How Does Being Cold Affect Appetite and Fat Burning?
This Week’s Research Highlight
Temperature’s Hidden Role in Weight Regulation
The latest statistics tell a dismal story: About 42% of American adults currently have obesity, according to the CDC. This is part of a troubling long term trend, as rates of obesity have more than tripled since 1960.
And this problem is certainly not confined to the US. Globally, overweight and obesity prevalence is projected to reach 51% by 2035, and obesity has emerged as the second most significant modifiable risk factor for mortality worldwide (after smoking).
From Fryar et al, 2020
As researchers work to understand the factors influencing food intake and weight regulation, environmental conditions, like temperature, have emerged as intriguing variables.
Cold exposure, in particular, presents a complex puzzle. Animal studies suggest that cold exposure can boost energy expenditure by activating the sympathetic nervous system and brown fat tissue, potentially promoting fat burning via cold thermogenesis. However, at the same time, feeling cold also appears to stimulate appetite — perhaps as an evolutionary adaptation to prevent starvation during harsh winter conditions.
In the modern food environment, where we can eat whenever and whatever we want, you can imagine that this cold-induced appetite stimulation could become problematic.
This raises some key questions: Does cold exposure significantly increase fat burning in humans? And if so, does it increase energy expenditure enough to offset the accompanying rise in appetite that many of us tend to experience?
A new intervention study provides valuable insights into these questions.
Inside the Study
To understand how being in a chilly environment affects eating habits, NIH researchers recruited 47 volunteers.
Each participant spent four 24-hour periods in a metabolic chamber — basically a hotel room-sized laboratory that can precisely measure energy expenditure.
In two of these stays, the room was kept at a comfortable 74.3°F. During one session, participants ate prescribed meals in specific amounts. At their other session, they could eat whatever they wanted, whenever they wanted, from an available selection of foods.
The other two stays were identical in setup, except that the metabolic chamber was cooled to 66.2°F. Not super cold — pretty close what you might experience in a chilly office building.
Again, one visit had controlled meals, while the other allowed free eating.
By comparing what happened during these four different scenarios, researchers could see how cold affects metabolism when food intake is controlled, and how it influences natural eating behavior when people are able to eat freely.
What They Found
Sure enough, when participants were confined to the cool room, they ate significantly more, compared to when they were residing at a comfortable temperature.
On average, people consumed an extra 411 calories during their 24-hour cold exposure — about the equivalent of a medium serving of fries. This represented a 13% increase in their daily food intake.
Blood work revealed, at the biochemical level, why the subjects were driven to eat more. When they were in the cold room, levels of ghrelin, often referred to as the "hunger hormone," went up. At the same time, levels of leptin, a hormone that reduces appetite, declined.
Curiously, despite the cool temperature, participants didn't burn significantly more calories in the 66.2°F room, compared to when it was set to 74.3°F.
Here's the good news: this increased appetite didn't seem to persist into the next day — once they were back at a normal temperature, participants returned to their usual eating patterns.
Real World Applicability
So, when participants spent 24 hours in a cool room, they ate significantly more food — without burning more energy to make up for it.
Does this mean that they would ultimately gain weight if they were to stay immersed in a cool environment?
Well, it's actually sort of hard to say.
Physiology is complicated, and bodies do have an array of compensatory mechanisms that can kick in over longer timespans. You can imagine that longer-term cold exposure might elicit adaptations that would balance out the greater energy intake. For instance, people who live in cool homes may wind up developing more brown fat tissue, which would burn more calories to generate heat.
But there is some epidemiological evidence indicating that living in a colder indoor environment is indeed linked to weight gain.
A population study examining data from more than 100,000 people in England found that participants living in warmer indoor temperatures (above 73.4°F or 23°C) had significantly lower BMIs, compared to those who resided in cooler homes (below 66.2°F or 19°C).
(Note that those temperature thresholds are almost exactly the same as the conditions that participants experienced in the metabolic chamber in our featured intervention study.)
That certainly suggests that remaining in a cool ambient environment, long term, could result in maintaining a higher body weight.
What This Means For You
Fortunately, most of us have some degree of control over the temperature of our homes. If you are struggling with your weight, adjusting your thermostat could be a relatively painless way to modulate your appetite (might also save you some money in the summertime, as an added bonus).
A more formidable challenge might be our workplaces — a typical office building is often maintained around 68°F, meaning that many of us spend substantial portions of our day immersed in chilly environments.
Indeed, an earlier study examining office workers found that participants consumed 357 more calories on average when they spent a 7-hour workday in a cooler room (66-68°F). Sounds like a real-world version of the lab study we just discussed, doesn’t it?
Even if you’re not in charge of the thermostat, there are things you can do if you have to spend a significant chunk of your day in a cool room. Obviously, you can try to improve your thermal comfort via space heaters, heated blankets, hot beverages, etc. But another strategy to get around this is to structure your eating into defined meals, rather than grazing or eating whenever hunger strikes.
One way is simply not to eat at all — set up a schedule of time-restricted feeding, and just don’t eat during the window of time that you’re at work or school or wherever.
The other option — perhaps more realistic — is to rely upon pre-portioned meals and snacks. This allows you to make food decisions ahead of time, rather than in the moment when your appetite might be artificially elevated by the cool environment.
Random Trivia & Weird News
🎄 This week, Belgium's food safety agency warned residents not to eat their Christmas trees.
They say every disclaimer tells a story — and it’s usually a weird one.
As the holidays are winding down, the Belgian city of Ghent, noted for its environmental initiatives, recently suggested residents could responsibly dispose of their Christmas trees…by eating them.
To that end, the city's website offered tips for transforming pine needles into culinary creations, suggesting they could be used to make flavored butter.
The recommendation immediately prompted Belgium's federal food safety agency (AFSCA) to issue an unlikely dietary warning:
"Christmas trees are not destined to enter the food chain."
The agency went on to explain that most Christmas trees are treated with pesticides and sometimes flame retardants, making them potentially dangerous to consume. "There is no easy way for consumers to tell if Christmas trees have been treated," they warned, noting that such uncertainty "could have serious, even fatal consequences."
Photo credit: oxygen/Getty Images
Podcasts We Loved This Week
- Tommy Wood & Josh Turknett: Does napping accelerate learning? Via Better Brain Fitness.
- Oliver Burkeman: The productivity paradox — why less is more. Via Plain English with Derek Thompson.
Products We Like
SOMOS Mexican Black Beans
These are tasty and efficient — ready in just 90 seconds. You can use them to make tacos, add them to soups, or just eat them as they are. They're particularly good for meal prep since they’re much drier than canned black beans, and they maintain their texture even after reheating.
Along with their versatility, they are super healthy: each packet contains 15 grams of fiber, 20 grams of protein, and 1390 mg of potassium.
You can find them at a lot of grocery stores, or you can order them via Amazon, currently just $19.68 for a pack of six.
humanOS Catalog Feature of the Week
Food Environment and Weight Control
This week, we’d like to highlight one of the courses from the Ideal Weight Program, developed by our good friend Stephan Guyenet.
Today’s study highlights how environmental factors can powerfully influence our food choices — often without us even realizing it.
In this course, Stephan demonstrates how lots of seemingly small changes in our surroundings can have a surprisingly large impact on what and how much we eat. He also digs into some practical, evidence-based strategies for restructuring your environment to support healthy eating habits with minimal reliance on willpower.
Wishing you the best,
