We are constantly bombarded with the latest scientific discoveries. One article describes a set of scientific results. Then three months later, another article gives opposite results. What do you do?


With these contradictory results, it would be easy to give up on science. But I’m not sure science is to blame. Each study gives us a clue to the final answer. Here are a few thoughts to shed light on these contradictions and teach us to take a bird's-eye view of the issues at play.


Air Conditioning Causes Obesity

In a 2006 study, David Allison and colleagues described a correlation between obesity and air conditioning use. People in warmer climates who used air conditioning were heavier than those who did not. In the southern United States, the percentage of homes with air conditioning increased from 37 percent in 1978 to 70 percent in 1997. The rates of obesity rose at a similar rate.


The media headlines claiming air conditioning was making us fat exploded. Articles pointed to the lack of obesity in old Italian villages without air conditioning. It seemed we found a solution to this large problem (pun intended).


But Wait: Cold Burns More Calories

Before you throw your air conditioner out the window, let me explain the next theory. Ray Cronise, a former NASA scientist, wondered how Michael Phelps could eat 12,000 calories a day without becoming obese. He hypothesized that it was because Phelps spent three hours a day in cold water, so his body had to burn more calories to keep him warm. If this hypothesis were true, it would suggest we could burn more calories by exposing ourselves to cold.


Does cold cause more calorie burn?


Cronise tested it out on himself by taking cold showers, walking three miles in the winter cold with just a t-shirt, and sleeping without covers. He lost 27 pounds in his three-month experiment. (For a more eloquent explanation, see Tim Ferriss’ 4 Hour Body.)


Which theory is right? Let me save my answer for the end. In the meantime, stick with me as I bring up another confusing question.


Intermittent Fasting

Bodybuilding-style diets where people eat six meals a day have been popular for years. The theory is that by eating small meals, the body’s insulin never spikes and we don’t store as much fat. Many people have been successful, and this type of diet is still prescribed and practiced today.


On the other hand, intermittent fasting has also become popular. (Ori Hofmekler wrote about this topic quite a while ago.) In this diet, you refrain from eating for a specified amount of time and limit your daily meal window to a few hours. This theory is related to our animal ancestry where we hunted for hours and then binged when we were successful on the hunt. You will lose fat in this diet because you are in fat-burning mode for most of the day. Many people report exciting results.


Individual Differences

Each person’s metabolism and digestion is different. Some of us have a gene that produces more alpha-amylase, which breaks down starches when they enter our mouth. These lucky individuals can eat more carbohydrates and not gain weight. Individual differences continue down the digestive tract. We also have different gut biomes, so we each digest our food differently.


The process also changes depending on what we eat. Vegetarians and carnivores have different biomes. If they were to switch their meat eating preferences, their bodies would adapt by changing the gut biome.


Well, if you heard it at #CrossFit it must be true.

Posted by Casual on Saturday, October 17, 2015


I wrote an article explaining why you are not normal and that is a good thing. Think about two people approaching a deadlift. The person with a short torso and long arms will have a much easier time than a person with T. rex arms. But the person with T. rex arms will be great at bench pressing. Each person has some advantage over the other.


The bottom line is that there might not be one right answer for everyone, but there is an answer that is right for you.


Multiple Contributing Factors

We often look for simple solutions to our problems. Studies tend to isolate one causal mechanism. It is more likely that there are multiple contributing causes. In the deadlift, we can think of many factors that might affect our performance, such as muscle weaknesses, imbalances, tightness, previous injuries, and body structure.


So why would we think the cure for obesity is as simple as turning off air conditioning or eating a certain type of food? There are multiple causal mechanisms that work together.


"We have improved our lives with air conditioning and other conveniences. These changes could be the causal factors, either individually, or more likely, in combination."

A common mantra from research design class is, “Correlation does not equal causation.” I often use the example of religious institutions and crime. As the number of religious institutions in a city increases, the number of crimes also rises. Does this mean participating in religion causes more people to become criminals? Or do religious institutions come to cities to reduce crime? It is probably neither. Rather, larger cities have more crime and more religious institutions. These two variables are only related because of the city’s size.


Getting a Clue From Science

The same concept holds for the air conditioning theory. We have improved our lives with air conditioning and other conveniences. These changes could be the causal factors, either individually, or more likely, in combination.


My take on the air conditioning question is that our bodies are not exposed to temperature variability. If we live with our thermostat at a constant temperature, our bodies may not know the seasonal changes. It might be good for us to expose ourselves to more extreme temperatures.


So what about the theory that cold burns more calories? At the cellular level, exposing your body to cold leads to the growth of brown adipose tissue (BAT) fat cells. These fat cells regulate temperature and help the body to burn more calories in cold.  


Currently, I practice sleeping without covers and walking in the cold without a jacket. In the summer, I try to leave the air conditioning off. I may be on the wrong path, but I base my decisions on clues from our current scientific knowledge base.


Take a Bird's Eye View

By taking a bird's-eye view of these studies, we can make more sense of possible answers. But we always have to live with uncertainty. Studies may point us in opposite directions at times, so we need to see what puzzle pieces we have and how they fit together. Some puzzles, like nutrition, have many complicated pieces that don’t always fit. Coaching a deadlift is much simpler.


As I receive more information, I might have to adjust. One study does not lead to a complete change in my behavior. Rather, it forces me to fit this new piece into my existing knowledge. Take a step back and try to see the whole puzzle. Gather as many pieces as possible to determine how it all fits together.


You'll also enjoy:



1. Ferriss, Timothy. The 4 Hour Body: An Uncommon Guide to Rapid Fat Loss, Incredible Sex and Becoming Superhuman. 1st Edition. New York: Harmony, 2010.

2. Hofmekler, Ori, Harvey Diamond, and Udo Erasmus. The Warrior Diet: Switch on Your Biological Powerhouse For High Energy, Explosive Strength, and a Leaner, Harder Body. 2 Rev Exp edition. Berkeley, Calif: Blue Snake Books, 2007.

3. Keith, S. W., D. T. Redden, P. T. Katzmarzyk, M. M. Boggiano, E. C. Hanlon, R. M. Benca, D. Ruden, et al. “Putative Contributors to the Secular Increase in Obesity: Exploring the Roads Less Traveled.” International Journal of Obesity 30, no. 11 (June 27, 2006): 1585–94. doi:10.1038/sj.ijo.0803326.


Photo courtesy of Shutterstock.

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