Q. How are the calories on food packages figured?

Newton

A. That's a timely question, because a lot of folks will pack in a lot of calories during the holiday season.

A calorie is the amount of energy (calor means heat in Latin) it takes to heat one gram of water one degree Celsius. But how do we figure how many units of heat energy are in a candy bar or can of soup?

For that, you can thank Wilbur Olin Atwater, an American chemist credited as the first scientist to apply chemistry to agriculture. In the 1890's he developed a calorimeter to measure the calories in the components of foods -- carbohydrates, proteins, fats. He heated them with a known quantity of energy and measured how much heat was produced.

Atwater also figured that some of the energy in the food we eat never gets absorbed in the body; it's lost in our solid and liquid waste. With his calorimeter he measured how much of what goes in, stays in, and how much comes back out. With those adjustments, known as Atwater factors, we know that when we eat 1 gram of carbohydrates we absorb 4 calories; 1 gram of protein, 4 absorbed calories; 1 gram of fat, 9 absorbed calories.

Manufacturers know how much of each component a food product contains, so the calorie number on the package is: grams of carbohydrates X 4; grams of protein X 4; grams of fat X 9.

For those who take in alcohol, multiply grams consumed times 7 for your caloric intake.

See you in the gym in January.