And even more specific: “How hot does this bath have to be?”

But what stuck with me were these: “Any suggestions as to what I should be paying attention to? … Every damn thing I read says something different.” And “Dummy here. Say more! I’d read.”

So I will say more, though I’ve already said a lot about why calorie-counting is an ineffective approach to eating. Calories are a crude metric that takes into account nothing about the properties of foods other than the total energy they contain. The value of activities can’t be reduced to a number, and nor can foods. Still calories are listed everywhere, enumerated in enormous fonts on food packaging and across menus and ads for packaged products with nothing to recommend them but a lack of calories.

A calorie is the amount of energy required to raise the temperature of a gram of water by one degree Celsius. The “calories” we talk about in food are the amount of energy released when that food is burned. Of course the first law of thermodynamics applies to humans, so if you take in less energy than you use, it’s impossible to store that energy (as body fat). But the factors that go into energy balance are many. The body burns and stores energy from different foods in different forms at different times in different people in different ways.

That crudity leads to mistakes, like the idea that 200 calories of Skittles are in any way equivalent to 200 calories of salad. In that way, calories have been weaponized by marketers to claim their ingestible products are innocuous. As Coca-Cola has advertised, for one, drinking soda is fine as long as you exercise enough to burn off those calories. That’s reasonable if it weren’t also true that constant exposure to high-sugar foods changes the way our bodies store energy. It’s like saying it’s fine to insult someone as long as you follow it with a compliment.

Worse still are the loudly advertised “100-calorie” packs of sugar-based edible products. They cause insulin levels to surge, affecting nutrient absorption and subsequent hunger in ways fundamentally different from eating 100 calories of almonds or spinach. That’s so much spinach. It would fill your stomach and please the microbes of your bowel.

I could go on, but suffice to say that evaluating food by its calorie count is like evaluating literature by the number of pages in a book. It’s usually worth knowing whether you’re committing yourself to something like The Stranger or something more like Infinite Jest, but the number alone is a poor measure of what that book will do for your health. A day is not measured in number of pages read, nor a person by the number of books on their shelf.

Of course, calories are indeed a valuable tool for researchers parsing the intricacies of human physiology. The bath study was a novel investigation of the immune system. It appears in the March issue of the journal Temperature, under the title, “The effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?” (Not the clickiest headline.)