The below articles are not my own words but that of Zoë Harcombe. I have been discussing both of these issues with clients lately and felt I needed to get this message out. With this already being articulated so brilliantly I am sharing with you instead:
1) Energy in does not equal energy out
One of the favourite slogans of diet advisors is “energy in equals energy out”. They even add “you can’t change the laws of physics/the laws of the universe.” I don’t know if they know what the laws of the universe say.
The first law says: “In a closed system, in thermal equilibrium, energy can neither be created nor destroyed.” Energy can be changed from one form to another, but it shall be conserved. The human body, however, is not a closed system and it is not in thermal equilibrium (although it is continually trying to be there). So, we also need to consider the second law.
The second law (entropy) has been called the law of common sense – it says that energy will be lost and energy will be used up in making available energy and we need to take both of these into account. This is the law that proves that a calorie is not a calorie, as even Weight Watchers cottoned on to with their launch of ProPoints in November 2010. The energy used up in making carbohydrate, for example, available to the body as energy vs. the energy used up converting protein to usable energy is substantially different. 100 calories of carbohydrate eaten may make 93 available to the body; 100 calories of protein eaten may make only 70 available (Ref 1). That’s a significant advantage for dieters and helps to explain the effectiveness of low carbohydrate diets.
These ‘laws of the universe’ were developed during the industrial revolution to help understand if we could make a perfectly efficient steam engine. The laws were and are all about energy, not weight. The laws say nothing about weight being conserved – we humans flit between energy and weight interchangeably in the world of dieting and our conversions and assumptions are wrong.
The laws of the universe were never intended to become the fundamental principles of dieting. They do have some relevance to dieting, but only when they are correctly applied and when all the caveats are allowed for. There is simply no law that says energy in equal’s energy out. Even if there were, the corollary would surely be – less energy in equals less energy out, which brings us nicely to the second piece of knowledge…
Ref 1: Jequier, “Pathways to Obesity”, International Journal of Obesity, (2002). (See reference 29 on The Obesity Epidemic)
2) Eating less will NOT make us weigh less!
Similarly, doing more will not make us weight less.
It is an almost universally held belief that people who are overweight just need to eat less and/or do more. The idea that eating less will make you weigh less assumes that the body cannot and does not adjust. It can and it does. To think that if you eat 500 fewer calories the body will give up 500 calories of fat, to make up the difference, is the ultimate naivety in the world of dieting. The body is not a cash machine for fat.
Let us say that our average person has a basal metabolic rate (BMR) requirement for 1,500 calories a day (the number of calories the person would need if they were ill in bed all day – just to run all the activities done by the body). Let us then say that they have a requirement for 500 additional calories if they are up and about (this is a realistic estimate – the BMR is the main determinant of the calorie need for the day by a margin).
The idea that a reduction of 500 calories leads to the body giving up 500 calories of fat assumes that neither the BMR requirement (1,500 calories) nor the additional requirement (500 calories) change. In reality both change. The person who eats less has less energy and they will likely do less additional activity that day – they won’t go to the gym or walk to the post box – they will be too tired. The body will also cut back on its maintenance for the day – it can save cell repair, fighting infection and building bone density for another day – you haven’t eaten enough, so it can cut back.
Think about it – you lose your job – you don’t automatically dip into savings – you cut back on expenditure and the body does exactly the same.
The exact same applies for doing more. If you think that you can eat the 2,000 calories needed for the day and then try to do 500 more calories worth of exercise, with the body making no adjustment elsewhere, you are wrong. The body is highly likely to cut back on the additional calorie expenditure above the BMR. If you go to the gym, you may then sit on the sofa all evening – too tired to do the housework. The body can also reduce the maintenance it had planned to do for that day.
Furthermore, exercise and BMR require quite different calories. Exercise is arguably best fuelled by carbohydrate (it provides glucose quickly for the body to use). BMR activities need fat, protein, vitamins and minerals. Carbohydrates can be useful for the vitamins and minerals they provide, but the macro nutrient, the carbohydrate itself, can only be used for energy – not cell repair and fighting infection. Hence – if you eat 1,500 calories of carbohydrate (as the average citizen of the developed world currently does) – it can’t be used for body maintenance – you need to burn if off down the gym or you will gain weight.
Both the eating less and doing more beliefs also make the massive and wrong assumption that the body is able to burn fat. The body will always use carbohydrate for fuel first. Hence, if our average person has any glucose in the blood stream or any glycogen (stored glucose) in the body – this will be used to cover any gap in food eaten or activity done. The body can only burn fat when there is no glucose/glycogen available. Modern man rarely, if ever, allows his body to get to the state where it can burn its own fat – let alone will.
Eating less makes us want to eat more and/or do less. Doing more makes us want to eat more and/or do less. Neither eat less nor do more have worked, can work, or ever will work as a solution for the obesity epidemic.