When monitoring weight, many people calculate the calories of food to track their energy intake, according to a study by Journal of the American Journal of Clinical Nutrition.. But what exactly are calories, why are they calculated, and how do food scientists determine if a granola bar is 100 or 300 calories?
What are calories?
NS calorie Is a unit of energy, not a measure of body weight or nutrient density. However, the calories displayed on the nutrition label are actually kilocalories, or kcal. United Kingdom National Health Service (NHS) UK..Food packaging always mentions kcals, even though it’s just saying “calories”. 1 kcal is the amount of energy required to heat 1 kilogram of water once. Celsius (2.2 pounds of water at 1.8 degrees Fahrenheit), said Grace DeRocha, a registered dietitian and health coach at the Blue Cross Blue Shield in Michigan.
Related: What if I eat only one type of food?
Calculate calories with a bomb calorimeter
In 1990, the U.S. government Nutrition Labeling Education Act, Standardized information including calories that nutrition labeling must disclose. This means that food scientists need to measure their key nutrients and calories before US packaged foods are on the shelves. One way to do this is to use a tool called a bomb calorimeter.
Ruth McDonald, a professor and chairman of food science and human nutrition at Iowa State University, said the tool directly measures the amount of energy contained in food. To use this tool, scientists place the food in question in a closed container surrounded by water and heat it until the food is completely burned out. Scientists then record the rise in water temperature to determine the calorie count of the product.
However, the bomb calorimeter is not the only way to measure calories. Food scientists also rely on calculations developed by the 19th century American chemist Wilbur Atwater. Wilbur Atwater has decided on a method to indirectly estimate the calorie count of food.
4-9-4 Calculate calories with the system
Atwater introduced this technique, known as the 4-9-4 system. This is because calorimeters do not take into account the loss of calories by humans passing through heat, urine and feces. Live science previously reported.. Atwater overcame this limitation by calculating the number of calories in various foods and testing feces to see how many calories were excreted. His experiments revealed a 4-9-4 system, with protein and carbohydrates each about 4 calories (0.04 ounces) per gram and fat 9 calories per gram. He also found that alcohol is 7 calories per gram.
“Let’s say you have food that contains 10 grams [0.35 ounces] Protein (10 x 4 = 40) and 5 grams [0.2 ounces] For fat (5 x 9 = 45), the total calorie value is 40 + 45 = 85 calories, “McDonald’s told Live Science by email.
Related: What is metabolism?
But even if food scientists modernize Atwater’s calculations, some experts say the Atwater system is outdated and inaccurate.2012 study published in American Journal of Clinical Nutrition We have found that the energy content of certain foods, such as nuts, cannot be calculated accurately by the Atwater system.In addition, the FDA 20% margin of error For nutrients listed on food labels that contain calories, these calorie counts mean they are not incredibly accurate.
But even if there is no margin of error in the calorie label,[this method] Does not consider Digestion process“But we assume that nutrients are completely converted into energy. Our bodies are fairly efficient at recovering energy from food, but that doesn’t happen in humans,” McDonald’s said. rice field.
For now, the calorie count of a cup of granola bar or instant noodles is likely to have been calculated using the classic Atwater system, but in the future that method may be abolished. I have.
Why do people count calories?
The calorie data provided in food packaging allows people to calculate their personal intake. According to the NHS, this can be useful information to prevent people from consuming too much.
Some foods, such as protein and fat, feel full faster than foods, such as carbohydrates. According to the NHS, this can mean that a protein-rich diet burns less calories than a carbohydrate-rich diet, even though it is just as full. By quantifying the energy in food, consumers can get a better idea of the energy they are supplying to their bodies.
Exercise calorie calculation
Exercise monitoring devices, such as treadmills and fitness trackers, typically display “live” data on the number of calories burned by an individual per exercise session. These devices do not display the total number of calories burned by the body during that time, but they do display an estimate of the number of calories burned solely due to physical activity. According to an article published in, these devices incorporate personal facts into their algorithms to estimate calories burned. Journal of Parallel and Distributed Computing 2018. This includes age, gender, height and weight.
From this information, smart devices can estimate a person’s BMR (basal metabolic rate). This is the amount of energy the body consumes while resting and performing its daily biological functions. Encyclopedia of animal cognition and behavior..
How to calculate calories: behind science
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