Dr. Cheung: The Impact of Cold on Metabolism and Fueling

In his new Workshop The Impact of Cold on Metabolism and Fueling released just a few days ago, Dr. Cheung shows that the ambient temperature of your training environment has an impact on the fuel mix our bodies burn during exercise.

@ThermalDoc, your Workshop inspired a few questions that I wonder if you would have some time to answer.

  1. How were the test subjects dressed in the neutral and cold temp training environments?
  2. How much skin exposure in cold temps do you think is required to trigger this change in the body’s fuel preference?

I ask because my winter “endurance sport” is winter camping with a Boulder-area Scout troop. Every winter, we are seeking “frost points” (1 point for every degree below freezing per day spent camping). Daytime average temps are usually 20-30 degrees Fahrenheit/-6 to -1 Celsius. Early evening and nighttime temps often drop below -12 Celsius.

Winter camping does not require the same exertion as an endurance sports workout, but neither is the effort level easy. Just walking around in the snow in heavy boots, carrying gear, etc. is definitely higher METs than normal walking. We sustain that effort level for hours at a time with some breaks. We are wearing 3-5 layers so skin exposure is mostly face and sometimes hands.

During these winter campouts, I’ve noticed that both adults and Scouts tend to favor high-fat, hearty foods. Your Workshop makes me wonder if this is more than just a flavor or cultural preference! Perhaps our bodies crave higher fat fuels in cold weather because of this fuel mix response.

Thanks for any insight!



Hi @dave . In those studies the participants wore the same clothing in both neutral and cold conditions. They were dressed for neutral, so they were underdressed for the cold, hence the lower skin temperatures.

In terms of how much skin exposure is required to trigger the change, we’re not sure but my feeling is that it’d be more than just having your face and hands exposed as may be typical with winter camping. The main trigger seems to be a decrease in skin temperature that is cool but not to the point where you’re actually dropping core temperature. So maybe wearing one layer less than you might while doing winter activities. As you know, the key with physical activity in the cold is to be exercising at a pace where you’re not dripping sweat or really feeling like you’re sweating a lot, as the sweat on the skin and the clothing is going to quickly cool you down.

It may indeed be that the preference for high-fat foods in cold conditions is an evolutionary adaptation to ingest more calories. Certainly for cold weather ultras like the Iditabike and mountaineering expeditions, it’s all about maximizing calorie intake, and fat is much more calorie dense.

Stephen Cheung

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I live in Northern MN and do the winter ultras. I realize I’m only a study of one, but my experience matches your results. When temps drop below 0F, I really crave fats and other savory food. The typical sports nutrition carb stuff isn’t what I want. However, my caloric need vs summer is dramatically higher. I weigh 145. Rough estimate— in summer I eat about 250-300 cals/hour. In winter it’s closer to 400-500 (or more at times). Eating that much is a challenge (especially when anything you bring has to be edible when frozen) and I’ve found I need a mix of foods—from fatty things like nuts & nut butters to Honey Stinger waffles. The latter may not be what I’m craving, but it’s what will digest better at that given moment.

As for water, I have read for years, and really have no reason to disagree with the notion that it’s really easy to become dehydrated in the cold dry air. However, with a major goal being to stay dry if I’m out for more than 2-3 hours, I really don’t sweat much. I probably only drink 12ish ounces of water/hour during winter rides at LT1 or below (as opposed to 18-20 in summer).

Anyways that has been my experience. I really appreciated your video. There is so little scientific testing done on cycling in truly cold conditions.


Patrick, I wonder if body composition is a factor. I weigh 134 lbs and most of our Boulder, Colorado adults and kids are pretty lean. We definitely crave those heavier foods, though Dr. Cheung points out that we might not expect this change in fuel preference with so little skin exposed.

I will admit that just thinking of eating sugary foods or endurance sports products like gels during winter campouts will often make my stomach turn. This may be personal or perhaps related to being at altitude (we’re usually around 9-10K feet) since altitude has thirst and appetite suppressing effects on top of the dehydrating effects. I’m in agreement with you that cold, dry air just sucks the water out of you, too.

Both thirst/appetite effects are pronounced enough with our kids that, about once a year, a kid will eat one of these heavy meals he is craving during a winter campout and then barf up the whole thing because he is too dehydrated for the meal to clear his stomach.

Dr. Cheung, thank you for the thought-provoking Workshop and your response!


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