I strongly disagree with this interpretation of those overfeeding studies. From what I can tell (though I couldn’t access every study SMTM cites), “overfeeding” is usually defined relative to the output of one of the typical BMR/TDEE estimation formulas given a person’s parameters, not based on actual measurement of a subject’s TDEE. Those formulas are fine for a baseline guess, but even the most accurate ones are going to be substantially off in either direction for a fair number of people! Some of the difference is unaccounted-for NEAT, some of it is differences in absorption efficiency, some of it is probably other factors we don’t understand yet. Given the known reality of interpersonal variation in what your actual calories in and out are relative to their naive estimates, some subjects not gaining weight while “overfeeding” is exactly what you’d expect to see.
A fun fact: my estimated “effective TDEE” is (averaged over months) pretty consistently around 3300 cal/day for the past 18 months—rarely more than +/- 100 cal/day off in either direction—whereas the best formula I could find (using my body fat %, as actually-measured by a DEXA scan) says it should be something more like 2600-2800 cal/day. This is based on weighing my body daily and recording the caloric intake from actually-everything I eat, almost always weighing food when necessary rather than coming up with estimates.
I strongly disagree with this interpretation of those overfeeding studies. From what I can tell (though I couldn’t access every study SMTM cites), “overfeeding” is usually defined relative to the output of one of the typical BMR/TDEE estimation formulas given a person’s parameters, not based on actual measurement of a subject’s TDEE. Those formulas are fine for a baseline guess, but even the most accurate ones are going to be substantially off in either direction for a fair number of people! Some of the difference is unaccounted-for NEAT, some of it is differences in absorption efficiency, some of it is probably other factors we don’t understand yet. Given the known reality of interpersonal variation in what your actual calories in and out are relative to their naive estimates, some subjects not gaining weight while “overfeeding” is exactly what you’d expect to see.
A fun fact: my estimated “effective TDEE” is (averaged over months) pretty consistently around 3300 cal/day for the past 18 months—rarely more than +/- 100 cal/day off in either direction—whereas the best formula I could find (using my body fat %, as actually-measured by a DEXA scan) says it should be something more like 2600-2800 cal/day. This is based on weighing my body daily and recording the caloric intake from actually-everything I eat, almost always weighing food when necessary rather than coming up with estimates.