Healthy Eating: What is the truth about fat and nutrition?

| 13th November 2012
With the present state of research we will never find out what we should and should not eat – but, says Colin Tudge, it is hard to improve on ancient wisdom and common sense.
Nutrition in general is a much neglected subject

I have been following the unfolding theories of nutrition for the past 40 years and in that time the advice from on high – and indeed from all sides – has swung spectacularly: from protein is all to protein takes care of itself; from fat will kill us to fat doesn’t matter; from fibre is just for cranks to fibre is the elixir of life; and so on.

Who should we believe, and on what grounds?

In any one decade (whether it’s the 60s or the 80s or the present day) the people offering nutritional advice fall into one or other of four categories. Some (1) are excellent scientists who really are trying to find out what is true. Some (2) want to know what is true but are not such good scientists. Some (3) have axes to grind – either commercial (they work for Nestle or have a book or a clinic to sell); or are evangelical (vegan, macrobiotic, whatever). Finally, (4), some have great insights but are not part of the scientific mainstream so they cannot produce stats of the kind that are counted as evidence and are not taken seriously. Many of those in category (4) are truly wise but difficult to assess “objectively”. Only your own intuition can tell you whether somebody else’s intuition should be taken seriously.

The excellent scientists, (1), as excellent scientists always do, approach their work with humility. They know that in the end, life and the universe are beyond our ken. Only idiots and mountebanks talk of total understanding and of “controlling” or “conquering” Nature - for in living systems in particular, there are too many factors to be taken into account, many of which at any one time are unknown; and as Donald Rumsfeld said in a somewhat different context, there will always be an unknowable number of “unknown unknowns”. In recent decades too the general idea of non-linearity has taken root: that there is no simple relationship between (putative) causes and (apparent) effects.

Nutrition in general is a much neglected subject

In nutritional science the problems are particularly difficult. Nutrition in general is a much neglected subject. A great deal that is obviously of great significance – such as the absolute importance of what might be called “micro-micro nutrients”, or what the pharmaceutical industry now likes to call “nutraceuticals” (including plant sterols etc, is only just coming to light; and although the pharmaceutical industry is already cashing in, almost nothing is known of these micro-micronutrients, compared to the myriad complexities that are obviously out there. Even more strikingly, microbiologists are now only getting to grips with the gut microbiota which are clearly of huge importance, as discussed earlier this year in Nature magazine (September 13 2012 pp 220 – 241).

In addition, in matters of human nutrition, cause and effect can only be inferred. In particular, medics place great store by the double-blind controlled trial. But a controlled trial that would truly test the relationship between fat and heart disease (say) would need to explore the effects of totally controlled diets on matched groups of human beings over their entire lifetime - and preferably for several lifetimes to account for inherited epigenetic effects (the importance of which, again, is only now being realised).

At the best of times, controlled trials of this kind have various theoretical flaws, and in this case of course the desired trial cannot be done at all. So scientists who sincerely want to find out the truth must rely on laboratory studies on animals (the wrong species; and too short a time); or on epidemiology (broad brush studies of what people do when left alone – the right species and “realistic” but of course uncontrolled); or studies of people in special circumstances (e.g. vegetarians – but the groups are rarely big enough to give statistically valid results and the groups are self-selected and may not be representative of the population as a whole). As always, too, the study group is likely be doing a great many things that have nothing to do with food but which may affect the results anyway (e.g. vegetarians possibly smoke less than non-vegetarians, or have better or worse social lives, or whatever).

In practice, the best overall study of the fat-heart disease problem that I know about was by the UK’s Royal College of Physicians (RCP) in 1976. It had loads of data - animal experiments, epidemiology, etc; but they made very clear the points that I am making here – that all of the data was flawed in different ways. In the end these scientists concluded from all kinds of clues that “the balance of probabilities” pointed to a positive correlation between high fat diets in general and heart disease, and in particular to diets high in saturated fats; and although correlation is not cause, they felt there was good reason to suppose that at least to some extent, the high fat diet was indeed causing the disease.

So they recommended reducing overall fat intake from the 40% of total calories which was normal in the West, to below 30%; and a general shift from saturated to unsaturated. (Mediterranean peoples in those days typically had a 20% fat diet, rich in mono-unsaturated olive oil – and very little heart disease). But in the spirit both of good science and of good medicine, the physicians stressed that no-one could be certain about any of this, and that the conclusions were purely statistical (i.e. you could reduce your chances of avoiding heart disease but could not guarantee a coronary-free life and if you did live long and health-trouble-free you would never know whether it was the diet that had rescued you); and so on. But then, physicians always have to make recommendations (because their patients ask them to) on the basis of imperfect evidence (because evidence can never be “perfect”).

Many people since this study have seized upon those cautious science-based recommendations and turned them into edicts and dogmas. This happens.

Also since the 1970s – and of crucial importance – nutritionists in general have begun to appreciate that there is far more to fats than meets the eye. In the 1970s and in general people said, “animal fat = saturated; plant fat (oils) = unsaturated”. Now it is clear that the chemistry of animal fats differs enormously from species to species, possibly from breed to breed – and certainly varies a great deal because of feeding. In particular it is now becoming clear that the fat of pasture-fed beef has far more unsaturated fat than that of grain-fed beef, and (in general) that animals that are fed on mixed, natural (or natural-ish) pastures have a fat profile that is more complex and generally more favourable to the consumer than that of animals fed on high-protein, high-sugar monocultural rye-grass. In other words, nutritionists are beginning at last to realise that nutrition isn’t just a simple exercise in simple organic chemistry.

In character (given the number of unknowns) nutritional science is far more like ecology. The RCP scientists in the 1970s were, perforce, studying the effects of diets that were not only high in meat and therefore in animal fat, but were high in grain-fed meat – because in the 1960s in particular when oil was cheap (and so too therefore were nitrogen fertilisers) there was a lot of grain-fed beef about. Now it seems very likely that a diet rich in pasture-fed beef would give a different impression. But the physicians in the 1970s did not have the opportunity to make the comparison (even if they had realised its importance).

Now we have another serious complication. Governments like that of Britain no longer support the kind of dispassionate research that the RCP carried out in the 1970s. In agriculture at least, big studies are left to big commercial companies. Big commercial agro-companies favour grain-fed beef which is cheaper to produce so long as the oil continues to flow to provide the fertilisers, and so long as the collateral damage remains un-costed.

If big companies promote grass at all, they want it to be heavily fertilised monocultural rye-grass. So they will not undertake trials to tell us if there really is a serious difference between the fat produced by beeves fed on concentrate, and that of truly pasture-fed animals – and neither will anyone else. So we have a double whammy. We now know that the problem is far more complex than was ever conceived in the past. But our elected government and the previous four governments have abandoned responsibility for the truly objective science that could help us to uncover the truth. In effect, intellectually, and morally, successive governments have abdicated. They merely occupy the various offices and build up their pensions. In short, the relationship between fat and disease will always be less than certain; but at present the relationship is far less certain than it need be, and there is no satisfactory resolution on the horizon.

Investigators and advocates in categories (2) and (3) muddy the waters still further. Some scientists frankly are not great thinkers but they go through the motions and if they produce results that please their commercial/government sponsors then their work gets published and written into the lore. Many others (3) may or may not be scientists but if they say things that hit the right buttons – which you can do up to a point simply by being iconoclastic – then they too tend to be believed.

The category (4) people just fall into the general category of “wise”: including a lot of local farmers and cooks who in a general way say that if you just eat what grows naturally and is raised kindly then you probably won’t come to much harm (which, given present knowledge of micro-micro nutrients, seems eminently sensible).

I like simply to observe that all the nutritional advice of the past 40 years – all the kind that feels most plausible – can be summarized in nine words: plenty of plants, not much meat, and maximum variety.

The farms should as far as possible be organic – in line with Nature itself – and the animals should be fed on diets that conform as closely as possible to what they are evolved to eat: cattle and sheep on pasture and browse; poultry and pigs on swill and crop surpluses – with as much access as possible to natural pasture and browse.

“Plenty of plants, not much meat, and maximum variety” also summarises the structure of all the world’s greatest cuisines. So if we farm along traditional lines and re-learn how to cook we can’t go far wrong.

We can throw a lot of science at this (saturates v unsaturates, “nutraceuticals”, and so on) and philosophy of science as well (non-linearity, uncertainty, correlation and cause, and so on) but in the end it is hard to improve on tradition and common sense. But then, common sense takes high-fallutin’ principles of non-linearity and complexity in its stride. It comes for free. 

In some circles at least, nutritional science is undergoing a paradigm shift: from the age of organic chemistry, to a true age of biology, in which we begin to appreciate life’s true complexity and innate uncertainty and see that in the end life is beyond our ken.

But if you want to maximise wealth then it is better not to dwell on the complexities, but simply to promote - with all the wiles of modern PR - whatever can be sold most cheaply in the greatest quantities. The neoliberal market economy, good objective science, and common sense do not make comfortable bedfellows.

Colin Tudge is a biologist and author. This article was first written for The Campaign for Real Farming

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