You aren’t what you eat: diet and health

Diet and health: I doubt whether there is any field in science where there is so much opportunity and incentive for medical charlatans to forge for themselves a lucrative career. Why? I can identify three key reasons. First, we all eat, so there’s a potentially huge market. Second, it’s fairly obvious that what we eat, and how much of it, has a bearing on our general well-being. Third, scientists don’t know all that much about the relationship between diet and health – certainly, far less than you’d expect them to considering the importance of this subject.

Let’s begin by exploring this third theme. Medical ignorance is an open door to bogus health ‘experts’, who operate outside the rules of the scientific and medical establishment, but tend to like to subserve some of the establishment respectability in peddling their advice or wares. Some of these charlatans even go to the extent of calling themselves Dr, when their ‘qualification’ is a PhD obtained by correspondence course from a non-accredited university – this is only a very small step up from buying a doctorate off the internet without any study at all.

Now I’m not claiming that science has a monopoly on all ‘truth’ or even all useful medical information. Science can and does get things wrong; there exist good doctors and bad ones. But the scientific system has at its core a solid way of verifying the accuracy of information, by experimental test and then peer review of all published work. In medicine it’s important to know whether treatments work, and the only way this can be done is by verification by trial and/or experiment. We all have a tendency to fool ourselves; the scientific method saves us from this.

Many ‘experts’ on diet and health operate outside the scientific system, yet they make claims about their therapies or advice that are couched in scientific terms. These often sound plausible enough to non-experts, but very few of these claims are backed up by proper evidence and a lot of them are essentially untestable. I’m not suggesting that these diet experts are all corrupt and evil – they likely, in many cases, genuinely believe what they are saying, and want to help people. Yet what they do is extremely unethical and undermines evidence-based medicine.

Does this all sound a bit rant-like? Let me explain what I mean by this. Essentially, they are duping people, whether they recognize this or not, because they are using science talk to establish credibility, masquerading as part of the medical establishment, while not paying the price of the entry ticket – experimental evidence subjected to peer review. By spouting untested claims and unverifiable theories, they are muddying the waters for genuine medics and confusing consumers.   

Why is it we know so little about the relationship between diet and health? It’s largely because it’s so hard to investigate properly. The consequences—for good or ill—of diet typically take years to show themselves, and we all eat such a wide variety of foods that it’s hard to pin down the precise effects of just one component. Besides, if you were asked to describe exactly what you’d eaten and drunk in the last week, let alone the last month, you’d have real problems. Experiments on people are limited in their scope: would you like to be shut up in a laboratory for six months while your diet was precisely controlled and its effects on your bodily functions assessed? Nor would I.

A further problem is that of confounding. People who take care with their diet and eat ‘healthy’ foods are also more likely to do healthy things like go jogging, playing tennis and maintain good family relationships. If you look at the usage of fast food restaurants, people of low socioeconomic status are going to be over-represented in the client base, and being poor correlates negatively with health status generally.

So we don’t have many good reliable data on the relationship between what we put into our bodies and our healthiness. Yet at the same time, most people have strongly held intuitive views about what is a healthy diet and what is not. You can tell how strongly held these views are when you try to challenge them.

Let’s take an easy target. Fast food. We all know that eating fast food is unhealthy. A diet of Pizza Hut, MacDonalds, Burger King and KFC is bad for you. But let me be provocative here. I’ve got a crazy theory. I reckon you could do a Morgan Spurlock and just eat fast food for a month, and be perfectly healthy at the end of it. The fact is, most people who eat fast food all the time get fat and genuinely are unhealthy. But I reckon this is largely because of their net consumption—they eat too much—allied with their lifestyles. In truth, it’s probably very difficult to be healthy on a diet of just fast food, but this is not because there’s anything intrinsically toxic about it, but because of the extremely high energy content of most of the dishes on offer. If Morgan Spurlock hadn’t supersized his meals, and had excercised more during his thirty days, I doubt there’d have been much of a documentary.

Our bodies are pretty good at regulating their weight, but the ‘calculations’ they make are thrown out of step by the unusually high energy content of Western diets. Thus we pack on the pounds when we eat what our body tells us is a normal quantity of fast food. If you had really good self control and under-ate, and you instituted a program of regular exercise, you could live perfectly healthily on fast food alone, although I don’t think this a prospect that appeals to me. But that’s aesthetics. We choose to eat what we do for perfectly valid reasons other than healthiness.

What do you need from your diet? Some protein, some carbohydrate, some fat, plus vitamins and trace elements. Perhaps some fibre, too. The body is pretty versatile, and an otherwise healthy adult would have to work quite hard in western societies to end up with a vitamin deficiency, or suffer some other form of malnutrition. And while enough of these vitamins and trace elements are needed for health, an excess doesn’t do any good at all.

Why is it that foods such as salad are good for you? It may well not just be because of anything intrinsically good about them—yes, they do contain some vitamins and trace elements, but an excess of these isn’t positive—but rather because of their displacement effect. If you eat five portions of fruit or vegetables each day, you are going to be eating less of other higher-calorie stuff.

A thorough analysis of the science of diet is beyond the scope of this piece, but let me illustrate the complexity of the relationship between diet and health with a couple of examples, beginning with the antioxidant story. Antioxidants such as vitamins C and E are present in many foods, and in theory should counter damage to cells from oxidation. This is what they do in experimental ‘test-tube’ trials. The widespread belief was that taking these antioxidants as dietary supplements should be health-promoting, but in large and expensive trials they failed. Why? It’s likely to be a problem of getting the oxidants to the right place at the right time for them to have their protective effect, known as ‘tissue availability’.

Look at the wine and health story. Wine is believed to be good for you, in moderation—at least that’s what large trials have shown repeatedly. But scientists are still arguing about mechanisms (how exactly does wine have its protective effect and what components are involved?), and some are suggesting that the benefit seen in trials is an artefact of confounding. Then there’s the really interesting pro- and pre-biotic story. Taking doses of ‘good’ bacteria helps populate your gut with the right sorts of microbes and is of some health benefit. Perhaps even more exciting is the finding that certain foods act as pre-biotics, and help make ideal conditions for these ‘good’ bacteria to grow in.

I hope this short piece has highlighted the complexity of the relationship between diet and health, and the scientific uncertainties surrounding it. We tend to have the notion that what goes into our mouths enters our bodies, and this then leads us to have a strong intuition that we really are what we eat – that the exact details of our diet are perhaps more significant in shaping our health than they really are. This makes us easy to dupe by pseudoscientific charlatans, and renders us susceptible to the spurious claims of dietary supplement manufacturers. We also tend to fall for concepts such as detoxing and colonic irrigation, which have little basis in reality. Perhaps a more rational understanding of diet, allied with the notion that much of what we eat stays outside the body in the gut, might help keep our thinking here.

Back to top