Fastest drinker : 640 mL in 3.17 seconds Or 201.9 mL/s, which is 726813.9 mL in an hour, which is 726.8 liters per hour. (Zhang Fenzhong, Guinness World Records) There are about 2600 kilo calories in a liter of canola oil (which is one of the cheapest and densest easily digestible foods). Since the liters/hour I cited above are derived from a world record holder, I will reduce the estimate to 300 liters/hour to account for lack of drinking ability in fats, bathroom breaks, time needed to catch one's breath, and the higher viscosity of oil vs beer (which Zhang drank to obtain his record). So, my calculations are: 300 L/h * 2600 kcals/L * 15 waking hours in a day = 11,700,000 kilo calories per day. A 5'5", 25 year old female would need to weigh approximately 2600000 lbs or 1179340.16 kgs to require 11,700,000 kcals per day (per "http://www.bmi-calculator.net/bmr-calculator/") Sooooo, yeah. No real upper limit there. Another possibility is the limitations imposed by our inefficient digestive systems. BUT... I am unable to find data for that calculation.