible, whether it is backed by what we know from observing diets and health, whether it is supported by intervention trials where we give one group, one diet and another group of different one, and whether those trials measured real-world outcomes, like "death" or a surrogate outcome such as blood test which is only hypothetically related to a disease.

My aim here is by no means to suggest that antioxidants are entirely irrelevant to health. In think you find it a bit more complicated. I intend as they say to problematise the prevailing nutritionist view on antioxidants which currently lags about twenty years behind research evidence.

From an entirely theoretical perspective, the idea that antioxidants are beneficial for health is an attractive one. When I still attended my medical science subject not so long ago, I used to read biochemistry textbooks. This book is filled with complex interlocking flow charts of how chemicals which is what made us of, move through our body. Its show how different enzymes break down food into constituent molecular elements, how these are absorbed, how they are reassembled into new larger molecules that our body needs to build muscles, retina, nerves, bones, hairs, membrane, mucus, and everything else that you're made of. How the various forms of fat broken down and resembled into new form of fat or how different molecule such as sugar, fat, alcohol are broken down gradually, step by step to release energy. How that energy is transported and how the incidental products from that process are used or bolted onto something else to be transported in the blood, and the ditched at the kidneys or metabolized down into further constituents, or turned into something useful elsewhere and so on. This is one of the great miracle of life, and it is endlessly, beautifully, intricately fascinating.

Looking at these enormous, overwhelming interlocking webs, it's hard not to be struck by the versatility of the human body, and how it can perform acts of near alchemy from so many different starting points. It would be very easy to pick one of the elements of these vest interlocking systems and become fixated on the idea that it is uniquely important. Perhaps it appears a lot on the diagram or perhaps rarely and seems to serve a uniquely important function in one key place. It would be easy to assume that if there was more of it around, then that function would be performed with greater efficiency.

But as with all enormous interlocking systems - like the society for example - an intervention in one place can have quite unexpected consequences. There are feedback mechanisms, compensatory mechanisms. Rates of change in one localized area can be limited by quite unexpected factors that are entirely remote from what you are altering, and excess of one thing in one place can distort the usual pathways and flows, to give counter intuitive results.

Theory underlying the view that antioxidants are good for you is the free radical theory of ageing. Free radicals are highly chemically reactive, as are many things in the body. Often this reactivity is put to very good use. For example, if you have an infection, and there are some harmful bacteria in your body, then a phagocytic cell from your immune system might come along, identify the bacteria as unwelcome, build a strong wall around as many of them as it can find, and blast them with destructive free radicals. Free radicals are basically like bleach, and this process is a lot like pouring bleach down the toilet. Once again, the human body is smarter than anybody you know.

But free radicals in the wrong places can damage the desirable components of cells. They can damage the lining of your arteries and they can damage DNA. A damaged DNA leads to ageing or cancer, and so on. For this reason, it has been suggested that free radicals are responsible for ageing and various diseases. This is a theory, and it may not be correct.

Antioxidants are compounds which can - and do - "mop up" these free radicals, by reacting with them. If you look at the vast, interlocking flow chart diagrams of how all the molecules in your body are metabolized from one form to the next, you can see this is happening all over the shop.

The theory that antioxidants are protective is separate to - but builds upon - the free radical theory of disease. If free radicals are dangerous, the argument goes and antioxidants on the big diagrams are involved in neutralizing them, then eating more antioxidants should be good for you, and reverse or slow ageing, and prevent disease.

There are a number of problems with this theory. Firstly, who says free radicals are always bad? If you're going to reason just from theory, and from diagrams, then you can hook all kinds of things together and make it seem as if you're talking sense. As I said, free radicals are vital for your body to kill off bacteria in phagocytic immune-cells. So should you set yourself un in business and market an antioxidant-free diet for people with bacterial infections?

Secondly, just because antioxidants are involved in doing something good, why should eating more of them necessarily make that process more efficient? I know it makes sense superficially, but to do a lot of things and that's what's really interesting about science. Sometimes the result aren't quite what you might expect. Perhaps an excess of antioxidants is simply excreted or turned into something else. Perhaps it just sits there doing nothing, because it's not needed. After all, half a tank of petrol will get you across town just as easily as a full tank. Or Perhaps if you have an unusually enormous of antioxidant lying around in your body doing nothing, it doesn't just do nothing. Perhaps it does something actively harmful. That would be turn-up for the books, wouldn't it?

There were a couple of other reasons why the antioxidant theory seemed like a good idea twenty years ago. Firstly, if you take a static picture of society, people who eats a lots of fresh fruit and vegetables tend to live longer, and have less cancer and heart disease. And there are lots of antioxidants in fruit and vegetables. Although there are lots of other things in them too and you might rightly assume, lots of other healthy things about the lives of people who eat lots of healthy fresh fruit and vegetables, like their posh jobs, moderate alcohol intake, etc.

Similarly when you take a snapshot picture of the people who take antioxidant supplement pills, you will often find that they are healthier or live longer. But again although nutritionist are keen to ignore this fact, these are simply surveys of people who have already chosen to take vitamin pills. These are people who are more likely to care about their health, and are different from the everyday population. Far beyond their vitamin pill intake, they may take more exercise, have more social supports, smoke less, drink less alcohol, etc...

But the early evidence in favor of antioxidants was genuinely promising, and went beyond mere observational data on nutrition and health. There were also some very seductive blood results. In 1981 Richard Peto, one of the most famous epidemiologist in the world, who shares the credit for discovering that smoking causes 95% of lung cancer, published a major paper. He reviewed a number of studies which apparently showed a positive relationship between having a lot of B-carotene onboard. B-carotene is an antioxidant available in the diet that help reduce cancer risk.

This evidence included case-control studies where people with various cancers were compared against people without cancer and it was found that the cancer free subjects had higher plasma carotene. There are also prospective cohort studies in which people were classified by their plasma carotene level at the beginning of the study, before any of them had cancer, and then followed up for many years. These studies showed twice as much lung cancer in the group with the lowest plasma carotene, compared with those with the highest level. It looked as if having more of these antioxidants might be a very good thing.

Similar studies showed that higher plasma levels of antioxidant vitamin E were related to lower levels of heart disease. It was suggested that vitamin E status explained much of the variations in levels of ischemic heart disease between different countries in Europe, which could not be explained by differences in plasma cholesterol or blood pressure.