Whether you are a health nut, fitness freak, pro athlete or just a health conscious parent you have looked at the odd foot label or two right?
You probably count the total calories per serving for many foods that you eat, happy when you make clean choices, have you ever wondered though, whether with the help of a guide or not how the calorie value of the food is calculated?
If you are wondering this, then you have most likely investigated further wondered how on earth 1g of protein and 1g of carbs equals 4 calories but 1g of fat equals 9 calories and even more strange is how they manage 100 calories in those 100 calorie snack packs.
How energy in food is determined is one of life’s mysteries but there is a pretty simple method behind it, to work out how a calorie is determined, it helps to define a calorie.
A calorie is basically a measure of energy, it is the amount of energy required to raise the temperature of 1g of water 1 degree celsius. This isn’t what you see on food labels however. the calorie (take note of the capital C) you see on packets is actually a kilocalorie (kcal) or 1,000 calories which is enough energy to raise 1kg of water 1 degree celsius. You don’t need to count calories and multiply by 1,000, this info is just to confirm the science and the different versions and meanings of the word, bear in mind we are talking about food. We are talking about calories or kilocalories.
So how are food calories you consume determined? The original method called ‘bomb calorimetry’ meant placing a piece of food into a sealed container surrounded by water and igniting the food until it all burned up. The heat emitted by the food would cause a water temperature rise, scientists could then measure the change in water temperature to calculate the amount of calories in the food, using this method the following values were calculated from the macronutrients:
This may seem like more than you see on packets, that is because bomb calorimetry is accurate measure of the total calorie content in food, however it overcalculates the amount of usable energy in food, since the absorption and digestion rates of nutrients vary in human beings.
When you look at a food label – 4 kilocalories for carbs, 4 kilocalories for protein and 9 kilocalories for fat are basically indirect calorie estimations made using the Atwater system, a conversion system named after it’s creator, Dr. Wilbur Olin Atwater.
This method takes into account the gross energy value, apparant digestibility coefficient and urinary correction of a food source to provide a pretty accurate measure of macronutrients that exist to date. Example, dietary fiber reduces the percentage of food that is usable by the body for energy production, the fiber component is therefore deducted from the total carbs before calculating calories. This is why we are familiar with 4 kilocalories per 1g of carbs rather than 4.2 kilocalories. There are some limits to this method and mild variations in food content but the values are pretty accurate overall.
The ‘4-9-4’ method or Altwater system is how the caloric content of foods is determined today. As an example, food with 20g of carbs, 4g of fat and 6g of protein contains around 140 kilocalories.
Now you should realise how calories in all of your favourite foods is determined the next thing to wonder is are the labels on these foods accurate?
The journal of the American Medical Association published a study which showed that the actual caloric content in packaged foods differed by as much as 25% to what was printed on the label.
The Tufts University of Boston, Massachusetts looked into the food label accuracy of restaurant foods and frozen meals, researchers found that some foods contained twice the amount of calories that were stated and the average calorie count of frozen meals was 8% higher than displayed on the label.
A report has also been published by the National Institute of health which showed calorie content in popular energy-dense snack foods in America to be a bit higher than stated on the label.
Although a few studies have found calorie count on label to be inaccurate, the mistakes are often small and shouldn’t be of concern. To ensure complete accuracy of foods, weigh them out in grams or ounces rather than the approximate serving sizes printed on labels and be consistent with label tracking. Even if the numbers are a bit off, if you consistently track your calories you can make little changes in what you eat to help you reach a desired weight.
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