The Role of Adaptive Thermogenesis in Resistance to Weight LossWednesday, August 8, 2012
Sooner or later every diet, every medication, or every type of bariatric surgery will result in a weight loss ‘plateau’ (better referred to as a ‘floor’) – a weight, beyond which losing even more weight (and keeping it off) becomes an almost ‘super-human’ feat.
However, there is considerable variation in how much weight people can lose and keep off. Although the average sustainable weight loss with ‘eat-less-move-more’ (ELMM) approaches is about 3-5% of initial weight, some folks manage to lose considerably more, while others struggle to even simply stop gaining weight.
This has less to do with motivation or will-power than most people think.
In fact, it has far more to do with how your body adjusts to and is capable of resisting a calorie deficit.
While putting less fuel in the tank of your car will consistently decrease the distance that you can drive, our bodies adapt to less fuel (i.e. eating fewer calories) by becoming more ‘efficient’ and running the same distance on less fuel than before. That is the big difference between simple physics and biology.
Biological systems adapt – physical systems (like your car) stay the same.
In the case of humans (and animals) we call the adaptation of energy needs and expenditure ‘adaptive thermogenesis’.
Exactly how adaptive thermogenesis is regulated and how differences therein can largely determine both weight loss and weight regain, is the topic of a paper by Angelo Tremblay and colleagues from the Universities of Laval and Ottawa, published in the International Journal of Obesity.
As the authors point out,
“The decrease in energy expenditure that occurs during weight loss is a process that attenuates over time the impact of a restrictive diet on energy balance up to a point beyond which no further weight loss seems to be possible. For some health professionals, such a diminished energy expenditure is the normal consequence of a progressive decrease in the motivation to exercise over the course of a weight-reducing program.”
Many studies have now documented the process of ‘adaptive thermogenesis’, whereby weight loss is associated with a ‘greater-than-predicted’ decrease in energy expenditure. This occurs both through a reduction in metabolic rate as well as through an often remarkable increase in ‘fuel efficiency’ related to physical activity, whereby individuals, who have lost weight burn far fewer calories for the same amount of physical activity than before losing their weight (far more than can be explained simply by considering that they are also moving less weight around).
As the authors discuss, not only do people, who demonstrate the greatest decrease in adaptive thermogenesis in response to weight loss tend to lose less weight (for the same level of caloric restriction) but they also tend to have a greater increase in hunger and appetite.
Also, it does not appear that these ‘adaptive’ responses to weight loss diminish over time, which means that the resistance to further weight loss and the propensity to weight regain persist till the weight is eventually regained (i.e. they once again ‘fail’).
Together, these factors can easily explain why losing weight and keeping it off is far more difficult for some folks than for others – irrespective of motivation or will power.
This basic biological fact is not only important to ‘dieters’ (even if it seems demotivating) – but perhaps even more important for all health professionals to be aware of.
Simply ‘blaming’ people who find it harder to lose weight or keep it off for their lack of will power or motivation, is neither fair nor helpful.
You can only fight your biology so far before life is no longer fun – this is when you need to realise that you are now living below your ‘Best Weight’.
Tremblay A, Royer MM, Chaput JP, & Doucet E (2012). Adaptive thermogenesis can make a difference in the ability of obese individuals to lose body weight. International journal of obesity (2005) PMID: 22846776