Millions of people throughout the world don't get enough to eat. Not surprisingly, their health suffers. We need food for growing, repairing ourselves, keeping all our body systems ticking over properly, and reproducing. We also need food for activity – even sitting thinking uses energy, and physical work, of course, uses a lot more. Without adequate food intake, all these things suffer.
But here in the developed world, very few of us go to bed hungry on a regular basis. We have plenty to eat, and generally live longer than our counterparts in the developing world. Of course, we do get ill, but the immediate cause isn't usually lack of food.
Why, then, is there currently such an obsession with trying to improve our health and performance with specific dietary components? If we are already healthy by all normal measures, why do we want to be healthier – how could we tell, and what benefits might it bring us? And, more importantly, what makes us believe that a particular supplement will do the trick for us?
The evidence that food supplements improve health is patchy to say the least. Yes, vitamin C is important for health – without it we would get scurvy, and there is some evidence that moderate doses allow us to recover from colds more quickly. But that's a long way from proving that massive doses can prevent colds, as is sometimes claimed.
And there is, relatively, a lot of research on vitamin C, including the 'gold standard' of clinical trials. In many cases the trials just haven't been done and even when they have, there's no justification for mentally extending the conclusions to areas the trials were never designed to cover. Take, for example, the 'bioactive' probiotic drinks and yoghurts available in a supermarket near you.
Laboratory studies and some animal tests have shown that these drinks may indeed improve colon function and digestive health, if the microbes they contain survive long enough to get to the colon, and if they remain there for long enough to have an effect. And we don't really know if this happens - many researchers believe that you would have to drink as much as 5 litres a day of the probiotic to see any effect!
There's no evidence that fish oil can help you pass exams
Also in the news recently has been the story from Durham of giving children studying for their GCSEs a daily dose of fish oil. Everybody knows that fish oil is good for you, so what's the problem? Well, there's some evidence that fish oil can boost your immune system, but none at all that it can help you to pass exams.
There's an opportunity here for a proper trial: give some students fish oil, and to a matched group give a placebo, and see which group scores the better. But this isn't being done, so we will never know whether the fish oil helped or hindered. And that's the point about many of the claims being made: in many cases, the most you can say is that they will probably do you no harm. Personally, I'll go for a balanced diet every time.
The fish oil files – The Guardian's Ben Goldacre on the Durham trials
Probiotics research published by the Food Standards Agency
The Vitamin C Myth National Public Radio's Morning Edition audio report on the gap between the claims for Vitamin C and the evidence
Human Nutrition – a Health Perspective by Mary E. Barasi
Understanding Human Nutrition – Open University short course perfect if you are interested in your own and your family’s diet, or if you are involved in the nutrition and health of others