Most North Americans carry a nice supply of emergency calories around the middle. Until that supply has been depleted I really don't worry about energy levels or calorie intake. My uncle on the other hand is built like a professional bicyclist and eats small amts of calorie dense foods every 45 minutes.

After 4 weeks in a warm climate I have probably lost 10 pounds and the calorie intake jumps to around 5k a day.

Have I ever lost too much weight? Yes, 9 days of bananna pudding poo accompanied by gas while hurling your carcass up and over 12-14000 foot passes will do that to you. Managing food intake at high elevations 10k+ is a beast. Eat -ANYTHING- and the energy level in the legs drops to nothing as the body shifts resources to the gut.