By Julia Katcher, Registered Dietitian and PhD Nutrition Science Student
CONTENT WARNING: For researchers to obtain funding to carry out studies, most investors and grants require biological measurements such as height and weight instead of self-reported data alone. Because of the simplicity behind Body Mass Index (BMI), many of these papers mention BMI classes. This does not mean we support BMI, as we believe BMI is not a good indicator of health. If BMI references are triggering for you, please do not click on the links to the research and just read this blog post.
Have you tried to lose weight by adjusting the energy balance equation (by moving your body more or consuming fewer calories) and experienced your body making its own adjustments, no matter what you do? There is scientific data that provides evidence that weight re-gain is a by-product of dieting; people typically end up back at their starting weight or heavier following weight loss. So why does this happen?
BODY WEIGHT HOMEOSTASIS
Our bodies can overrule our attempts to manipulate our weight! The way that our bodies "overrule" our attempts to lose weight is through homeostasis - which is our body’s ability to maintain internal conditions despite external changes. A great example of homeostasis is body temperature; our bodies need to stay within a certain temperature range to survive, otherwise our bodily functions begin to malfunction. For example:
- • When we exercise hard, we start sweating to cool our bodies down.
- • When we’re exposed to cool air, our bodies will start shivering or our tiny hairs will become raised to trap heat in.
The same concept applies to weight regulation - our bodies are hugely successful at deploying mechanisms to regulate our weight (i.e. maintain internal conditions), despite how we manipulate our eating and activity (i.e. external changes) - this is called Body Weight Homeostasis.
From an evolutionary standpoint, our bodies were designed to fight off starvation and conserve enough energy until we could find our next meal. Because of this, our biological mechanisms are designed to favour weight gain over weight loss; this shouldn’t be too surprising since this is how we’ve survived as a species!
There are a few theories that explain why our bodies defend a certain weight range and each theory is supported by certain mechanisms and conditions our bodies undergo. We’re going to discuss the two theories that are the most supported in research - set point theory and settling point theory.
Set point Theory
Set point is the weight range in which your body is programmed to function optimally. Set point theory holds that one's body will fight to maintain that weight range.
The hormone leptin is produced by the fat cells in our body and helps to control our appetite and energy expenditure. When hormone signalling is functioning the way it should, this feedback control system works to put one back into the set point weight range: when leptin levels are low, our hunger increases and energy expenditure decreases and when leptin levels are high, our hunger decreases and energy expenditure increases.
Note that these hormone signalling mechanisms can be disturbed when body fat increases and leptin increases to the point where the individual becomes leptin resistant.
Our genes also play a role in determining our set point weight range. Gene mutations that affect weight are rare (e.g. Prader Willi Syndrome, which is a genetic disease that leads to weight gain as the disease progresses). However, in terms of our genes' role in weight regulation, studies are showing that it’s more important how our genes react with our environment, which can play a role in how our weight is regulated.
So set point theory surmises that ones weight can drop below the set point range if we're eating less and moving more, but any weight loss is short-term and unsustainable due our body weight being regulated by our hormones and genes.
Settling Point Theory
Settling point theory is a model of body weight regulation that takes into account factors that are not covered by set point theory: predominately, how environmental factors can play a role in body weight regulation.
In the settling point model, it is assumed that there is little active predefined regulation of body weight, but that this settles determined by environmental and socioeconomic factors, such as diet and lifestyle, in interaction with genetic pre-disposition. Precise regulation takes place without a fixed set point, rather body weight settles based on that resultant of a number of contributors.
Weight regulation isn’t 100% understood and it’s difficult to do studies on weight regulation in humans as each person’s body weight is influenced by their individualised factors, and not each factor can be accounted for on an individual basis. Not one theory alone perfectly explains our body weight regulation. We hope this you can make peace with your body and the genetic blueprint it comes with.
DISCLAIMER: This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding your medical condition.
- Herman, C.P., & Polivy, J. (1980). Restrained eating. In A.J. Stunkard (Ed.), Obesity (pp. 208–225), Philadelphia: Saunders.