Human beings are the most intelligent form of life on Earth and, as far as we know, the only sentient beings in the Universe. From the neck down, however, we aren't much different from bears or raccoons--we're omnivores--we can eat just about anything and turn it into energy or, alas, if we eat too much, fat.
Notwithstanding our complexity, and regardless of our aspirations, at the most fundamental biological level we're not all that different from a rubber bag. Every day we take in some food and water, burn some amount of energy to sustain us, and dispose of the waste that's produced in the process. If we take in more than we burn and dispose of, the rubber bag expands: we get fat. If we burn and dispose of more than we take in, the rubber bag contracts: we lose weight.
From an engineering standpoint this is a simple system. We have virtually no control of what comes out; that's just the waste products of the factory. We have little effective control over what we burn: in theory our bodies are at our command but the constraints of modern life sorely limit the extent we can exercise.
Consequently, the only real control we have is over what goes in: what, when, and how much we eat. Weight control can be reduced to a very simple matter of arithmetic. Total the number of calories in the food you eat per day, averaged over a period of time. Take the number of calories you burn per day, roughly the same for everybody of your sex, height, build, and level of activity. Subtracting the calories burned from the calories eaten gives excess calories per day. This number times thirty is excess calories per month. A pound of fat is equivalent to about 3500 calories. If you eat 3500 calories more in a month than you burn, you'll gain a pound that month. If you burn 3500 calories more than you eat, you'll lose a pound. All the weight you gain or lose is the consequence of these simple numbers.
The most advanced racing engine is, basically, an air pump. Humans, notwithstanding our pretensions of transcendence are, at a comparable level, water pumps. Every day, the quantity of water we take in and dispose of dwarfs the other physical interactions with our environment. This means that day to day weight figures primarily measure only how much water happens to be inside the rubber bag at the moment. They're of no use in managing one's health. Instead, it's necessary to extract the signal from the noise, the reality from the raw data. Learning how to do this and applying that information to controlling your weight will be discussed in chapter .
By John Walker