It may be a hazard of working in a medical school, but from time to time I have felt the need, on the basis of some apparently valid research, to change my diet somewhat. At one stage that involved eating more fibre (unpleasant results and unnecessary investigations) eating much more fruit (same, plus higher bills) reducing the amount of red meat and bacon (increased gloom, slightly lower bills), taking and not taking vitamins, and other similar variations.
Come to think of it, I was probably responding to the media rather than any of my colleagues, since no-one in the staff dining room took any notice of such things. It was also there that I learned the basic metabolic formulas which revealed that humans are efficient and burn relatively few calories in normal daily activities, so if you want to keep slim you have to reduce your food intake. The key to avoiding being fat was: Eat less.
I have tried to cover these issues in a previous post “Fat is an intellectual issue”
If a good diet leads to good health, then any person of normal intellect should be able to work out what is required to maximise their chance of a healthy and long life. In modern life, working out what to eat is an IQ test.
Now we get two useful publications to assist us in making these decisions. The first is a paper in the New England Journal of Medicine by Casazza et al. (2013) entitled “Myths, Presumptions and Facts about Obesity” http://www.nejm.org/doi/full/10.1056/NEJMsa1208051#t=article
With a title like that, the paper is riding for a fall. I cast a belligerent eye on this 20 author publication, expecting the worst. They condemn, for lack of evidence, the following myths (beliefs held to be true despite substantial refuting evidence):
1) Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.
2) Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.
3) Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.
4) It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.
5) Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.
6) Breast-feeding is protective against obesity.
7) A bout of sexual activity burns 100 to 300 kcal for each participant.
In deference to those of my readers who cannot read the whole paper because they are about to have sexual intercourse: in reality it burns only about 14 calories more than watching television, apparently.
Anyway, all 7 of these claims have been refuted by reasonable studies. Having got rid of 7 myths, they then tackle 6 presumptions (widely accepted beliefs that have neither been proved nor disproved):
1) Regularly eating (versus skipping) breakfast is protective against obesity.
2: Early childhood is the period in which we learn exercise and eating habits that influence our weight throughout life.
3: Eating more fruits and vegetables will result in weight loss or less weight gain, regardless of whether any other changes to one's behavior or environment are made.
4: Weight cycling (i.e., yo-yo dieting) is associated with increased mortality.
5: Snacking contributes to weight gain and obesity.
6: The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity.
In pure Scottish: these are not proven. Probably best forgotten, in my view, but new evidence may yet emerge in their favour.
What do they list as proven facts? Moderate environmental changes can promote as much weight loss as medical drugs; reduced energy intake reduces weight, but dieting is difficult; exercise increases health regardless of weight; sufficient exercise improves weight maintenance; parents need to be involved in helping overweight children; regular meals promote weight loss; weight loss can be achieved by sustained taking of medical drugs; in appropriate patients bariatric surgery results in long-term weight loss.
So, eat less, though eating less is difficult, and in the US both drug companies and surgeons are after your money, some of which you can save by eating less in the first place.
They reflect: “When media coverage about obesity is extensive, many people appear to believe some myths simply because of repeated exposure to the claims. Fortunately, the scientific method and logical thinking offer ways to detect erroneous statements, acknowledge our uncertainty, and increase our knowledge.  Moreover, we often settle for data generated with the use of inadequate methods in situations in which inferentially stronger study designs, including quasi-experiments and true randomized experiments are possible. In addition, eliminating the distortions of scientific information that sometimes occur with public health advocacy would reduce the propagation of misinformation.”
My preliminary impression is that I warm to these authors, all 20 of them, when they are knocking down the myths and presumptions, but I think they pull their punches on the facts section. They stress that wanting to go on a diet and being told to go on a diet doesn’t usually result in the sustained maintenance of the diet. Fine, but we are talking about obesity. They note that “energy reduction is the ultimate dietary intervention” and that nothing else works unless “accompanied by an overall reduction in energy intake”. The English for that is: “Eat less”. Pity they put it as Fact 2, and buried it somewhat as an implication. Get that fact in your mind and you will have no need for surgeons. The way the authors handle it, that crucial fact has little impact. I cooled to them at the end. They started well, and then petered out.
Next up is Prof David Colquhoun, who focuses his sceptical eye on the broad range of diet claims and briskly asserts: We know little about the effect of diet on health. That’s why so much is written about it.
First off, Colquhoun draws attention to the long list of conflict of interests listed by the Casazza paper authors above, including many food manufacturers, which he says complicates an already messy field. He goes on to quote with great approval a paper BMJ 2013;347:f6698 doi: 10.1136/bmj.f6698 (Published 14 November 2013) by John Ioannidis. I will summarise the main points of the suggested references, with additional comments.
Most nutritional studies are observational, not experimental, and depend on questionnaires. There is always a nagging doubt as to whether every bacon sandwich and slice of chocolate cake will be faithfully reported, under the strain of recalling in vivid detail every lightly boiled cabbage and spoonful of cottage cheese.
Epidemiologists sometimes forget that people differ. Some are compliant boy scouts, some irresponsible spirits who don’t return questionnaires or follow instructions. Humans differ in intelligence and personality, but these considerations do not normally darken the door of diet epidemiologists. As far as they are concerned, people are what they eat, or become so after a decade of imprudent gluttony. Indeed, the meme “you are what you eat” seems to have had a great impact, despite being demonstrably false. Curious, the power of ideas, even stupid ones.
Even when semi-controlled trials are carried out, there is no way to ensure compliance, fall out from trials is rife, and sometimes the comparison conditions have to be made palatable by being only slightly different from the local cuisine (such that the low fat option is 37% fat, not the usually recommended 10%).
Then come all the odd and implausible results, such as that those that suggest we can halve the burden of cancer with just a couple of servings a day of a single nutrient (insert your favourite health food here). Miracle claims of this sort circulate widely in peer reviewed journals.
The other gripe among the cognoscenti? You read it here first. The sample sizes are too small, not followed long enough, and with high levels of sample attrition. Whoever you are, you cannot get round sampling theory. Samples of about 70,000 followed until death (with a proper link to death registers) will be required to identify even a few general patterns in diet which might account for a 5-10% increase in risk. If the studies are to mean anything, IQ, personality, sociological and occupational variables will have to enter the mix, and participants will probably have to be paid to stick to the course, and put up with random visits of inspectors looking in the fridge and the medicine cabinet. Count me out. So, although these correct and worthy researchers want controlled studies, they are not going to get them. Liberty will triumph over the food police.
After much thinking about how we can ever prove causality between diet and health, Colquhoun concludes that the only thing we can say at the moment with the remotest level of confidence about diet is:
Don’t each too much, and don’t eat all the same thing.
In shorter words, eat less.
That advice should be clear to all levels of intellect.
Disclaimer: Dinner was a microwaved Indian meal with curried chicken Madras 163, rice 269, potato cauliflower spinach 147, and nan bread 138, so a total of 717 calories, and then there was a large portion of home-made apple crumble and yoghurt. So, as the labels prove, a total of 717 calories.