This seems feasible.
However, human digestion is pretty efficient - the heat of combustion of starch is ~ 4.2 Calories (kilocalories) per gram, which compares pretty well to the usually quoted 4 Calories per gram of carbohydrates for dietary purposes. (Fats are usually quoted at 9 Calories per gram, so fat storage is also pretty efficient. Not quite as efficient as, say, propane, but really quite good.)
Where you can get significant improvements isn't so much in the extraction of energy as in the use of that energy. The way humans (and other mammals) do endothermy is very energy-hungry.
Also, humans eat several times a day, but the amounts are rather small. Plenty of animals are capable of eating huge quantities relative to their own body weight. According to the USDA chicken meat is on the order of 200 calories per 3 ounces: http://www.fsis.usda.gov/shared/PDF/Chicken_Turkey_Nutrition_Facts.pdf
That's about 1000 calories per pound. So if your creature can eat 20 pounds of meat at a meal, that's 20,000 calories - which is the equivalent of 8-10 days of activity even at 2000-2500 calories/day for a human.
The combination of these two is why some large snakes can go months between large meals. You probably can't go quite as low metabolically as a snake for an intelligent species (brains are very energy-hungry), but assuming they evolved in a very stable thermal environment they might need much less energy for maintaining body temperature.