Calorie Consumption

If you ever find yourself talking to a know-it-all chemist about nutrition, they will almost certainly point out the common error related to the calorie: that almost everyone who talks about calories is doing it wrong. A calorie (lower case ‘c’) is a chemistry unit of energy.

When normal folks (and believe me, chemists are not normal) talk about ‘calories,’ we are generally referring to what a chemist would call a ‘kilocalorie,’ or what scientists often call a ‘large calorie’ or ‘food calorie’, equivalent to 1000 chemistry calories. It makes little difference, but to be proper, I will use a capitalized ‘Calorie’ to talk about Calorie consumption, since this has become the accepted shorthand for people who sweat the small stuff. If a know-it-all chemist ever gives you attitude about it, at least you know enough now to shove it back in their face.

Calories are a measurement of food energy. Food is made up of many nutrients, but only a few nutrients contain Calories and give you energy. The big three are fats, which contain 9 Calories per gram; and carbohydrates and proteins, which each have 4 Calories per gram. Consumed Calories in the body are either burned for energy (walking around, maintaining brain and organ function, even breathing burns Calories) or stored. The biggest Calorie storage facility in the body is adipose tissue, better known as fat.

For those looking to lose weight by shedding fat, old-school diet wisdom has a simple equation: burn more Calories than you take in. Figures vary by who you ask and what formula you use (do a quick search for “Basal Metabolic Rate” to find more info and Calorie calculus than you could ever want), but most experts recommend that active men consume between 2400-2800 Calories every day and active women get between 2000-2400 Calories daily to maintain a healthy weight. To lose weight, you would either need to consume fewer Calories, burn more Calories through physical activity, or do both to go into ‘caloric debt’.

This simple math is based on the assumption that all Calories are basically the same, that a Calorie from carbohydrates is equivalent to a Calorie from fat or protein. This is the basis of nearly every diet for fifty years in the past century, and it works. To lose a pound of body fat, the body must have a Calorie debt of around 3500 Calories. This is equivalent to walking or running about 35 miles. That might sound like a lot for someone hoping to lose weight at a rate of 2-3 pounds per week, but remember that most caloric debt happens with a combination of increased activity and changes in diet. Walking 4 miles a day will not only burn 400 Calories while you walk, but will increase the number of Calories you burn while you go about your other daily activities. If you cut out 500 additional Calories every day from your normal diet, you can easily drop 2 pounds in a week.

Again, the philosophy and math of caloric debt is the basis of lots of diets from the last century. Since then, attitudes and knowledge about Calories have changed, and the idea that all Calories are created equal has shifted. The best explanation for why the Atkins diet and other ‘low-carb’ diets promote weight loss is a process called ketosis. In a normal body stored carbohydrates rarely run out and dipping into fat stores for energy only happens during prolonged exercise. Low-carbohydrate diets heavily restrict carbohydrates, but not total Calories. This puts participants into a state in which carbohydrates, the default source of energy for the body and brain, are all but absent, and forces the body to use fat stores for activity and normal body processes. Other weight loss diets don’t stress restricting Calorie consumption as much as eating foods less likely to raise blood sugar levels(low glycemic-index foods).

Many of these diets have proven successful at least on a market level, although the scientific jury is still out on this relatively new outlook on Calories. Our picture of nutrition is constantly changing and getting more complex. While our tried and true picture of how Calorie consumption in the body works as a starting point and as a weight loss tool, it is pretty clear that we will need a fuller, more fleshed-out picture of how different kinds of Calories are consumed, broken down, and used by the body to make smart decisions in the future. We may need chemists. Sigh.


Some speculate that he is part man, part animal, but the only thing that you need to know is his obsession and dedication to the art of living lean and helping you to achieve your body fat goals.

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