Perhaps his success at records was just his ability to constantly fuel. It's suggested his caloric intake could be greater than his caloric burn during ultras. He was a feaster.
The following excerpts are taken from Dr. Tim Noakes' "Lore of Running" pages 352 and 353 where he discusses Kouros' 1985 960km Sydney to Melbourne race ( which he won ).
His daily energy expenditure ranged from 15,367 Kcal on the first day to 7,736 Kcal on the fifth day, and his daily energy intake varied from 13,770 Kcal on the first day to 7,800 Kcal on the fifth day. Overall, his total estimated energy intake ( 55,970 Kcal ) exceeded his energy expenditure ( 55,079 Kcal ).
To maintain this high rate of energy consumption, Kouros ate every 15 minutes...
Carbohydrates provided 96% of his total energy intake.
Clearly, two factors contribute most significantly to Kouros' success. First, he has a remarkable ability to go without sleep for prolonged periods. Second, he has a capacity to maintain a high rate of energy consumption during these races. This parallels findings in cyclists competing in the formidable Tour de France. Only those cyclists whose rates of daily energy consumption equal their rates of energy utilization are able to finish the race."