I did not expect that my previous post would prove so contentious and would lead to such a wide range of comments. Thank you for those, and for the detailed points made, and the references to published work. I must admit that I sometimes experienced an Alice in Wonderland effect: the discussion has veered away from what I had expected and involves many assumptions which I am trying to understand.
I did not expect that anyone would question the general principle of “calories in/calories out”. I am surprised, and have read the supportive arguments, but do not find them convincing, as I will explain later. I have also been presented with notions about the effects of different types of food, and the balance between protein, fats and carbohydrates. All these are digested down into the working fuel of the body. Eat too much of any or all of these, and your chance of getting fat increases.
Yes, of course these foods could have a different balance point between calories ingested and perceived satiation. If it is possible to choose foods which lead to quick satiation it might be possible to control weight, but only if there is strict control over how much is eaten. My argument, which some found difficult to follow, is that the main cause of obesity is eating too much, and the balance between food types is a secondary consideration to that.
As an obesity clinic at Addenbrook’s Hospital explains:
Obesity is the medical term for having too much fat stored in your body for good health. When people gain weight through a ‘positive energy balance’, that is more energy (food and drink) coming into the body than is being spent through activity and exercise, the surplus energy is stored mainly in fat cells that are present throughout the body. Nothing has to ‘go wrong’ for this process to happen.
I say that if you are over-weight and wish to lose weight, then you should eat less. You should keep eating less until you achieve your desired weight, and then stick to that level of calorific intake. What you eat is up to you, but a good rule of thumb is to reduce your intake of high calorie foods. If you need more guidance, avoid high density calorific foods and eat more low density low calorie foods. There are many published sources of calories for each food type, and some come with helpful pictures so that you can judge calorific intakes by sight.
Increasing your level of activity, by whatever means you choose, is unlikely to have much direct effect. This is because in current times there is so much good food available that you can replace half an hour’s calorie expenditure in about two minutes. A chocolate-coated nut-filled candy bar will do the trick. Short of the high levels of work of our Victorian ancestors, or of frequent treadmill exercise, this is not a viable strategy for losing weight in modern times. The only realistic strategy is to reduce calorie intake. Our metabolisms are very efficient, and food goes a long way. For example, couple a normal dietary intake with using a bicycle and you can achieve many miles per calorie ingested.
Do most over-weight people succeed in losing weight? Apparently not. This does not invalidate the advice that one should eat less. It reveals that people find it very difficult to follow that advice. The spirit is willing, the flesh is weak, all too much of it.
A few words on some familiar topics. You do not disprove a correlation by concentrating on residuals. A good correlation is not a perfect correlation: there will be discrepant instances. There will be individual variations caused by particular foods, digestive upsets, ill-health and other extraneous noise. Some people have a genetic leptin deficiency which denies them feedback about satiation. They eat too much because they still feel hungry. There will always be individual cases, even within the general observation that if you are too fat you should eat less. How much do these variations account for in the general population? Probably not much, in my estimation. However, let us imagine that they accounted for 10% of the variation in converting food calories into fat, such that some people get fat much faster than others on the same calorific intake. This would be a break-through in agriculture and stock rearing, and potentially commercially valuable. Thermodynamics is a general principle, and applies universally.
To attempt to disprove the “calories-in/calories-out” argument with some individual cases or short-term studies will not give you a true picture. Look at large samples over a longer time frame. If you are really in a hurry, look at the results of spending a night in the controlled circumstances of a calorific chamber.
The anorexia clinic at the York Clinic, Guy’s Hospital was not a calorific chamber, but it was a reasonably controlled environment. Some parents helped their children cheat the system, by taking out Complan in flannels in their handbags, fooling us into thinking that the emaciated adolescent was eating as required. However, we could detect the deception at the weekly weigh-ins, and could be sure that something was wrong by the second weigh-in, so close was the correlation between calories-in/calories-out in that controlled circumstance.
Here, as requested, are the summary data on the patients:
As you can see, these were patients who were about to die. They were emaciated, often very frightening to look at. It was painful to see them dying, yet still incapable of taking the steps to save themselves of their own volition. Happily, we never lost a patient in treatment.
Notice that although these patients gained weight, they did not do so at the same rate, an individual variation on a general effect. That said, they had a weekly weight gain which was similar, and predictable.
Another general note of guidance: people are not always reliable reporters about their food intake. Some of the discrepancies are caused by simple forgetting, but much is caused by wishful thinking and selective recall. Typically, people forget snacks between meals, and second helpings. They often ignore calorific drinks, mostly sugary ones.
Processed food is not bad in itself, but it is hard to monitor what is in it, and it is probably best avoided if you wish to lose weight, that is, it should not be a large part of your habitual intake.
In general, all foods are good for you, in moderation. There are circumstances when you may have to eat what is available, even if it is not the best basis for a permanent sustained diet.
Eating less is not a complicated strategy. Yes, at a very detailed level the way the digestive system works can always be investigated further, but enough is known to realise that eating less makes you less likely to get fat.
Specific diets are not really required. They are behavioural strategies to restrict food intake by disrupting over-eating habits. So long as the diet reduces calorie intake, it will work. Specific foods will not banish obesity unless they are low calorie foods. Diets work, but only if people diet. The difficulties they have in sticking to a diet whilst surrounded by large quantities of appetizing food are legion. We are easily distracted by immediate opportunities, and less concerned by postponable threats. Willpower exists, but it is a fragile disposition.
Although a genetic pre-disposition will make obesity more likely by reducing satiation feedback, that will only happen if you eat more than your body needs.
The body is a heat machine. Food is the fuel. Thermodynamics applies.