In this video I consider evolutionary explanations for the modern struggle with obesity. I describe how obesity is defined using the calculation of body mass index or BMI and consider potential problems with this simple calculation. I also discuss set point theory, energy expenditure, and the Dutch Hunger Winter of 1944-1945 and its possible role in gene expression and incidence of type-II diabetes, cardiovascular disease, and obesity.

Jason Fung on Therapeutic Fasting: https://www.youtube.com/watch?v=iatPA…

Website for the Dutch Famine Birth Cohort Study: http://www.dutchfamine.nl/index.htm

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Video Transcript

Hi, I’m Michael Corayer and this is Psych Exam Review. In previous videos I’ve talked about eating disorders, motivation for eating behavior, and hunger signaling, and so I’d like to end this series of videos related to eating and hunger by talking about obesity. Now obesity is widely acknowledged as a problem of modern societies; it’s been estimated that as much as 30% of the United States might be considered obese. So one way we can think about this common problem in modern society is to consider the evolutionary origins for something like obesity.

One way we can think about this is to consider that universally, people seem to have a preference for calorie rich foods. And if we think in evolutionary terms this makes sense because in our past famines were common. People often didn’t have enough food, and so it makes sense to crave those foods that have the most calories so you can store more energy in advance. Because you never know when a famine might be coming and so this would create a tendency to gorge in times of plenty. When you have lots of food available to you, you should eat as much as you can so that when the famine comes three months later you’re able to survive.

Of course, today, in modern industrialized society, most of us never face famine. Lean times are far less common than they used to be over the course of our millions of years of evolution and this means that our bodies have this natural inclination to store calories away, and it’s easier for us to store calories than it is for us to burn them, right? Because we want to be storing energy, because we don’t know what the future holds. Now, a related idea here is that we’re actually pretty good at dealing with famine too. That’s something that people don’t necessarily think about they think “I get hungry, I have to eat”. You know, many of us have never gone more than a few hours without eating, you know, other than maybe when we’re sleeping at night. And so many people think, you know, “if I don’t eat my hunger will just grow and grow and grow” and that’s not really the case.

So if you watch my video on hunger signaling, you might have gotten the idea that this orexigenic signal turns on and then your hunger just persists until you eat. But that’s not the case, the hunger signal can be turned off even if you don’t eat. So you get hormones like ghrelin released in the stomach, this makes you hungry, but even if you don’t eat eventually that level is going to subside. And this means that we’re actually quite capable of dealing with lean times and they’re not as bad as you might imagine them to be. If you’ve never tried an extended fast where maybe you don’t eat for a day or two days, or even longer, then you might not realize that your hunger will come and go and it’s actually not so bad. And if you’re interested in the topic of fasting I recommend some excellent lectures by Jason Fung, which you can find on YouTube, and I’ll post some links in the video description where you can find those. But let’s get back to the topic of obesity.

So what exactly do we mean when we talk about obesity? How do we define it? The main way of defining obesity is to use a calculation called BMI or body mass index and it’s actually a very simple calculation. You can do this yourself, all you need to know is your weight and your height. So your BMI is your weight in kilograms divided by your height in meters squared so that will give you a number that’s your BMI. A normal BMI is considered to be from 18.5 to about 24.9. Now it’s possible, of course, to be underweight. I mentioned in the video on eating disorders anorexia nervosa, that’s a disorder where it’s common to see BMI that’s very low you might see BMI as low as 15. But the normal range is considered 18.5 to 24.9 then when you get above that to 25 up to about 30, 29.9 that’s considered to be overweight.

And then we have the definition of obesity starting at BMI of 30 and above. So once your BMI is 30 or higher you’re considered “obese” and if it’s 40 or higher you’re considered to be “morbidly obese”. Now there are some problems with this BMI calculation when it comes to defining obesity. So the first problem is that this calculation doesn’t address where the weight is coming from. It doesn’t tell you whether this is coming from your lean muscle mass or the weight of your bones or organs, right? It’s just looking at your height and your weight and so somebody who has a very high amount of lean muscle mass; an athlete or a bodybuilder might have a very high amount of lean muscle mass and so they’re actually going to have a high BMI and they might even be considered to be obese based on their BMI, when in fact they have very low levels of body fat.

So that’s one problem with BMI and a related idea here is that the BMI calculation is not differentiated by gender, right? It’s the same equation whether you’re male or female. And yet we know that there are body composition differences between males and females. So women tend to have higher levels of body fat, men tend to have higher levels of lean muscle mass, and so what this means is because the BMI calculation doesn’t take that into account men are more likely to be considered obese by this definition. Because they’re going to weigh more for their height because they’re going to have more lean muscle mass which is gonna be heavier than their body fat. And so as a percentage of their body, their body composition is going to be more muscle mass, this is going to make them heavier and that means they’re going to be more likely to be considered obese than women who might actually have a higher level of body fat but less lean muscle mass adding to their weight.

Ok, now another idea related to obesity is called set point theory and this is the idea that our bodies have different weights that we want to maintain. So we have a certain set point for a body weight that each of us, our body is sort of working to maintain that particular weight or that particular set point. And that this is going to influence our levels of motivation for how many calories we should consume. So if somebody has a higher set point that is they’re going to be motivated to consume more calories in order to reach that particular point, whereas somebody else may happen to have a lower set point and so it might be easier for them to consume fewer calories and maintain a lower body weight. Now this also relates the idea of our metabolism and how much we burn or store the energy that’s coming in, right? And this relates to what’s called our energy expenditure.

One of the difficulties of thinking about setpoint theories, many people think of this, they say “ok, well my body has a set point. Let’s say my body wants me to burn 2,000 calories per day, well I just need to reduce my calories below that and then I will lose weight. I’ll lose, I’ll start using my stored body fat”. But unfortunately this setpoint idea is more of a range because the body is not really a closed system, is how we describe it. So it’s not the case that your body will just say “ok, I need 2,000 calories a day and that’s exactly what I will use and any more than that I’ll store and any less than that, you know, will will come out of the stored energy”.

But if you do something like reduce your calories what you see is people who have a certain energy expenditure and then they drastically reduce their calories in an attempt to lose weight and what can happen is their body’s energy expenditure can also reduce. So that means that even though they’re eating less they’re actually burning less energy and so they they don’t actually burn off any of their stored body fat. And they may you know feel more tired and hungry because they’re consuming a very small amount of calories and their body’s responding to that. So we have to keep in mind that our body is always responding to these other things and so we can’t just use a simple calculation of something like calories in or calories out. But anyway that’s the idea of set point theory.

Now another issue with it is that we don’t see drastic changes based on something like somebody’s weight loss. So somebody who goes from weighing 300 pounds down to 180 pounds, you know, we might think well this would have to have a drastic effect on their, you know, genes that are somehow setting this setpoint. And yet we don’t necessarily see that in these cases.

Ok, the last thing I’d like to talk about for hunger is the Dutch Hunger Winter. In the winter of 1944 to 1945 the Nazis blockaded Holland and what this meant is that many people starved. There was a famine lasting for about three months and researchers have looked into this famine and they were particularly interested in the infants that were born just before during or after this week brief 3-month famine. And this is known as the “Dutch famine birth cohort study” and I’ll post a link in the video description where he can read more about this study.

And one of the thing that, one of the things that the Dutch famine birth cohort study found was that the children of mothers who were pregnant during the famine, particularly those in the later trimesters, in the second and third trimester, these children when they grow up, when they grew up and became adults, they had a greater incidence of things like type-2 diabetes, cardiovascular disease, and obesity. And so this is compared to the children who were born before the famine or who were maybe born several months after the famine had ended.

So the idea was that what was happening was this this early environmental experience, right? This early exposure to famine influenced the gene expression of these children and basically what it taught them was that lean times are common, you never know when a famine might be coming, and you need to store way as much energy as possible. We refer to this as them being “thrifty” in terms of their storage of calories. Basically any extra calories you have, you want to hold on to them, you don’t want to burn them up because another famine might be coming tomorrow. And so what they do is that, this early environmental exposure in the womb, we generally think of environment as starting after birth but this is a good reminder that environment begins in the womb, right?

This exposure to famine influenced their energy expenditure, influenced their metabolism, influenced how they were storing their excess calories throughout the rest of their lives. And it’s even been suggested that perhaps there’s an effect that can be seen in their children as well. That this could even be passed on in some way through this altered gene expression of these children and then they pass this on to their offspring. And that would be an example of epigenetic change, where we have an environmental influence that actually influences gene expression, which then influences subsequent generations.

So this is another way we can think about the complicated nature of understanding something like obesity. Understanding how much of it is coming from your genes, how much is coming from your environment, including these extreme early environmental experiences like experiencing a famine while you’re in the womb, and we can see just how complicated trying to understand something like obesity is. Ok, well I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!