If you ask the average person in the street about weight loss, you will likely be told that losing weight is simple: “calories in = calories out”, so just “eat less and do more exercise”. This “energy balance model” has been deeply ingrained in us all since childhood, and superficially it sounds obvious and inarguable. Yet, if we all know this to be true (and are constantly reminded of it, including by healthcare professionals) and it is so simple, then why do we continue to see obesity rates escalate so dramatically?
The answer is that the energy balance model is flawed, unscientific and deeply unhelpful. If I could give one piece of advice to anyone looking to lose weight or to be generally healthier it would be to forget all about calories and to never count, or even think about, them again.
The energy balance model (energy in must equal energy out, or the excess energy will be stored as fat) is a concept borrowed from physics. The problem is that we are not machines or coal burning furnaces, we are animals, and we need to be thinking about biology rather than physics.
Adherence to the unscientific dogma around calories has resulted in significant harm including contributing to the current epidemic of obesity and diabetes, by pushing us away from healthy natural fats (because they are high in energy/calories) towards unhealthy processed carbohydrates. In fact, the only thing that the energy balance model has achieved has been to drive us to stigmatise overweight people as either greedy (too many calories in) or lazy (not enough exercise/calories out), or more often both.
Energy expenditure
Let’s start with the “calories out” side first. The single most common mistake people make is to equate “calories out” with exercise e.g. going to the gym or jogging. In fact, the majority (60-70%) of the energy we consume in our food is used to keep our basic bodily processes ticking over such as breathing and temperature control. This is known as our basal metabolic rate and will remain the same whether we are active or we just lie in bed all day. A further 10% is burnt up in digesting, absorbing and processing the food we eat. The remaining 20-30% is used up through physical activity. However, the majority of this energy is used up in lower intensity, daily, unplanned activity such as moving around the house, fidgeting, standing etc. This is known as “non-exercise activity thermogenesis” or NEAT) and it is often subconscious. Only a tiny percentage of the energy we expend is used for exercise such as running, estimated to be around 5% or lower in most people. So, simply changing the amount of exercise we perform is unlikely to have a meaningful impact on our energy balance and unlikely to impact our weight. We can see for ourselves that exercise has minimal impact on weight because people living in countries like the UK 60 or 70 years ago were far less likely to be overweight or obese yet very few people exercised back then, and literally no-one was going to the gym for a spinning class after work!
Energy in
Considering the “calories in” side of the equation also throws up some challenges. Firstly, calorie labelling on foods is notoriously unreliable. More importantly, even if you do know how much energy there is in a food it tells you nothing about how much energy our bodies will actually absorb from the food when we eat it. We might absorb most of the energy in the food, or much of it might pass through our gut without being digested and absorbed. The amount we absorb from food will vary between individuals, affected by our genetics and our gut microbiome. It will also vary depending on the composition and structure of the food, for example how much fibre there is in the food – this is why the calorie labelling on healthy foods such as nuts is misleadingly high.
“Energy out” will change depending on “energy in”
Finally, one of the most important principles to understand is that the amount of energy we take in and the amount of energy we expend are not independent of one another. Going back to biology, we are animals that are highly evolved to survive threats like prolonged periods of starvation. If we try to reduce our calorie intake to lose weight by creating a negative energy balance, we will see some initial weight loss. However, our bodies will perceive this as a period of starvation and what will inevitably happen is that our bodies will very cleverly (and entirely subconsciously) reduce the amount of energy we burn, in order to protect our energy reserves. So our basal metabolic rate will drop as will the amount of physical activity we do. Alongside this the body will pump up our hunger hormones driving us to find food to end the “starvation”. Overall, we will feel cold, sluggish and ravenously hungry. Sound familiar? The net result is that we will regain all the weight we lost and in fact our bodies will overshoot and our weight will rebound to an even higher level than when we started, yet another clever defence mechanism against starvation.
Time to think differently
Focusing on calories and the flawed energy balance model has caused a lot of harm. I would urge anyone who is considering a weight loss approach based simply on creating a negative calorie balance (eating less and/or exercising more) to stop and reconsider. We need to consign the calorie balance doctrine to the bin where it belongs and replace it with a new framework that is more scientific and ultimately more helpful to us. We are animals, and our bodies are under the control of hormones, not calories. We need to think about the impact of the food we eat and our physical activity on those hormones. Far better models for considering weight loss are based on these hormonal systems and include the Carbohydrate-Insulin Model and Weight Set Point Theory - I will address both of these models in future posts.
Dr Neel Gupta July 2023