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Hungry, hungry humans balance the energy budget by … cutting inflammation?!

 •  • by Paul Ingraham
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Maybe we can convince our body to spend a bit less energy on defence: reduced immune system activity, AKA inflammation, that holy grail of general health. Optimistic, science-based life hacks are not my usual style, but I think this one’s cromulent (wouldn’t publish it if I didn’t). It takes some proper splainin’, but the journey is interesting, and the destination useful: a new scientific justification for exercise as medicine for chronic pain.

First you need to know that humans are unusually fuel-hungry critters. We burn through calories much faster than any other primate. The old idea was that homo sapiens uses energy like other animals, but that reasonable assumption was knocked over surprisingly recently, by evolutionary anthropologist Herman Pontzer.1

In fact, humans need quite a lot of fuel, probably because of all the brains. Brains are expensive.

Pontzer et al. used the most new-fangled methods to measure energy usage in people of all ages — 8 days to 95 years. Highlights:

  • Toddlers are the metabolic champs, hitting 50% more energy burning than their parents.
  • The power hunger declines to adult levels by about the age of 20.
  • After 20, metabolic demand remains relatively stable for a long time, declining quite slowly over forty years, even during pregnancy.
  • In the seventh decade, larger declines in calorie-burning start to kick in.

That’s all “fun facts,” but another result might be a little more consequential.

Animated GIF of a realistic looking brain wobbling.

All brains are metabolically “expensive,” but this one burns extra calories from all the wiggling.

Homo sapiens is also amazingly good at balancing the energy budget

Human also keep our high total cost of activity surprisingly consistent over time. If we exercise more, our clever biology starts to actually cut back on other metabolic expenses — so we don’t burn as much extra fuel as we expect.

This does not mean that the exercise is futile! Despite some hype to contrary (doubling down on the idea that “you cannot outrun your diet”), exercise is still a valuable part of any weight loss plan, for instance.

But every calorie counter knows all too well how much harder it is to get rid calories than it is to shovel them into our pie holes in the first place … and this new data means the deck is even more stacked against us than we thought.

So: the body tends to actually reduce overall metabolic spending, the better to afford extra exercise. That budgeting adjustment is cool, and not especially controversial as far as I know. (Although saying that is like casting a magic spell that summons an expert to put me in my place: “experto correctium!”) Now for the cool part…

Where exactly these metabolic spending cuts happen?

What gets sacrificed? This is where this all plugs into the world of pain science. Pontzer postulates (as quoted by Gibbons):

“I think we’re going to find these adjustments lower inflammation, lower our stress reaction. We do it to make the energy books balance.”

That is quite a thought. Is Pontzer nuts? No, it’s just legitimate speculation. If true, it would be a tidy new way to explain why exercise is such good medicine.

The need to conserve fuel for exercise may reduce how “seriously” the body takes its stress — how much energy we invest in maintaining better-safe-than-sorry levels of immune system function.

Fresh evidence that exercise does indeed tame inflammation

While this post sat in my drafts folder for a while, Pontzer’s team published the results of a test of this hypothesis.2 Bravo! Nice timing!

They crunched the numbers in a big health database to find a long-term relationship between energy expenditure and inflammation, and found it: sustained daily physical activity was linked to reductions in the several major biomarkers for systemic inflammation, like C-reactive protein (CRP) and white blood cells.

So this intriguing idea is now at least partially evidence-based, and relevant to chronic pain — which is often more about biology than biomechanical strain and tissue failure.

Notes

  1. Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021 08;373(6556):808–812. PubMed #34385400 ❐ PainSci #51994 ❐
  2. Klasson CL, Sadhir S, Pontzer H. Daily physical activity is negatively associated with thyroid hormone levels, inflammation, and immune system markers among men and women in the NHANES dataset. PLoS One. 2022;17(7):e0270221. PubMed #35793317 ❐ PainSci #51450 ❐