I think you are missing my point—which EY also makes above—that you are concluding that the calorie consumption increase causes obesity when in fact none of the evidence you provide supports pointing the causal arrow in that direction specifically.
We know obese people eat more, and we know that the greater fat mass has greater nutritional requirements.
The interesting question is not whether 400 calories are associated with the weight gain, clearly people are more obese now and also they eat 400 more calories on average, no one is disputing this. The interesting question is whether those 400 calories cause the weight gain or are caused by the weight gain. You are implying the former but there is not a lot of evidence in support of it—and other posters in this thread are chiming in with other evidence suggesting that 400 calories daily is well within normal historical variation, which is SMTM’s point that “400 extra calories causes weight gain” would be weird.
I think we are getting caught up in the definition of “small”. My original point earlier is that 400 calories is small compared with historical variation and variation among humans. Your original point is that 400 calories is more than enough to explain the weight gain and thus isn’t “small”. Those are different definitions of small, and are both true: 400 calories is small compared with historical and present variation among humans AND 400 calories is enough to explain the extra weight.
But the latter is obvious; clearly those 400 calories explain the weight gain, because people aren’t suddenly metabolizing air or water or other calorie-free inputs into extra weight, those fat cells are creating fat from calories people consume. I suspect people are ascribing other claims to you because “400 calories is not small—it’s enough to explain the excess weight” is only a useful claim in this context (“this context” being “what causes obesity?”) if you are also making the causative claim.
You insist you are not making the causative claim—so what exactly are you arguing re: the question of “what’s causing the weight gain?”