4 Key Questions for Understanding the Obesity Epidemic


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In my last post here at OrganicFitness.com I talked about the pyramid model and how important it is to build a solid foundation to support our ideas, thoughts, and conclusions upon. I discussed how this pyramid concept can be used to critically analyze study results, media reports, conventional wisdom, etc. and how evolution, history, science, and experience help us build a solid structure. In this article I’m going to show why it’s so essential to begin by establishing a robust base and how we can use the pyramid principles to make sense of a seemingly complicated topic, The Obesity Epidemic. I realise that most of my articles on the subject can be a bit lengthy and sometimes technical, and I therefore thought it was time to summarize (as briefly as possible) the essentials. Although my articles on overweight, obesity, and weight loss can seem very different from each other, they are all based upon the same fundamental principles.

As those who’ve been reading this blog for some time know, body fat regulation is one of the subjects I’ve written most about. This interest stems from a combination of the following factors:

  • The primary goal of most of my clients over the years has been to lose weight.
  • I study nutrition.
  • Overweight and obesity are closely linked to overall health.
  • The obesity epidemic has quickly become one of the greatest health challenges humans have ever faced; meaning that there are a lot of people out there struggling with their weight.

1) At the most basic level, what causes obesity?

Without a doubt, I think the best way to begin investigating this question is to look at human evolution and the history and epidemiology of the obesity epidemic. What do we know?

  • Obesity is unheard of in hunter-gatherer populations and primitive cultures eating traditional diets. This is true even when food is abundant. The transition from eating traditional, whole food to eating a western-type diet is associated with fat gain and declining health status. (1,2,3,4,5)
  • Worldwide obesity rates have increased dramatically over the last 30 years (6).
  • If we compare the human species to other animals and look at people living in an ancestral natural environment, it becomes clear that leanness is the natural state of human beings.

While these observations, at least at first sight, don’t give us any definitive answers to the initial question, they do tell us one very important thing: There’s something about the modern environment that is driving the obesity epidemic. This is something most people intuitively know, but it’s often forgotten. If we don’t include this underlying premise and instead jump right in by looking at specific hypotheses of obesity, we don’t really know if we’re looking in the right place.

There were definitely obese people around prior to the last couple of centuries, but if we look at the obesity epidemic from the perspective of the ancestral natural environment vs. the modern environment it becomes clear that obesity is primarily a disease of civilization.

If we acknowledge that the underlying cause of the obesity epidemic is a gene-environment mismatch and understand that all hypotheses of obesity must be consistent with this idea, we can use this an underlying structure and start building up towards the specific causes of fat gain.

2) In terms of human health, what are the primary differences between the modern “obesogenic environment” and the environment of non-obese populations?

This is the natural next step when we have established that obesity is a disease of civilization. There’s definitely plenty of variability here, but there are some lifestyle/environmental factors that seem to play an especially important role:

  • Physical activity
  • Sun exposure
  • Hygiene, microbial exposures, and pharmaceutical use
  • Nutrition
  • Stress
  • Sleep
  • Exposure to pollutants

3) Which of these factors are most important in terms of the obesity epidemic?

This is the natural next question after we’ve established 7 possible factors that could play an important role in the obesity epidemic. We’re now working our way up the pyramid towards the more specific ideas and hypotheses.

The scientific literature supports a role for all 7 items, and taking care of all of these things is a good idea if you want to be as healthy and lean as possible. However, when it comes to body fat regulation, there’s definitely a varying degree of importance (Also largely depends on the individual).

First, I’d like to remove 3 items for the list; exposure to pollutants, stress, and sun exposure. Not because I don’t think they are important when it comes to human health, but because the scientific literature shows that they are not the primary drivers of the obesity epidemic. They definitely play a role (for some more than others), but it’s fairly small compared to the other items on the list. That leaves us with sleep, physical activity, diet, and hygiene, microbial exposures, and pharmaceutical use. All of these factors play a causal role in the obesity epidemic. However, they are definitely not all equally as important.

4) When it comes to these 4 factors, what are the major differences between obese and non-obese populations, and through which mechanisms does this mismatch drive the obesity epidemic?

One essential thing we have to remember is that all of the mechanisms have to be consistent with our basic idea. This means that all of our ideas and hypotheses at this point have to be rooted in the fact that obesity results from a mismatch between our ancient physiology and the modern diet and lifestyle. Having this underlying premise is immensely important as it provides a framework and helps us narrow our focus.

If we compare the two most extreme ends of the spectrum, a typical hunter-gather population (e.g., Native Inuits living a traditional lifestyle, no obesity) and a U.S. population (e.g., urban dwellers, ~30% obesity), it’s clear that the environment and lifestyle are very different. These differences get smaller as we start comparing industrialized nations with varying obesity prevalence, but they are still present. Also, genetics play a role (More on this in the end of the post).



No overweight in Melanesian islanders eating an ancestral diet. Studies shows that the human energy homeostasis system functions well when we eat these types of foods. Photo source

Core concepts: The most important player. As body fat mass is biologically regulated, simply telling someone to eat less is not very good weight loss advice. Yes, we do have to decrease our energy intake and/or increase our energy expenditure to lose weight, but this happens naturally if we understand how to work with our bodies. The systems in our body that regulate appetite, energy intake, and fat storage on a long term basis evolved to deal with minimally processed whole food, like those hunter-gatherers and primitive traditional populations eat/ate. Highly processed westernized food overwhelms the reward center in the brain, alters the gut microbiota, and has several other undesirable effects that cause us to eventually store more fat. Essentially, there are major differences between the foods we are adapted to eat and those that make up most of the western diet.

3 selected articles on diet and body fat regulation
Why the Traditional Approach to Weight Loss Comes Up Short
Do Carbohydrates Make You Fat?
Evolution: The Basis for Understanding Human Nutrition

Physical activity

Core concepts: Contrary to popular belief, physical activity expenditure has not declined over the same period that obesity rates have increased dramatically (1). Since body fat mass is homeostatically regulated, it’s no surprise that the scientific literature shows that exercise is usually not very effective for weight loss. However, physical activity definitely plays a role in preventing obesity, insulin resistance, and leptin resistance, and a minority responds to exercise by losing “a lot” of weight (probably related to the metabolic effects). Essentially, the systematic displacement from a very physically active lifestyle in a natural outdoor environment to a sedentary indoor lifestyle is one of the driving forces behind the obesity epidemic.

3 selected articles on physical activity and body fat regulation
Does Exercise Make You Lose Weight? Part 6: Summary, Discussion, and Conclusions
How Being Overweight Can Make You Fatigued and Inactive
Exercise or Training? A Question That Determines Your Workout Results

Hygiene, microbial exposures, and pharmaceutical use

Core concepts: The gut microbiome – the collective genomes of all the microbes that live in the GI tract – influences metabolism and body fat regulation. The modern, western lifestyle perturbs the ecosystems that live in and on our bodies.

3 selected articles on the human microbiome and body fat regulation
Genetics of the 21st Century: Microbes Affect Disease Susceptibility, Body Weight, and Ability to Build Muscle
We Are 90% Microbe and 10% Human: Can We Lose Weight by Boosting Good Bacteria with Probiotics and Prebiotics?
Is the Obesity Epidemic in the U.S. Partly Driven by Chronic Exposures to Low-Residue Antibiotics in the Food Chain?


Core concepts: “The adverse impact of sleep deprivation on appetite regulation is likely to be driven by increased activity in neuronal populations expressing the excitatory peptides orexins that promote both waking and feeding. Consistent with the laboratory evidence, multiple epidemiologic studies have shown an association between short sleep and higher body mass index after controlling for a variety of possible confounders” (1).

A quick word on obesity and genetics

We know that genetics play a role in obesity! However, we also know that obesity to a great extent is a disorder of the modern civilization. This makes it pretty clear to me that epigenetics and the second genome are the keys to understanding genetics of obesity.

As I’ve repeatedly talked about, the western lifestyle is a master manipulator of the second genome. In terms of our human genome, we know that environmental factors impact gene expression and that these changes can be passed on to future generations. What does this mean? It means that one of the key reasons we’ve seen steady rising obesity rates over the last several decades is that our diet and lifestyle have a significant impact on gene expression (both the human genome and the human microbiome) and the structure of the human microbiome – changes that can be passed on to future generations. In other words, unless we manage to stop the development we’re now seeing around the world (e.g., sedentary lifestyles, highly processed diets), the rates of diseases of civilization, such as obesity, will likely only continue to increase.


To find the true causes of the obesity epidemic we have to look at human health from an evolutionary point of view and understand how the environment and lifestyle of obese populations differ from that of lean populations. If we had jumped right in at question number 4 (trying to jump in at the top of the pyramid), we wouldn’t know if we were looking in the right place.  However, when we have a solid underlying foundation, we understand that all of the mechanisms we propose in each step have to be rooted in our previous conclusions. 


  1. Your the man Eirik. The way you’ve broken down a complex subject is very impressive


  1. […] all good hypotheses and conclusions have to be rooted in a robust underlying structure. Just like jumping in with specific hypotheses of obesity is premature if we don’t have a solid foundation to build our ideas upon, we can’t really understand […]

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