In a recent BMJ editorial, an appeal was made to label foods with ‘the exercise needed to expend its calories.’1
At face value, this seems reasonable: ‘Eat that donut and you have to walk a km to make up for it!’ But an understanding of the complexities of bio-energetics shows how far it is off the mark. Couple this with the requirements for successful health promotion and you can see the trouble we have with prescription compliance in lifestyle-associated activities.
At the outset, we need to acknowledge that, despite ~100 years of blind acceptance of the opposite, a calorie is no longer a calorie! And yes, before you stop reading in disbelief, this statement refers specifically to the difference between a literal (physical) calorie and a practical (biological calorie). Absolute science shows that a physical calorie (the energy required to raise the temperature of 1g of water by 10 C) is as fixed as anything in science. Also, the 1st law of thermodynamics (energy is neither created nor destroyed, it just changes form) is immutable.
But this is the problem when confusing physics with biology: Biology is the living world, which is not inert but, most importantly, involves feedback! Only relatively recently have we begun to understand that linear (physics) models don’t work (or at least work only partially), when applied to live organisms. This has become even more obvious by the intervention of the newly highlighted gut microbiome in bio-energetics.
Put simply, 100 Calories in food or drink (note the large ‘C’ in calories as even this is confusing, with a small ‘c’ actually representing 1/1000th of a Calorie as defined above) can wind up being the equivalent of 50, or even 150 or 200 Calories depending on a range of feedback mechanisms within the individual consuming that energy. This will be determined by body size, metabolic rate, muscle-to-fat ratio, gender, the microbiome, and a range of other factors – some of which may not yet be known.
Labelling a food therefore as constituting 100 Calories and therefore requiring 1km of walking to expunge this from the body’s energy storage system is therefore misleading, as energy stores are also determined by metabolism and habitual activity levels. A 100 Calorie piece of carrot cake for example may require no extra exercise expenditure for an habitually active person (or, indeed, an obese individual), but a lot more for someone with a low resting metabolism.
The general presumption of energy intake balanced with energy expenditure, leading to weight maintenance, may not be a problem in itself, but can create an excess of guilt in some people unable to achieve this and for whom the guilt can be counter-productive for a healthy body weight.
And this brings us to the second point: Public health initiatives aimed at encouraging those at most risk of obesity, need to be accurate and finely target. Norwegian researchers have shown that a concentration of fruits and vegetable intake amongst younger age groups is likely to be more effective than a focus on calories. Similarly, the elderly are more likely to respond to a positive approach (eat more fibre) than a negative calorie counting (eat less fat/sugar) approach.
We know that calorie counting doesn’t work. It has failed us in the current obesity epidemic. We also know it creates more problems than it solves. So why even consider labelling foods with the ‘exercise needed to expend its calories’?
The body weight situation is complex; much more complex than a basic calorie trade off on food labels can illustrate. Its roots lie, not just in Mr and Mrs Everybody’s lack of understanding of personal responsibility in watching everything that goes into their respective mouths, but in food companies’ marketing of high energy-dense foods and drinks, governments bowing to industry lobbying and party funding, and even the system requiring exponential consumption for healthy economic growth.
So let’s get the discussion back on track: Labelling food with the exercise necessary to expend its calories is not only wrong, it’s a cop-out. The last people who should accept this are the medical profession and those involved in nutrition education.
- Cramer S. Food should be labelled with the exercise needed to expend its calories. BMJ 2016;353.