The answer is soup. Not just any soup, of course, but a high protein, body building broth. This is consumed alongside quantities of rice and pickles, frequently accompanied by beer and possibly augmented by the odd side dish of hamburgers (fast food being by no means prohibited). Known as chanko-nabe, or "dad's pot", the broth is a sturdy concoction based on chicken, fish or beef to which is added a vast variety of ingredients such as cabbage, burdock, radish, potato, chrysanthemum and lotus roots. The circumference-enhancing dish is effective simply because of the amount devoured by the rikishi, the sumo competitors, who claim to eat just twice a day - and then spend large amounts of time sleeping off their heavy meals.
You can sample something of the sumo life in Tokyo. The capital contains more than 50 sumo beya where the rikishi train and live until they marry - there is a high concentration of these establishments in the Ryogoku area, near the sumo wrestling stadium. At most sumo beya, visitors can watch morning training sessions, provided they show due reverence and maintain strict silence. Some time around 8am on weekdays you simply ring the doorbell of a sumo beya, bow politely when you are let in by a junior wrestler and wordlessly follow him to a large room where several of the inmates, clad only in loin cloths, train in a big sanded area. Seated (very) quietly on a platform, you watch the rikishi taking each other on two by two, attempting to force the opponent to the ground or push him out of a five-metre ring as in a formal contest. The other wrestlers stand on the sidelines shouting occasional words of encouragement and limbering up by slapping their thighs or performing alarming and thunderous bunny hops.
When the rikishi disappear to consume their first feast of the day, you can do likewise by searching out a chanko-nabe restaurant. Named after a former wrestler and sumo beya owner, Tomoegata in Ryogoku is one such outlet. Here you tuck into hearty, and very tasty, helpings of soup with accoutrements, choosing portions supposedly sized according to sumo rank. Having filled up on just the one bowl of broth you can then wander over to the sumo stadium's small museum and check out the portraits of the grand champions, a range of 68 dating from 1624 to the present day - when the reigning victor harks not from Japan but Mongolia.
To visit a sumo beya consult the Japan National Tourist Organization (see page 8) where appropriate lists and maps can be provided. The Sumo museum at the Sumo stadium, 1-3-28 Yokoami, Sumida-Ku (00 81 3 3622 0366; www.sumo.or.jp) is open weekdays, 10am-4.30pm. Entrance is free and an English-language booklet is provided. Tomoegata Ryogoku Restaurant is at 2-17-6 Ryogoku, Sumida-ku (00 81 3 3632 5600; www.tomoegata.com - in Japanese only). The lunch menu ranges from Y1,150 (pounds 5.90) for a junior meal to Y1,470 (pounds 7.50) for a top-ranking meal