I recently read The Book on Heat: The Science of Heat for Weight Loss, Performance and Health by Brad Pilon. It altered a view of mine that I’ve held for decades related to diet and exercise.
My seasonal view was that during the spring and summer, I was outside more. I was more active. That activity supported a leaner body. Then when colder weather hit, I would be indoors more. A combination of inactivity paired with the increased calories I was consuming during the warmer active months would result in a fat gain. In my model, body composition gains from exercise happen in the short term, but eventually, the body increases appetite to match the increased energy demands. Then winter arrives, we head inside, and activity drops, but our appetite stays elevated long enough to reverse our summer physique gains.
I now think I was wrong.
The Book on Heat makes the case that warmer temperatures reduce appetite. So summer leanness is primarily a result of heat, not activity. This makes sense. I’ve been in hot muggy environments before and I don’t feel like eating much. Plus the foods I gravitate towards, tend to be lighter with fewer calories.
What about exercise? What if the leanness from exercise is more a result of the ambient temperature than the workload itself?
By sending signals that the environment is warm, the brain begins to recognize the expensive energic cost of carrying excess fat, and appetite is reduced.
Cold is doing the opposite. It increases appetite.
The book goes much deeper into the relationship between temperature and appetite with references to decades of studies supporting the thesis. Some other interesting items from the book:
- Insulin sensitivity and our ability to store fat improves in colder weather. Warmer temperatures have the opposite effect.
- Colder temperatures stimulate appetite not only due to the thermic effects of eating more but also the insulation benefits body fat provides. Protection against the elements and heat loss.
- When adjusted for subcutaneous fat levels, women have a greater surface area than men, and thus feel colder at the same temperature. They require higher body fat levels to feel comfortable in the same environment.
What about cold exposure? I have lots of posts on this site related to cold exposure and the benefits I’ve experienced. And although initially, I thought cold exposure would benefit fat loss, I became a skeptic, but I didn’t know the reasons. From my 2018 post Fat Loss Cheatsheet: What Works and What Doesn’t (for me):
Sorry, Ray Cronise, but my experience is that cold exposure is almost worthless for fat loss. I am still a fan of cold exposure for building resiliency, but not for leaning out. As others have pointed out, cold exposure makes you hungry. Indirectly, however, if cold exposure toughens you up to the point you are more comfortable with hunger then it could help. I remain unconvinced it would have anything but a minor role in fat loss.
Thanks to The Book on Heat, I now know why. In addition to everything mentioned above, I learned that using cold exposure to build BAT (brown adipose tissue) to generate heat and help you get lean may be a shortsighted strategy.
There it is. Cold triggers BAT. BAT generates heat to protect the lean body in the short term. The body responds to the BAT as a signal to spike your appetite. I still plan to take cold showers as this exposure is too short to matter. However, I will think twice before spending hours outside in cold weather without a jacket.
How can cold be a factor in the obesity crisis? Pilon defines “cold” based on his research as “cold to the naked body”. This would mean offices and other air-conditioned environments are appetite-stimulating. Living most of our lives inside in comfortable/cool temperatures is slowly making us heavy.
…it would be highly advantageous to stay warm when you are dieting, as dieting and cold are both signals to eat more.
This also explains why I find longer fasts of 3-5 days easier in the middle of the summer and nearly impossible during the winter.
Visit TheBookOnHeat.com for more info. The book is also available on Amazon.
Connecting the Dots
In 2018, I mentioned that my advice for big guys to just lift and forget cardio was wrong. My thinking then was that the cardio would spike their appetite and although they’d see progress initially, eventually the initial losses would be replaced with extra hunger and weight regain.
But, what I learned from trainers is that the big guys respond well to cardio. Now in light of Pilon’s book, I see cardio as a thermal stress that will downregulate appetite. This wasn’t my experience when I was a runner, but I was also lean, lanky, and outdoors. I was able to diffuse body heat from exercise easily.
If I had weight to lose, I’d be testing longer durations of “cardio” that caused me to get warm. Frequent brisk walks in the sun as opposed to biking for 20 minutes in an air-conditioned gym.
I can probably think of 10 stories from my own life that seem clearer now in the light of what I learned in The Book on Heat, but since this post is getting long, I’ll just share this one.
When I worked an office job in San Diego many years ago, I recall a female manager who always complained that the office was too cold. She wore sweaters or jackets. She was lean. Then she kept making trips to the front desk where there was a huge bowl of M&M candies. She probably gained 30 pounds in a year. Was she unconsciously eating to stay warm? Until I read this book, I didn’t think about this story. She stopped eating M&Ms after the weight gain. She also stopped complaining about the cold office.