Calories: What are they?

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Let's start with what a calorie is and how we know. How many calories of food contains a calorie is a unit of measure like an inch or a kilogram only instead of measuring length or wait a calorie measures energy. Technically a calorie is the amount of energy it takes to raise one gram of water by one degree celsius. Calories can be measured using something called a bomb calorie meter. Isn't that name. You might even have built a crude version of a bomb category meter in sixth grade science class. In broad strokes submerge in a bucket of water. And you put a thermometer in the water and then inside that submerged chamber you set something on fire. The heat generated by the combustion raises the temperature of the water in the bucket. And you can measure that with the thermometer. And then you can calculate the amount of energy or calories were in the thing that you said on fire so we used to use bomb calorimeters to calculate how many calories a given food contains these days. However it's much more common to estimate. The number of calories based on how much protein fat and carbohydrate food contains and those amounts can be determined through chemical analysis. Now when we're using the word calorie in relation to food by the way we are actually referring to kilocalories. Sometimes you'll see calories abbreviated as k cow. And that's what that refers to when we say that a food contains sixty calories. It really contains sixty thousand calories but all those zeros would be a pain to deal with. So just lop them off and believe me. This drives physicists. chemists absolutely nuts that. Why do we need to know how many calories food contains well when we they just food. We don't literally set it on fire in our stomachs but our bodies do release it's stored heat or energy and then we either use that energy to power our biological processes or if we've taken in more energy than we need we store it for future use if we habitually in more energy than we use we gain weight so we use calories as a guideline to determine how much food energy a person needs. We need enough to fuel growth and maintenance but not so much that we start storing a lot of fat there are calculators. I'm sure you've seen them. They can estimate your daily calorie needs taking into account your age sex height of activity level and then there are databases and labels to tell you how many calories are in foods however as james implies in his question. There are few problems with this system. First of all those calorie needs estimates. Can be way off. You can plug your details into an online calculator and be told that you use eighteen hundred and forty seven calories per day but look you need to take that number with a truckload of salt. Energy expenditure varies hugely from person to person. Even if you. And i are the exact same height weight age and sex and we do the exact same workout. You could burn four hundred calories more or less than i do. Every day and energy needs can also be affected by genetics body composition hormones drugs and a million other factors and moving targets and just to make the whole situation just a little bit more ridiculous. Those readouts on your treadmill peleton fit. Watch or diet tracker that. Tell you how many calories you burn doing. Various activities are only slightly more accurate than asking the magic eight ball. But wait. there's more calorie counts for foods are also not as reliable as you think those numbers that are listed in your calorie counting app represent average values foods so even if you are measuring or weighing your food with great precision well. This apple may be a little bit sweeter than average. That banana might be a little less ripe. This not might have a little bit more fat. Even for packaged and processed foods. The calorie count. That's shown on the nutrition. Facts label is just an average of variation of plus or minus. Ten percent of that value would not be at all surprising. Secondly those calorie counts are estimated using formulas that may or may not be one hundred percent reliable it was recently discovered for example but the standard formulas that were in use for most of the last hundred years. Were overestimating the amount of energy that we humans are great from nuts. More modern methods suggests that owens for example provide about twenty percent less energy or fewer calories than we previously thought

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