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PaperclipPerfector  4mo ago (text post)   2561 thread views

Small-Scale Question Sunday for November 24, 2024

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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?

When we look at historical records, we often see even relatively sedentary men ate 3000, 5000, or even more kCals per day.

Huh? Where are the historic sedentary men eating over 5000 calories on a daily basis?

Monasteries in the late Middle Ages, mostly.

These were well known for obesity.

Where are the historic sedentary-by-modern-standards men full stop?

Based on my own calorie requirement, a "sedentary" lifestyle without a car requires at least an extra 500 calories per day compared to a US-suburban sedentary lifestyle.

fireinabottle.net has some really interesting posts about historical calorie consumption. One I remember was about consumption in New York. I don't know if it ever got to 5000 calories, but it was certainly a high number. And he's also written about body temperatures declining over time. He attributes it to increased PUFA consumption from vegetable oil.

Annoyingly, the site seems to be down now, so I can't point to any actual posts.

One I remember was about consumption in New York

I don't have a link handy, but I seem to recall it being demonstrated to my satisfaction that what the Fire in a Bottle guy and the Slime Mold Time Mold guy were presenting as evidence of high historical calorie consumption failed to account for food wasted rather than eaten. Like annual production divided by number of people or something.

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.

records of courtiers in some European country.

These guys were probably fat. I can definitely buy a sedentary fat man eating five thousand calories a day.

Trench soldiers

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.

From first principles, active bodily processes to either heat or cool one's flesh likely consume calories. Temperature gradients need to be maintained. In fact, I've seen work posing the question of the effect of indoor environment control on caloric expenditure (if you have electricity doing the work of regulating your environment, you likely have to expend less). Given that most people maintain a body temperature above that of ambient, it is theoretically plausible (even likely) that increased body temperature would increase caloric expenditure.

Of course, the rub usually comes in terms of magnitudes. How big is the effect? A casual scan of the literature doesn't turn up anything all that great. So, I would maintain my personal belief that there is likely a positive effect, but extremely low confidence in any sense of an estimate for magnitude.

Concerning equations, the question always is what it is that you're trying to do. For very small groups, you can go through a very intensive process of measuring all sorts of body characteristics, down to the size of individual organs, and use some pretty detailed estimates to try to get really close. Most people don't do anything like that; it's just too much effort. Instead, people often want to collapse larger-group data into a handful of variables for ease of estimation, knowing that any such effort will inherently have variability and error bars. The equation that you get, and how much variability it has, depends on which type of population you're targeting and which variables you're trying to collapse it down to. Obviously, targeting larger/smaller population types tends to increase/decrease variability; similarly, increasing/decreasing the number of variables (under mild assumptions of them being correlated at all to the dependent variable and not entirely codependent) tends to decrease/increase variability. If you're considering fit and athletically-active populations, a lot of folks recommend the Cunningham equation. It also does not include typical body temperature. I'm not sure what the codependence will look like, what the rough magnitude of the effect will be, and how much additional variability you could cut out by including typical body temperature, just because I'm not aware of anyone who has taken the time and money to specifically explore it.

therefore any evidence against this theory must be wrong somehow.

What evidence?

I do understand the temptation to latch onto the hottest and most bikeshedd-y of all culture war items: the CICO thesis.

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.

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.

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.

All but one were eaten by Henry VIII.

Interesting.

My husband tended to be 99 F when he was younger, and also attracted way more static electricity than I do. He eats things like an entire pound of bacon, then just paces a lot, or walks around barefoot in the snow or something. My daughter seems to have inherited his metabolism, and actually was sent home from pre-K a couple of times for "low grade fever," but then she got home and didn't have a fever.

My body temperature is a bit below average (I don't check it very often, because I almost never run a fever), and I'm lower energy, but also have fewer random health problems -- things like almost never getting headaches or nausea, even when we eat something a bit off, getting over colds and flus faster, stuff like that. This has been good for pregnancy, which went smoothly all three times.

There seem to be trade offs involved.

There seem to be trade offs involved.

There is a "woo" explanation that goes something like this:

In all plants and animals, there is a thrive/survive dynamic. During times of plenty, the plant will blossom, the animal will expend energy and look to breed. During times of starvation, the plant will go dormant, the animal will hibernate.

But the candle that burns brighter (high metabolism) is extinguished sooner. High metabolism may lead to better health, more energy, and visible abs, but it will also age one more quickly.

This is a universal principle of all life forms.

This woo stuff is maybe directionally accurate. It's certainly not very well-studied. Maybe I'm just hoping there's an upside to my vampire like pulse rate and body temperature.

When I was younger, my normal body temperature was around 99.7. I ate a terrifying amount of food, yet even without any regular exercise other than walking, I had a BMI that was barely above underweight. I thrived in cold weather, my blood pressure was on the verge of being too low, and my resting heart rate was in the 50s. I’m also fairly tall, and, interestingly, also used to generate a lot more static electricity than most other people I knew (@Gaashk, are you aware of any connection between body temperature/metabolism and static electricity?).

Unfortunately for me, it seems there may be something to your theory. Not only do mice studies present me with a bleak picture of my future, but when I compare myself to my former classmates, I seem to be wrinkling much more rapidly than any of them, even though I generally have a vampiric aversion to the sun, while they spend much more time in it.

Perhaps I should just take this as a hint from the universe to stop procrastinating and do something more with my life before my time is up.

Please let me know if you find out something useful about this topic.

FWIW, I also eat like a combine harvester, pace a lot, don't gain weight, and my skin ages poorly.

Not sure if there is anything to it all; maybe we're just reading too much into a bunch of coincidences.

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