Evolutionary Psychology 101: Why Diets Fail

by Angela (Oh She Glows) on September 21, 2009

I am often asked if there were any parts of my training in social psychology that were influential on the way that I now view my road to health.

I always think back to a course that I took during my 3rd year of my undergraduate program called Evolutionary Psychology. This course was in part responsible for the gradual shift in my disordered eating behaviours. It helped me view my body in a new light and to appreciate why certain frustrating behaviours (like binging and over-eating) were happening.

This is one of my favourite books of all time:


And trust me, I cannot say this about 99% of the textbooks I purchased during my undergrad and grad school careers. The book is short, clear, concise, and can be easily understood by someone without psychology training.

Given that the back-to-school season is upon us, I thought it would fun to host a series of educational workshops about our health, pulling from interesting topics that I have covered in some of my classes.

What is Evolutionary Psychology?

Evolutionary Psychology is a division of psychology that focuses on how our traits and behaviours evolve because of natural selection. Natural selection is the term coined by Darwin, to describe the process by which adaptive traits are ‘selected for’ (i.e., continue to reproduce in a species) while maladaptive traits (i.e., traits/behaviours that do not help a species survive) die out.

My Evolutionary Psychology course was one of my favourite courses that I have taken over the 7 years of my training.

My instructor was everything you would dream an instructor of evolutionary psychology would be: Extremely quirky, tall, lanky, overgrown grey hair, and extremely off-beat yet highly intelligent and amusing. One class he even brought his pet Parokeet to teach a lecture with him! Not surprisingly, his Parokeet could speak many words and was very smart.

To start off, I would like to focus on Chapter 10: Health.


Not surprisingly, this was my favourite chapter in the entire book. I have read it many times over. It was also partly responsible for the slow and gradual change in my road to health

Why Diets Fail

Then + Now:

  • Our ancestors were generally quite fit, lean, and were capable of remarkable feats of athleticism. Contrast this with our current society, and you will see that over half of men and women are either overweight or obese.
  • Despite the fact that the diet industry is growing and growing each year, 95% of all diets fail, with most individuals either not loosing weight or gaining back the weight they lost within 1 year.

Why do diets fail?

Adult Human Body Weight Is Remarkably Stable.

  • Generally speaking, adult human body weight is very stable! The body strives to maintain its’ current weight.
  • Our weight tends to stay quite stable over a period of time, even despite the fact that what we eat daily tends to vary greatly from day to day.
  • The mechanism that keeps our weight constant, despite these daily fluctuations, is also the same thing that makes it hard for people to lose weight.

Body Weight is maintained by a feedback system with a setpoint!

  • A setpoint is what I like to call a body’s happy weight. It is the point where your weight naturally tends to fall when you aren’t giving a great deal of effort via exercise and diet to lose weight.
  • For example, rats and humans who have been starved below their setpoint will eat more food once it is readily available until they regain to the setpoint weight.
  • When someone is eating above their set point weight, it is common for the body to compensate by eating less food to return to the setpoint. You probably have experienced this over the holidays when you have a few days or weeks of over-indulging and you find that afterward all you crave are salads and fruit! This is your bodies way of returning you to its setpoint weight.
  • This setpoint regulation system operates at a subconscious level. In other words, it will operate without us ever having to give it any thought. That is, unless we start to mess with the system by dieting and obsessing!
  • The books authors, Gaulin & McBurney, say that our bodies regulation system is a very adaptive mechanism and we take it for granted. If we didn’t have this natural tendency to eat more when we need to gain weight or to eat less when we need to return to our setpoint, we would either waste away or eat until we are obese.

What happens when going on a diet:

  • When people go on a diet, they often find that their weight drops at first, but then the weight loss plateaus.
  • Our bodies respond to a diet by first dropping our metabolic rate. The result is that we now burn fewer calories than we did before = NOT GOOD!
  • When our bodies drop the metabolic rate, this is a signal that our bodies are resisting weight loss. Our bodies do not want to be in a state of imbalance. All it wants to do is maintain its weight at the set point.
  • It is very frustrating because even though we are eating much less than we did prior to the diet, we are still not losing weight.
  • We are hungry all. the. time.
  • If that wasn’t bad enough, when we do eat more, our weight will often climb higher than it was previously because of our now reduced metabolic rate.
  • This is an evolutionary adaptation that permitted our ancestors to survive during long periods of famine. When our bodies think it is in a famine, the metabolic rate plummets and we function and maintain our weight even though we aren’t eating a fraction of what we used to. The result is an often irritable and unhappy dieter confused and desperate.

As a result of these evolutionary mechanisms to maintain our weight, it is very hard to go on a reduced-calorie diet and lose weight successfully for the long-term.

However, while the odds are stacked against individuals looking to lose weight, there is hope.

In the next post of this series, I will tell you one thing that you can do to overcome this frustrating setpoint system and be successful in healthy weight loss and maintenance.


Have you experienced this frustration when trying to lose weight?

Do you think your body has a setpoint weight? Why or why not?

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{ 48 comments… read them below or add one }

Michelle September 21, 2009 at 11:52 am

What a fantastic post! I’m part way through my Sports psych degree and I wish my university offered an Evolutionary psych course! I am excited to read your next post in these series!

Angela, your blog is amazing!


Bree September 21, 2009 at 6:19 pm

What school are you going to? I’m 3/4 of the way through my sport psych degree. :-)



Molly September 21, 2009 at 11:36 pm

Hi Angela!

I’ve just discovered your blog today, but 1st, I’m at the beginning of the “healthy journey”, and still struggling, don’t know where to start- but 2nd, I took Ev.Psych as an undergrad and LOVED IT. It was the only text book I can honestly say I’ve read cover to cover and enjoyed. I wish I wouldn’t have sold it back! Thanks again for your blog. I’ll be following it now!


Nikki T September 21, 2009 at 11:53 am

I wish my co-workers would understand this whole diet thing…and why it doesn’t work!
I will continue to try and get them out of the rut!

PS- I picked up some of those coconut popcicles at Superstore yesterday…YUM!


Madeline @ Greens and Jeans September 21, 2009 at 11:55 am

I was a human biology major and I truly believe that every single person has a weight that their body is happy at. If anyone has lost TOO much weight, they know how hard this is to maintain because your body doesn’t want to be that small! If you have ever packed on a few pounds, you probably feel uncomfortable, and not just because your clothes are a little tight, that is your body telling you that it isn’t happy! The human body is an amazing thing!


Angela (Oh She Glows) September 21, 2009 at 12:14 pm

I fully 100% agree with this.


Anne Marie @ new weigh of life September 21, 2009 at 12:08 pm

Very interesting!! I’m taking a psychology course (class started today), and I can’t wait to see what I learn!


Pam September 21, 2009 at 12:17 pm

I think our bodies do have a set weight where it likes to be. The problem I think is actually listening to your body. We have totally lost touch with what it feels like to be full and to listen to our cravings. I really believe that our bodies crave what we’re lacking. I think it takes A LOT of practice to be able to recognize those signs. I’m still working on it!


Chloe September 21, 2009 at 12:24 pm

Interesting post Angela! I know my body has a set point, and when I add a little more effort I may lose a couple of pounds, but I always hover around the same numbers. The key is to stay that way throughout my life!

It’s also interesting to note that our original diets, thousands of years ago, had very simple, basic foods. Very little sugar, no preservatives or additives, or HFCS. Now we’re bombarded with all sorts of crap and it takes an effort to find what our bodies need.


Mellissa September 21, 2009 at 12:28 pm

I know my body has a setpoint weight, I have been within a few pounds of this for years! I have a really good friend who has yo-yo dieted for years and has been a Size 0 to a Size 16 and always strives to get back to that Size 0 and we have conversation after conversation about just being healthy and eating the right foods and working out in a balance. She needs to read this post!


Haleigh September 21, 2009 at 12:30 pm

The human body is very complex but I believe that if you listen to it, then it will tell you what it wants/needs. I agree completely about the human body having a setpoint weight. It is so hard for me to maintain something lower than my “setpoint” and when I am above it, then my body feels uncomfortable and I am always full.

Great post Angela! Your blog is just amazing.


Sarah @ The Foodie Diaries September 21, 2009 at 12:30 pm

Angela, amazing post! I can’t wait to read the rest of your educational series bc I am in serious back to school withdrawal! I 100% believe in the set point theory, and know from my personal attempts to have a healthy, mutually beneficial relationship with food that the body knows itself and its needs best.



Runeatrepeat September 21, 2009 at 12:34 pm

This is very similar to what my RD told me. The human body is very smart, it will do whatever it can to get to keep from starving if you are denying yourself food.


Angela (Oh She Glows) September 21, 2009 at 1:03 pm

My binges never fully stopped until I stopped depriving myself. Interesting concept, no?


Whitney @ Lettuce Love September 21, 2009 at 12:36 pm

This was a wonderful post! I love learning about why we do the things that we do. I agree that we all have a weight that our body is the most comfortable and efficient. I have noticed when I gain a little weight from weekend parties or the holidays, it only takes a week or so to get back to where I was because my body just wants to be at “my” weight. I am looking forward to all of you educational posts –can’t wait!


kristi (sweet cheeks) September 21, 2009 at 12:36 pm

I am very interesting in this series…can’t wait to read the next post on it! Great job Angela! :)


Hallie September 21, 2009 at 12:38 pm

Great post! I’m really interested in the next part because I do think my body has a set point…and I don’t like what it is! Maybe some day I’ll accept it, but I really want to be about 10-15 pounds below what my body seems to always go to. It’s not like I’m trying to become a skeleton though, so I guess I just feel like I can retrain my body to get to a new set point….eventually. It’s hard though. Really hard.


The Big Blue Dog September 21, 2009 at 12:41 pm

Great post. I love learning about Human Evolution. It is so interesting to me to see where we have come from and where we are going. We can learn so much from the past.

The idea of a setpoint weight is very interesting!! It makes a lot of sense, there isn’t an ideal one-size-fits-all.

Thanks for the educational info! Looking forward to the next in the series!


mmclaughlin September 21, 2009 at 12:41 pm

Great post!! I can’t wait to hear more about it, thanks for sharing! :)


Kristin (Kristins Nibbles) September 21, 2009 at 12:47 pm

This is incredibly interesting! Thanks for posting it!



Lindsay September 21, 2009 at 12:54 pm

How funny, I took that course in college as well, and we used the same text book, LOOOVED it. Don’t remember the health chapter though, gonna go back and take a look at it myself. Great post!


Angela (Oh She Glows) September 21, 2009 at 1:04 pm

Wow that’s neat! I love this book so much.


Jessica September 21, 2009 at 1:42 pm

good post… REALLY looking forward to the next one because I’m struggling with the last few pounds that i feel are above my setpoint weight. now that is with my amount of muscle. if i can gain muscle and reduce fat, cool.


Kath September 21, 2009 at 1:46 pm

LOVE this topic – and this post!! Get simplification Ange! Can’t wait for the next lesson :)


Marina September 21, 2009 at 1:51 pm

I love this post, very interesting topic!
I think I have some kind of ideal weight that I’ve been around for some time, but I seem to want to go lower…maybe. My scale is really not working very well, so I don’t know even if I’m maybe bellow that weight which is healthy for me.


Jessica September 21, 2009 at 2:26 pm

I certainly have experience with this. In the past I have been able keep myself 5-10 lbs lower then my “setpoint” weight but I am miserable when I try to do it!!!!

It has been an adjustment for me to be “comfortable” being at a weight that is a bit higher then my lowest weight (which I reached after losing 50 lbs.) That (too) low weight felt like such an accomplishment – I wanted to stay there. But, like I said, it was miserable to keep myself there, it was lower then where my body wants to be. I am still working on learning to trust my body – I am getting there.


Kiersten September 21, 2009 at 2:30 pm

Thanks for the info Angela. I never realized until now that you were a psychology major. I am majoring in psychology too (thinking about going the Health Psychology route). I don’t know if we are offered any courses on Evolutionary Psych, but it sounds very interesting. I may have to check that book out!


RunToTheFinish September 21, 2009 at 2:31 pm

fantastic post, I actually may have to go read that book now. i’m always intrigued to learn more about these things


Claire September 21, 2009 at 2:32 pm

This is an awesome topic.I’m always learning with your posts.I can’t wait for the rest on this:-) cc


Bec September 21, 2009 at 2:40 pm

great post, its so true you have to change you lifestyle not go on a diet to lose and maintian weight loss


Lindsey (Mrs. LC) September 21, 2009 at 3:00 pm

So interesting. I absolutely cannot wait for the rest of this series, how fun!

I definitely agree that our bodies have a setpoint for our weights. However, I feel like there are so many things in today’s culture that may make it hard for one to find their setpoint. The biggest thing is something that is our own fault – the consumerism “gimme now, I want it now” attitude. People want a healthy lifestyle now, they want to lose weight now, they want that order of fries now, now now now! However, I do think there are many other aspects of today’s society that hinder people from finding and staying around their setpoint weight. So many people (and students) have jobs behind a desk, where they are sedentary most of the day. Plus, medication – as part of the “gimme now” culture, we want medicine for every ache and pain that pops up. Beyond aches and pains though, are actual problems (asthma being one), so we go on other medications like allergy meds, asthma medicine, birth control, etc. With many different medications (obvs. not all), a side effect is weight gain.

Sorry for writing a book, I was actually just thinking about all of this the other day! I just think overall, so many people’s lifestyles and cultural influence are stacked against how our bodies were originally made.


Rebekah September 21, 2009 at 3:05 pm

Very interesting post! Thank you!


Cait (Cait's Plate) September 21, 2009 at 4:09 pm

Awesome post as always Angela!!


Kristen September 21, 2009 at 4:12 pm

What a great post with a cliffhanger ending!! I am at the edge of my seat waiting for the next one.

I love textbooks that are actually good to read as well, I wish we lived in a world where that was always the case. Looks like that one might be worth picking up though!


Heather Dawn September 21, 2009 at 4:13 pm

Awesome post! I cant wait to read more :) I am currently in a fitness tech program to become a personal trainer. Its amazing how smart our bodies really are! Its getting past the psychological aspect of wanting to lose weight or thinking you need to that is the difficult part.

I noticed that I will lose weight when I really dont think about it. I remember about 2 years ago I decided that I was really going to enjoy the holidays and not worry about indulging at all!! I also cut back on exercising as I was too busy. Interesting enough, I actually lost weight over the holidays! This may or may not have been a loss of muscle tone as well :( However, my body felt good. I dont think I overate during that time!

The only problem now is how do I get back to that mindset? I eventually fell back in to some of my unhealthy habits and the stress that goes along with it.


Alex September 21, 2009 at 4:37 pm

GAWD I love these hot topics!!!

I was a psych major too and although I never took any evolutionary psych classes, the subject was definitely touched upon, and I’ve come across it indepently in my own reading too. It’s a subject that totally fascinated me, and one that provides a lot of answers related to most of our biological drives (eating, sleeping, sex, etc).

I definitely know I have a setpoint weight, and it’s where I’ve been for the past two years or so, despite living in different countries (and thus changing my diet based on what was available), drastically changing exercise patterns, etc. My setpoint weight gradually appeared when I stopped dieting, exercising fanatically, and worrying so much about the scale number, ironically.

I couldn’t be happier about it! The best part about a healthy setpoint weight is that it’s so darn low-maintenance! So long as I’m being reasonable (and being reasonable INCLUDES natural fluctuations!), it’s pretty easy to stay here!


Jessica @ How Sweet It Is September 21, 2009 at 4:40 pm

Great informative post! :)


Tay September 21, 2009 at 5:36 pm

I’ve read about setpoints before, and the fact that our body gets comfortable and creates a new setpoint if we’re overweight. So if you’ve been 180 for a long time, then your body becomes accustomed and makes that it’s “new” setpoint. And that makes it even HARDER to lose weight, because your body fights to get back up to that weight!

Thanks for you information – it’s very informative and all makes sense!


Kate G. September 21, 2009 at 5:42 pm

THANK YOU for this post. it makes me SO excited to start school again and begin studying nutrition :) i love this kind of stuff which is why i am pursuing a degree in dietetics.

very excited to read the upcoming posts!

Kate G.


Averie (LoveVeggiesAndYoga) September 21, 2009 at 5:42 pm

Thanks for the thoughtful post. As a former psychology major and grad student, I appreciate a little “books smarts” kind of info going on in your post today :)

I do think to a certain point your body has a set point, a place it likes to weigh. However, under extreme conditions, it can go below this point…but when you’re given access to ample calories again, it will usually bounce back to it’s comfort range. Think the contestants on the show Survivor, or a more gruesome tale, concentration camp victims. Once back in the real world, most people will gain their weight back I think. Sort of reinforcing the set point theory. However, I believe that by paying close attention to foods and food allergies/intolerances (most people think they dont have any but quite possibly they do) you can actually get to the bottom of many diet challenges. Sorry to ramble :)


katie September 21, 2009 at 7:24 pm

Can you buy this book in a regular bookstore??? Thanks!


Angela (Oh She Glows) September 21, 2009 at 7:30 pm

You can buy it on Amazon, keep in mind it is VERY pricey since it is a textbook. They loved to hike up the price for texts…ugh



maria September 21, 2009 at 8:17 pm

This was great. I’ve always been unsure about the set point theory, and to be honest I am still not 100 percent sold, but I have noticed that since I’ve gotten closer to my goal weight it is sooooo much harder to lose and it requires almost perfection on my part.


Jess (Fit Chick in the City) September 21, 2009 at 9:44 pm

Love this series of posts! Yes, I believe my body has a set point. There’s a weight that is really easy for me to maintain no matter what my exercise level is at that point in time. I gain weight when, I’m honestly just eating too much.


Kerry September 21, 2009 at 9:46 pm

Fantastic post, and I look forward to more.

Yes, I definitely feel we have a set point, although I think that set point can be changed as long as it is within a healthy range for our bodies. A complex topic for sure!


Jolene September 21, 2009 at 11:10 pm

I love psychology classes!!! I have taken about 22, but missed that one :-( I don’t think my university offers it, but I am going to check!!


natalie September 22, 2009 at 10:30 am

This is great. That is exactly what I have done in the past and that is exactly what has happened. I can’t wait to read the rest.


Jenn Eats Nutritiously Now September 22, 2009 at 3:13 pm

This is such an interesting post. So what is it that makes us eat beyond our set point? Does that mean we’re not listening to our bodies well enough, or are our bodies not telling us when we need to stop?


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