To maximize weight gain, sumo wrestlers follow a regimen designed to slow metabolism.
a few tips from a sumo...
Don't eat breakfast. Breakfast jump-starts your metabolism! Skipping this important meal tells your body that you may be in a famine state, and prompts it to burn fewer calories throughout the day.
Exercise on an empty stomach. Our bodies are uniquely designed to conserve energy when fuel (food) is not available. This feature allowed our ancestors to survive when they didn't have access to enough food yet still needed to be active for hunting - or running from predators.
Eat before bed. Sleeping on a full stomach can allow your body to store the nutrients absorbed more easily (in the form of fat). Most importantly, when we eat late we tend to overeat. This can be because we are late-night snacking, are over-tired, or we waited so long to eat we have a hard time stopping once we get started.
Eat large portions. Eating until you are stuffed at each meal, rather than only until you are satisfied, can pack hundreds of extra calories each day. 3,500 calories consumed above the amount you burn is equivalent to 1 pound, so eating 350 extra calories each day (1 donut, 2 pints of beer...) can add up to 1 pound of excess weight in only 10 days - or 37 lbs in a year!