New Study: The Lifestyles and Metabolism of Underweight People

Saw this on Twitter today…

Higher than predicted resting energy expenditure and lower physical activity in healthy underweight Chinese adults

Twitter Commentary:

UCSF Cardiologist Weights in:



“Third, surprise was they had much higher metabolic rates than predicted from their body composition and that was associated with elevated levels of circulating thyroid hormones, particularly T3, T4 and fT4”

I wonder how much higher? On keto, I’ve significantly reduced my fT3, my body revs much lower, a “pseudo-starvation” feedback signal from the hypothalamus.

And the 12% less food intake…that would be a huge signal over time towards lower BMI.

The few people I know who I would associate with this phenotype…they do not snack or eat constantly. They may not eat classic healthy diet “eat whatever they want”, but don’t eat the totality of calories of a heavier BMI person from small population observation.


I found this particularly interesting…

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Yes and no…being lean is a low nutritional energy trafficking phenotype, ergo, low TG, LDL by default. Now, whether this translated to say lower cardiometabolic (eg. VO2max, CAC) is another matter. He admits possible confounders re diet.

That’s a fact. During the covid lockdown, I couldn’t go to the gym, but I kept my weight down, practiced TRF, etc., and my blood markers were great, not just the lipids. Started rapamycin, went back to the gym and my markers aren’t as good.
What does this mean? I really don’t know.

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Very cool stuff!

I always like it when we challenge our norms of standard blood tests being the final word on how healthy you are vs. unhealthy. Just because you can move a number to a “better” range does not mean have improved your health.

The thyroid component is extremely interesting since there are some in hormone world that feel “optimizing” your levels based on how you feel. The psychiatric community has been using some T3 (cytomel) for resistant depression - I believe this in Europe, but I have had a psychiatrist send me a few patients to treat with thyroid medication even though they had normal TSH :slight_smile:

When I went keto, one meal a day, it threw my thyroid markers for a loop. I had the literature and everything is exactly as it should be. Brain thought I was in “pseudo-starvation” mode, significantly lowered fT3. Bio hack.

So my doc, thinking something was “wrong”, even though I told him “I feel amazing”, decided he would medicate me to adjust. He threw the KITCHEN SINK at it, ZERO response. I finally laid down the 1" high stack of literature on his deck (he has no keto patients), and he relented.

Anyway, I built some “capital” with my doc that has come in handy…he became far more supportive of my outside the box longevity interventions, eg. rapamycin.

The very first thing he asks me in every consult “how do I feel”…to your point.


I am this person. BF 10% BMI is 18.
I eat way less than others. I have never had the appetite to eat normal portions. At various times I’ve tried to eat more to bulk up but I just cannot stand to overeat.


What height and weight give you a BMI of 18?

5’ 8" 123 lbs
not very heavy

Understatement of the day. Have you always been this BMI throughout life? Anyone else direct lineage similar phenotype?

brothers are all heavy
I’ve been as heavy as 145 when I did the 3 donuts a day thing in my 40’s

So if you were as high as 145, and now 123 and you seem to suggest “a reduced donut intervention”…are you consciously trying to loose and remain at low weight? You didn’t intervene on the way down by design, or it just happened naturally?

retired from stressful job with access to donuts and went RVing full time. So I spend my days mountain biking or hiking rather than behind a desk eating donuts. More calories and healthier diet not deliberate but side effects of new life.
Also, lost about 5 lbs with use of rapamycin.


What WERE their stress hormones/glucocorticoids like? GCs can increase metabolism/thyroid activity and increase catabolism/decrease inflammation while increasing aging rate. Also CR mildly increases GCs (tho there’s a HUGE difference between mildly and drastically increased stress hormones)

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