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Notes -
What's the best body temperature?
Bryan Johnson, anti-aging zealot, recently raised eyebrows on X when he claimed to have a body temperature of just 93.4 °F (34.1 °C). He claimed that this was evidence of superior health. To me, his claim seems immediately suspicious and more likely to be a faulty measurement. Others pointed out that it would be very difficult for his body to fight infection at such low temperatures.
Nevertheless, body temperatures do vary between people and, interesting, over time.
We all "know" that the normal temperature is 98.6° F (37 °C). As it turns out, this was true once, but no longer. Body temperatures have been consistently falling. Today, the average temperature is closer to 97.9. My temperature is typically around 97.
Why is this happening? No one knows. Of course, many people blame measurement error. Other theories are that 1) people today have lower infection load 2) people today have lower metabolisms. #2 does seem likely. When we look at historical records, we often see even relatively sedentary men ate 3000, 5000, or even more kCals per day. Now, many men (myself included) will maintain their weight at 2000–2500 kCals, even with exercise.
The good news? There does seem to be some indication that lower temperatures correlate with longer life spans (in mice, of course). This is likely to be similar to caloric restriction where it might help humans, although not nearly as much as mice.
But what if I don't want to live forever, I just want to look good naked and have tons of energy? It turns out that there are people who take the opposite approach as Bryan Johnson and say that we need to increase our body temperature. For one, it will help prevent illness. But it will also increase one's metabolism, giving a person boundless energy, and allowing him to eat like a hummingbird while looking lean and ripped. Here's a guy who invented a diet where you can eat unlimited sugar before 3pm. There was another guy on Twitter who posted about his sugar maxxing diet and bragged about his body temp of 99.5. He looked pretty ripped. (Curse you, Twitter search).
These high-temperature guys all seem to follow an obscure Oregon dietician named Ray Peat who doesn't have a Wikipedia article, and is indeed only mentioned in Wikipedia on the article for Bronze Age Pervert. From the best I can tell, Ray Peat ate something like 3500 calories a day, half coming from simple sugars. He died in 2022 at age 86.
So, what's your body temp? What should it be?
Huh? Where are the historic sedentary men eating over 5000 calories on a daily basis?
It's going to be hard for me to dig that up. It was on X and was based on records of courtiers in some European country.
Not the same, but here's the best I could do with 3 minutes of Perplexity: Trench soldiers eating 4600 kCals per day during WWI. Obviously, they were very active, but also must have weighed an average of like 140 pounds.
https://medicalmuseum.health.mil/micrograph/index.cfm/posts/2023/beef_bread_and_coffee_food_innovations_during_world_war_I
Even assuming extreme activity, this should only burn less than 3200 kCals per day: https://tdeecalculator.net/result.php?s=imperial&g=male&age=19&lbs=140&in=69&act=1.9&f=1
I've seen many other records of historical people eating large amounts of calories. Maybe they're dubious, I'm not sure.
These guys were probably fat. I can definitely buy a sedentary fat man eating five thousand calories a day.
It's pretty believable that trench warfare has higher caloric demands than athletic training. Athletes stop training once they are in danger of overexerting themselves, while the infantry has no such luxury.
That trench soldiers maintained weight on 4600 calories a day should make us extremely skeptical of sedentary, normal BMI people eating 5kcal day in, day out unless they have some kind of metabolic disease, let alone this happening often.
This is begging the question.
You assume that caloric consumption is determined almost entirely by activity level, and therefore any evidence against this theory must be wrong somehow.
My post of course, was about body temperature, not really about the causes of obesity, but I do understand the temptation to latch onto the hottest and most bikeshedd-y of all culture war items: the CICO thesis.
In any case, since I can't resist either, I will propose that higher body temperature provides a possible mechanism for people to burn a much higher (or lower) amount of calories than can be explained by the Mifflin-St. Jeor Equation.
What evidence?
I didn't see anything especially notable in the post except for this wild claim I'd never heard of before of skinny people often putting away over five thousand calories a day in the past.
There's obviously some degree of RMR difference between people (and the existence of people at the tails of the RMR distribution does not contradict CICO in the slightest btw).
However, it's notable that people are eating way more food these days than at basically any point in the past. That figure is a little rough since it doesn't actually measure what people are eating - those numbers show a similar story but they only seem to go back to the seventies. So it's a little hard to imagine that our ancestors had significantly higher metabolisms while eating significantly less. Small changes are possible and not that interesting to me.
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