According to Tomonosuke TAKASHIMA, Saigo was overweight because he lost a lot of weight when he took refuge at Oshima, and almost died en route to Oki-no-erabujima island, so the truth might be that he started to gain weight when he was in zashikiro because of lack of exercise at the latter end of his stay on Oki-no-erabujima island.
高島鞆之助の言では西郷は大島潜居の頃から肥満になったとしているが、おそらく沖永良部島流罪当時は痩せこけて死にそうになっていたというから、沖永良部在島後半期に座敷牢にいて運動不足から肥満し始めたというのが真相だろう。