In cellular respiration sugars are oxidized and the resulting energy is stored in molecules of ATP. Each gram of sugar produces about 3.75 kilocalories or 16 kilojoules of food energy. The average human body utilizes about the same energy as a 100 watt light bulb. 100 watts x 24 hours x 3600 seconds/hour = 8,640 kilojoules per day.

If we got all our energy from sugar and starch, we would need about 540 grams/day which is just over 1 pound per day. (Starvation is considered to be less than 1800 kilocalories or 6,830 kilojoules per day.) What does the energy locked in 1 gram of sugar, 16 kilojoules, look like? Let's oxidize a gram and see.

If we could power our bodies with electricity from the utility it would take 2.4 kilowatt hours to operate at 100 watts for a day. At the rate of about 10 cents per kilowatt hour, the energy would cost 24 cents.