Weight Loss Series

Biology’s a B*tch!

Why is it so hard to lose weight and keep it off?

Part 1 of a 6-part series on weight loss

Do you find it hard to stick to your weight loss plan?  Have you tried to lose weight and found the pounds won’t come off easily — or they come right back?! You are not alone.

The fact is, when we shed pounds mechanisms are triggered that make it hard to both lose weight and keep it off. Some factors are within our control, but many are not.  Understanding how the biology of weight loss works will allow you to be patient with the process and kinder to yourself.

Obesity is a real medical condition.  It’s inherited by our genes; it’s centered in our brain; it’s influenced by our environment; and weight loss efforts affect our metabolism.  This is why weight loss is not as simple as — eat less, move more.

Today I will be discussing two important aspects of weight loss — what is happening in our brain to cause weight loss difficulties (loss and regain) and what is happening to our metabolism.

70% of our ability to lose weight and keep it off is regulated by our genes…70%…thanks mom and dad!  We have inherited an appetite system that consists of 3 layers:  The homeostatic system, the motivation system and the executive system.

These appetite systems were

developed a long time ago, in a time when food was scarce and acquiring food took both hard work and motivation.

So how does this work?

The first layer is the homeostatic system, which defends against fat loss.  When this defense mechanism was developed, losing weight was not desired because weight loss meant famine and survival issues.  Weight loss triggers a hormone cascade and when the homeostatic system notices these hormone changes it sets off an alarm in our brain – it doesn’t matter if this weight loss is intentional.

This alarm sets off the 2nd layer – our motivational system.  When this system is activated, we are motivated to eat.  We might recognize this as a feeling of wanting or craving – these are unconscious feelings (or thoughts) beyond our control.  This system is also activated by learned activities, for example snacking at night – if you snack every time you sit on the couch and watch Netflix, then your motivational system will learn a snack is needed as soon as you sit on the couch.

The final layer is our executive system.  This is the only layer that is conscious, both the homeostatic and motivational systems are unconscious.   When the wave of wanting arrives at our executive system – we can choose to eat or not –but in most cases our executive system is sleepy.  A sleepy executive makes it difficult to evaluate the wave of wanting or craving.  To evaluate these feelings (thoughts) we need to determine if we want/crave food because we are actually hungry or is sitting on the couch triggering a thought.  A wanting thought may sound like: “it’s been a long day I deserve this” or “I am tired this will give me a boost of energy” or “I can have more because I exercised today”.  Is this starting to sound familiar?

If we can wake up the sleepy executive then these thoughts can be evaluated.  An alert executive takes the time to think slowly, deliberately, weighing consequences and will recognize unhelpful, inaccurate thoughts.  An alert executive can form his own thoughts that consider the future “I don’t really need this” or “I am not really hungry” or “I feel better if I don’t”.

Let’s overview the appetite system.  Weight loss is defended against and a conditioned wave (wanting/craving) is shuttled to the executive system.  If all we have is a sleepy executive to stand up to this wave – when this system collides with the modern food environment, it can be a recipe for disaster.


But there is more to the story:  your metabolism (metabolic energy).

Your metabolism is the process through which your body converts the food you eat into energy. Metabolism varies from person to person. Scientists don’t know everything about why that is. But they do know that part of that variation has to do with the composition of fat versus muscle in your body. It also varies by gender — men have faster metabolisms because they have more muscle on their bodies.  Your metabolism slows as we age — and it’s affected by our genes.

Metabolic energy occurs in three (3) main ways:

  • Resting metabolism – how many calories do you need to consume just to stay alive (does not include movement). This accounts for 50-70% of your metabolism
  • Thermic effect of food — the energy used to digest what you eat and turn it into energy. This accounts for about 10% of your metabolism
  • Physical activity — which makes up about 20-30% of your calorie burn. Purposeful exercise (like hitting the gym) is usually a very small portion of this energy expenditure. Mostly, we’re talking about the energy used to move around doing day to day activities— total daily energy expenditure (TDEE)

When you lose weight, your metabolism slows, in part through simple physics.  How many calories you burn is proportional to your weight, when you weigh less you burn less calories.  Calorie restriction also causes our bodies to compensate by slowing down your day-to-day movement.  Our total daily energy expenditure (TDEE) slows – you move less- fewer calories burned and your weight loss efforts slow – another example of a survival mechanism.  This is very unconscious, you don’t even know you are moving less – you might not pace when talking on the phone, you might not fidget as much – you don’t even know that your TDEE is lowering, it’s so subtle.

In summary, past weight loss efforts have been difficult because you are struggling with a real medical condition.  It’s mostly inherited – some peoples executive system is sleepier than others.  It’s centered in the brain – some people are more or less sensitive to hormones.  Your alarm system can be more active – triggering a wanting/craving cascade.  It’s influenced by your environment – food is always available, and highly desirable; and your metabolism might not be what it used to be.

Is this your weight loss story, yo-yo dieting, weight loss resistance (cant lose even when doing everything right), unable to follow through or do you think your metabolism is slow?  Successful long-term treatment exists.  Book an appointment with Dr. McGee to get started on your individualized treatment. 

 Watch for part 2-6 in our weight loss series where we start discussing treatments.

Part 2:  Balancing hormones – does this really factor into weight loss

Part 3:  Behaviors:  How do I wake up the sleepy executive?

Part 4:  Diet – how do I need to eat to lose weight?

Part 5:  Prescription medicines – to help the unconscious appetite system

Part 6:  Is Exercise really important – yes, but not specifically for weight loss!



Dr. Karen McGee, https://www.integratedhealthclinic.com/doctors/dr-karen-mcgee-nd/

Dr. David Machlan https://drsue.ca/2020/06/youtube-video-on-your-brain-and-weight-management-the-gatekeeper-the-go-getter-and-the-sleepy-executive/

Lumen Introduction to Physiology; February 28, 2021; https://courses.lumenlearning.com/wsu-sandbox/chapter/hunger-and-eating/

Maria Godoy, May 1, 2019, NPR; February 28, 2021, https://www.npr.org/2019/04/25/717058877/the-biology-of-weight-loss

Stephan Guyenet, pHD; The Hungry Brain, Flat Iron books, April 2017

Layne Norton; revised July 2020; Fat Loss Forever, ebook,


Dr. Karen McGee, ND

Integrated Health Clinic
Clinic number: 604-888-8325
Website, www.integratedhealthclinic.com

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