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Fat or Muscle: Which Keeps You Warmer?

JD Hancock on Flickr

The other day I was chatting with a friend who, despite the heat outdoors, had a coat on indoors because of air conditioning. I happen to be slightly overweight, so I teased her she should emulate me to keep warm. Did I mention this person is into yoga, healthy eating, basically everything I should do but don’t?

The discussion led to an interesting question: which is better for retaining body heat, fat from too much ice cream and Oreo cookies or lean muscle from yoga and clean living?

These Off Beat articles are about technology, science, and sometimes computer science, but they're mostly unscripted adventures in online research. They also teach how to define and answer real world questions with online research. They're also the last or next to last article I write for each issue of the magazine and, therefore, a way to blow off steam and relax.

Plus these Off Beat articles are meant to be fun: there will be detours.

The question I want to answer this month: which keeps you warmer, a pristine body mass index number or a nice layer of chubby on your body?

It turns out there is quite a lot online about this topic. We weren’t the only two people on the planet debating the merits of muscle versus fat.

(Of course, the value of clean living versus reckless abandon is a totally different debate, one subject more to belief than measurable facts like the heat retention properties of muscle versus body fat. A gourmand and an ascetic could argue opposite views and both be correct.)

But I digress.

Whales, Seals, and Other Chubby Mammals

I began by typing the search phrase which keeps you warmer, fat or muscle? into the Duck Duck Go search engine. The first few results were articles about sea mammals that every person knows have lots of blubber. If we were seals, indoors in air conditioning, presumably we would be nice and toasty warm.

That’s the argument I found on ChaCha.com (great site name, BTW). Buried in a sea of advertising is the simple statement, no counter argument necessary, “Whales are covered in fat (blubber), keeping them warm in the Artic.”

However, BodyBuilding.com had a forum post that disagreed. Someone there argued “Fat, keeps you warm, because what makes you cold is the temperature of your blood dropping. Muscle doesn’t cover your veins, which means your bloods temperature is still being affected the external temperature.”

Near the bottom of the BodyBuilding.com thread, a kinesologist felt compelled to call all the earlier answers moronic, added he went to a school with great looking women (you think the person is in their teens, maybe?), and then proceeded to explain muscle is mostly an organ whose function is to burn fuel and keep you warm. So you don’t need body fat! He then explains human body fat does not retain heat well, not as well as whales and baby seals.

The Real Story (with Science)

The Duck Duck Go search results also led to another site with a great name, Go Ask Alice, from Columbia University in the US. The question they answer: does eating fat in the winter help keep you warmer?

The answer is yes and no. Consuming any food burns calories which generate body heat. After a truly wonderful description of how metabolism and calories work, there is this bit of explanation:

When we “burn” calories, our bodies experience a slight elevation in temperature, and Chilly, here’s the lowdown: when we are feeling cold (in NY or anywhere), our metabolism slows down a bit. That’s why we shiver: our body is attempting to create heat and keep our internal organs warm. When we feel hot, such as when working out, our bodies expend more energy to cool off.

A link in this Go Ask Alice article answers another burning question, does fat turn to muscle and increase body weight? Apparently fat and muscle are two distinct types of tissues and, therefore, cannot convert one to another. Who knew? Apparently athletes who develop massive muscles for their sport get fat after they retire because they consume too many calories, increasing body fat, not because their muscle turned to fat.

But let’s get back to the real question: is your body temperature warmer when you’re skinny and muscular than when you’re chubby?

I switched to the Google search engine because, beyond Go Ask Alice, many of the sites appeared to have questionable legitimacy. Plus, while debating this question with my friend the other day, I had Googled the question and discovered lots of interesting results. However, I did wait until writing this essay today before actually reading the results. Honest.

Wiki Answers, for example, says fat is a better insulator but muscle is what generates body heat. You need both. And New Scientist tells a sad story, if you love mice, about a test which revealed the absence of brown fat in the body does not prevent you from staying warm in chilly temperatures: your muscles generate heat. Before this research, it was believed brown fat in the human body was solely responsible for heat generation.

Specifically, the research reported in New Scientist indicates a protein called sarcolipin triggers heat generation in muscles. The lack of sarcolipin also can be an indicator of obesity, what happens when you do not burn all the calories you eat.

And you’ll be proud of me to know I managed to NOT click on two other New Scientist articles, Ancient water cache may be pristine primordial soup and Deepest-diving sub implodes in Kermadec trench. I saved them to Pocket to read later. And linked them below in case, like me, you enjoy being easily distracted.

Instead, I continued to look through other answers to this question, which keeps you warmer, fat or muscle? Or as the Diving Blog puts the question, Do Fat People Stay Warmer? Ouch, so insensitive. The site argues it is the combination of lean muscle and fat insulation in the human body that determines if you can stay warm in a cold room. Despite the insensitive title to his article, the person does have the kindness to suggest his answer to this question is not an excuse to eat more cheesecake.

The Skinny

It appears the answer to the discussion with my friend about what keeps you warmer, body fat or muscle, turns out to be both. You want some fat as insulation. But you also want to exercise to develop enough muscle to generate body heat. All things in moderation, in other words.

Perhaps I’ll wait a day on the bagel with cream cheese and choose, instead, to walk for half an hour today.

Learn More

Which keeps you warmer, fat or muscle?


Ancient water cache may be pristine primordial soup


Deepest-diving sub implodes in Kermadec trench


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