An extract from some info from Zoe Harcombe, reporting on some recent research, which explains why 'eat less/move more' doesn't work - I've bolded the key explanatioin:
Energy compensation & adiposity
Executive summary
A paper was published in August 2021, which generated the headline "Exercise reduces the number of calories burned at rest in obese people, study finds."
The researchers used the world's largest database on human energy expenditure. Data for 1,754 adults were used in this study
- Total energy expenditure comprises two main elements: basal energy expenditure and activity energy expenditure and two smaller elements: the thermic effect of feeding and non-exercise activity thermogenesis.
- Three energy expenditure models were hypothesised and then tested for validity. The researchers found that the energy compensation model was the valid one. Energy compensation was defined as “the concept that not all the energy spent when activity levels increase translates to additional energy spent that day.”
- The two key findings were that 1) approximately 72% of the extra calories spent on additional activity translated into extra calories burned that day and 2) energy compensation is particularly high in people with higher BMIs.
- The EarlyBird study (which dates back to the mid-1990s) also found that extra activity is compensated for by reduced activity elsewhere during the day.
- There are thus a number of ways in which do more (and also eat less) conspire against us so that the body does less rather than giving up body fat. The additional (cruel) finding of this study is that the compensation is larger in those with higher BMIs.
Introduction
The paper, which is the subject of this week’s note, was published at the end of August 2021 (Ref 1). It complements last week’s note nicely, as it’s the flip side of the energy balance coin. It received good media coverage with the headline “Exercise reduces the amount (sic) of calories burned at rest in obese people, study finds” (Ref 2)
Before we get into the study, we need to revisit the calorie theory and the current belief that holds for weight loss. It is believed that the creation of a deficit of 3,500 calories will result in the loss of one pound of body fat. In all my years of research, this is probably the most absurd thing that I have ever come across. As Blackadder would say “it is wronger than a very wrong thing!” The theory says that it doesn’t matter who you are (age, sex, BMI, body fat, previous dieting history, other conditions etc.), create a 3,500-calorie deficit and you will be rewarded with a loss of one pound of body fat. The fact that the body needs to be in a physiological state to be able to burn body fat (no insulin present, no glucose/glycogen available, a requirement for fuel and glucagon able to be called upon) is completely ignored, as are so many other factors
The 3,500-calorie theory assumes that the body is a cash machine for fat. For every 3,500-calorie deficit, one pound will be released. One of the many assumptions upon which the calorie theory relies, is the notion that the body cannot and does not adjust in any way. The body can and does adjust. The body has a number of systems (nervous, skeletal, endocrine, reproductive, digestive, circulatory, lymphatic, urinary, respiratory), which can and do adjust. The condition of anorexia illustrates what can happen at extreme calorie deficits. The reproductive system shuts down within weeks of significant calorie deprivation. The person becomes cold, the brain functions less well, the skeletal system is impaired and long-term damage can start, the digestive system becomes sluggish – everything can and is put into survival mode
If we take the typical female as is our usual example – she needs approximately 2,000 calories daily. For simplicity we will view those calories as needed for basal metabolic purposes (approximately 75% i.e., 1,500 calories) and for energy (approximately 25% i.e., 500). The calorie theory assumes that, if she cuts back by 500 calories daily, she will have lost one pound of body fat by the end of the week. This assumes no adjustment whatsoever. Evidence shows that the body can be ‘tricked’ in the very short term and weight loss does occur with a calorie deficit diet initially. (It does not adhere to any formula, however, and it occurs less well for each and every subsequent calorie deficit diet). It doesn’t take long for systems to adjust to the reduced energy intake. The body then responds to ‘eat less’ with ‘do less.’ If we don’t provide the fuel (the right amount and the right kind) for the body systems, the body will turn them off (reproduction) or turn them down (building bone density). Eating 500 fewer calories can lead to 500 fewer calories worth of repair and maintenance being done
This week’s paper has shown that, just as eating less can lead to the body doing less, so doing more can lead to the body doing less. If calories are expended in deliberate activity (exercise), the body doesn’t just give up body fat – it can do less of what it planned to do that day (fighting infection, cell repair and so on). This makes complete sense, but it still needed to be shown and this paper has done so