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The brain's role in weight: Why weight loss & weight loss maintenance are so challenging - Pt I

According to data from the CDC, each year roughly half of U.S. adults attempt to lose weight (1). While losing weight is challenging, maintaining weight loss can be even more so.


The typical belief – both within society and some of the medical community - is that weight loss is purely a matter of willpower or discipline (2). Yet within the last few decades, a substantial body of evidence has identified the role of the brain, in conjunction with other organs and a complex hormonal system, in maintaining body weight (2,3,4,5).


So what role does the brain play in maintaining our weight? And what does that mean for our weight loss attempts?


Homeostatic Regulation


It’s clear that our weight is a result of a complex combination of genetics, environmental factors, psychological factors, lifestyle and biological regulation. It is this latter system of which we will predominantly be focusing today.


There are many systems in our body that work to maintain homeostasis, or balance. For example, the level of sodium in our blood is well-controlled by a complex process ultimately involving our lungs, kidneys, liver, pituitary gland, and adrenal gland. If you consume too much fluid running the risk of diluting your sodium, your system kicks in to excrete more fluid and retain more sodium – and vice versa if you don’t consume enough fluid. This is a survival mechanism.


Our weight is actually quite similar. There are some who argue our weight has a set point, or a fairly tight range in which it likes to hang out. Several theories to explain this have been suggested over the years – the Set Point Theory, the Settling Point Theory, the General Model of Intake Regulation, and the Dual Intervention Point Model (6,7). We won’t go into all the detail of each theory here, but it does seem there are biological factors driving us to maintain our weight status, combined with psychological, lifestyle and environmental factors that exacerbate or support our underlying biology (7). So, what the heck does that mean for our health and weight?


It means that when you lose weight, your body is designed to promote you regaining the weight. Sometimes right back to where you started, sometimes a little less, sometimes even more.


Often people believe this is because their metabolism has reduced or been damaged by “dieting”. Or because they have no willpower, or they failed. Here is where the discussion of biology can be helpful, and what I mean by biology is how your body is physiologically working to manage its weight.


Your brain takes center stage in this production, primarily the hypothalamus. Your adipose tissue (fat tissue), gastrointestinal tract (and accessory organs, like the liver and pancreas), and muscle are all supporting actors. These actors are constantly sending messages (via hundreds of hormones such as GLP-1, leptin, and amylin) to your brain about your energy status or balance – are you losing weight, gaining weight, or maintaining weight? For example, if your adipose tissue balance is starting to reduce because you are losing weight, eventually your adipose tissue (and gastrointestinal tract) will start to send a message to your brain indicating as such, and your brain will work its magic to help you eat a bit more and move a bit less. Please keep in mind here that balance does not refer to health. Unfortunately, this system does not appear designed to keep us at a weight where we are healthy. It is truly designed for survival.


How these messages convert into action isn’t always straight forward. In my experience, some people do feel physically hungrier. Others just report having more cravings, thinking more about food, planning the next meal when they just finished the last one, having less “resistance” to foods when they are around. And interestingly, we also have data in animals suggesting your brain will start to convince you to move a little bit less to conserve energy. In other words, the brain is very tricky and subtle.


Just how strong is this system? Strong. In fact, the majority of current FDA medications approved for weight loss are functioning on this system in some capacity.


So, let’s say you’ve been a weight most of your adult life and start to gain weight. Why doesn’t the body fight this? Technically, it does try. There is an increase in hormones designed to curb hunger and a decrease in hormones that trigger hunger. Unfortunately (or really fortunately), this system appears much less strong than the other. Again, this harkens back to the ultimate goal of survival. Yes, our body wants to prevent too much drift above our “normal”, but it’s way more concerned with going too far below.


Of course, as alluded to above, this is not the only factor in our weight status. Lifestyle, environmental factors, psychological factors, other medical conditions – these may all contribute to what, when, and how much we choose to eat, how we metabolize nutrients, and whether or not we do any movement. There is also the pleasure center of the brain which drives eating habits, also known as the hedonic system. Once thought separate from homeostasis, it’s now believed these two systems overlap – which means hormones that impact physiological drive to regain weight may also be driving more pleasure in eating (8). I’ll talk more about the hedonic system in Part II.


If my brain is running the show, does that mean my weight loss attempts are all for naught?


Yes, this system is strong. But losing and maintaining weight loss, if appropriate for health and wellness, is not impossible. We have plenty of data noting that weight loss is not about one specific diet or one particular exercise (9,10). What seems more important is finding an individualized approach that not only creates the necessary dietary and activity change, but also helps you develop behavioral tools and a supportive lifestyle. At the end of the day, if losing weight is beneficial for health and wellness, and someone feels ready and wants to lose weight, it definitely requires seeing it as more of a marathon than a sprint.


Making and sticking with change takes mental energy, in particular due to this system. It’s hard work, and while everyone’s experience is individual, there are commonalities among those that maintain weight loss long-term. In part III, I’ll talk more about the common habits of characteristics of those maintaining weight loss.

1) The Centers for Disease Control and Prevention (2018) Attempts to Lose Weight Among Adults in the United States, 2013-2016. Available at: https://www.cdc.gov/nchs/products/databriefs/db313.htm.

2) Timper, K. and Bruning, J.C. (2017) ‘Hypothalamic circuits regulating appetite and energy homeostasis: Pathways to obesity’. The Company of Biologists, 10, pp. 679-689.

3) Roh, E., Song, D.K., and Kim, M.S. (2016) ‘Emerging role of the brain in the homeostatic regulation of energy and glucose metabolism’. Experimental and Molecular Medicine, 48, pp. 1-12.

4) MacLean, P.S., Bergouignan, A., Cornier, M.A., and Jackman, M.R. (2011) ‘Biology’s response to dieting: the impetus for weight regain’. American Journal of Physiology, 301(3), pp. R581-R600.

5) Casanova, N., Finlayson, G., Blundell, J.E., and Hopkins, M. (2019) ‘Biopsychology of human appetite: Understanding the excitatory and inhibitory mechanisms of homeostatic control’. Current Opinion in Physiology, 12, pp. 33-38.

6) Muller, M.J., Bosy-Westphal, A., and Heymsfield, S.B. (2010) ‘Is there evidence for a set point that regulates human body weight?’ F1000 Reports: Medicine, 2, pp. 59-66.

7) Speakman, J.R. Levitsky, D.A., Allison, D.B., Bray, M.S., de Castro, J.M., Clegg, D.J., Clapham, J.C., Dulloo, A.G., Gruer, L., Haw, S., Hebebrand, J., Hetherington, M.M., Higgs, S., Jebb, S.A., Loos, R.J., Luckman, S., Luke, A., Mohammed-Ali, V., O’Rahilly, S., Pereira, M., Perusse, L., Robinson, T.N., Rolls, B., Symonds, M.E., and Westerterp-Plantenga, M.S. (2011) ‘Set points, settling points and some alternative models: theoretical options to understand how genes and environments combine to regulate body adiposity’. Disease Models and Mechanisms, 4, pp. 733-745.

8) Berthoud, H.R., Munzberg, H., and Morrison, C.D. (2017) ‘Blaming the brain for obesity: Integration of hedonic and homoeostatic mechanisms’. Gastroenterology, 152, pp. 1728-1738.

9) Garvey, W., Mechanick, J., Brett, E., Garber, A., Hurley, D., Jastreboff, A., Nadolsky, K., Pessah-Pollack, R., and Plodkowski, R. (2016) ‘AACE/ACE Comprehensive Clinical Practice Guidelines for Medical Care of Patients with Obesity’. Endocrine Practice, 22(3), pp. 1-203.

10) Raynor, H. and Champange, C. (2016) ‘Position of the Academy of Nutrition and Dietetics: Interventions for the treatment of overweight obesity in adults’. Journal of the Academy of Nutrition and Dietetics, 116(1), pp. 129-147.

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