Cold, Muscle, and Blood Sugar: How to Use the Metabolic Effect, and When Not To
The 43 percent finding was really about muscle, not brown fat, and that changes everything about how you should time cold around food.
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Of all the metabolic claims made about cold, the effect on blood sugar is the one I find most genuinely interesting, and the one most often explained wrongly. In the free companion piece I laid out the two studies that matter: a 43 percent jump in insulin sensitivity in one, and nothing in another that prevented shivering. This piece is about what that contrast actually means, and how to use it, and when not to.
A note on who is writing this
I am Dr. Susanna Søberg. I am a metabolic scientist with a PhD from the University of Copenhagen, and I have spent more than fifteen years researching metabolism and the body’s response to stress, cold, and heat. I published the Søberg Principle in Cell Reports Medicine in 2021, and I wrote a book, Winter Swimming, now translated into fourteen languages. This began for me as science. Over the years it also became personal.
My mission is simple, and it is the reason this journal exists. I want to give you the truth about cold and heat, both halves of it at once: what the science genuinely supports, and what is oversold. Safety and benefit matter to me equally, because advice that ignores either one is not worth giving. A benefit you cannot reach safely is not a benefit, and caution without benefit is just fear.
There is a great deal of noise online about this subject. I am not going to spend my time reacting to all of it. What I can do, here, is give you my advice grounded in the actual research: the studies that have been done, read honestly, alongside an equally honest account of where the science does not yet exist. Where we lack the evidence, I will say so plainly.
In this piece:
Why the insulin sensitivity effect is a muscle story, not the brown fat story you were sold
What the shivering result tells you about how to actually practise
How to reason about cold timing around meals, from the physiology up
Fasted versus fed cold, and which suits which goal
Raynaud’s: how to approach cold with it, not simply avoid it
The honest limits, and who should not do this without medical guidance
