Comment by carabiner
11 hours ago
Hypothesis is that the irishmen were doing hard physical labor that required a high caloric intake. PCT thru-hikers consume 4,000-4,500 calories per day (at least I did) while staying thin. According to inter-net, 13 lb of potatoes has about 4,500 calories. Apparently US civil war soldiers expended 3-4k per day.
I was responding to the claim by @codeableconcept that the absence of significant dietary fat somehow prevents obesity, independent of energy balance. That seems unlikely.
Obviously it's possible for an active man to expend ~4500 kcal/day. I've done it myself many times. Even back during the Civil War, US soldiers typically consumed more energy dense food and only got a fraction of their calories from potatoes.