Calories are a measure of energy and can be used to describe any fuel, from petrol to bread. One calorie is the amount of energy required to raise the temperature of one gram (0.035 ounces) of water by one degree Celsius (1.8 degrees Fahrenheit).
Food labels often quote energy content in kilocalories (kcal), because food is so rich in energy that it makes more sense to label 1,000 calories at a time. This means a biscuit labelled as having ‘100 calories’ actually has 100,000 calories, and can raise the temperature of one kilogram (0.
45 pounds) of water from freezing to boiling point.
The number of calories in any given item of food is calculated by measuring how much energy is released when a substance is burnt. Inside our bodies, molecular machinery is responsible for burning the fuel we eat, but in the lab, using a spark gives the same result.
The traditional method of calorie calculation is to put the food inside a sealed unit known as a bomb calorimeter. The food is surrounded by an atmosphere of oxygen to ensure it will burn well, and the container is then sealed and surrounded by a known volume of water.
A spark ignites the food inside and allows it to burn until it is reduced to charcoal, releasing all of the energy contained inside. The energy is converted to heat, which in turn raises the temperature of the water.
By measuring the water’s temperature change, you can then find out exactly how much energy has been released, and calculate the calories from there.
Today, many food manufacturers use a different system to create nutritional label; instead of burning the food item whole, they simply add up the calories of the different components, such as fats, carbohydrates and proteins.
Calculating calories – step 1
Calculating calories – step 2
Calculating calories – step 3
Sugar contains empty calories
The amount of energy in an item of food or drink is measured in calories.
When we eat and drink more calories than we use up, our bodies store the excess as body fat. If this continues, over time we may put on weight.
- As a guide, an average man needs around 2,500kcal (10,500kJ) a day to maintain a healthy body weight.
- For an average woman, that figure is around 2,000kcal (8,400kJ) a day.
- These values can vary depending on age, size and levels of physical activity, among other factors.
- Check if you're a healthy weight by using our body mass index (BMI) calculator
Our bodies need energy to keep us alive and our organs functioning normally.
When we eat and drink, we put energy into our bodies. Our bodies use up that energy through everyday movement, which includes everything from breathing to running.
- To maintain a stable weight, the energy we put into our bodies must be the same as the energy we use through normal bodily functions and physical activity.
- An important part of a healthy diet is balancing the energy you put into your bodies with the energy you use.
- For example, the more physical activity we do, the more energy we use.
If you consume too much energy on 1 day, do not worry. Just try to take in less energy on the following days.
Knowing the calorie content of food and drink can help ensure you're not consuming too much.
The calorie content of many shop-bought foods is stated on the packaging as part of the nutrition label.
This information will appear under the “Energy” heading. The calorie content is often given in kcals, which is short for kilocalories, and also in kJ, which is short for kilojoules.
A kilocalorie is another word for what's commonly called a calorie, so 1,000 calories will be written as 1,000kcals.
Kilojoules are the metric measurement of calories. To find the energy content in kilojoules, multiply the calorie figure by 4.2.
- The label will usually tell you how many calories are contained in 100 grams or 100 millilitres of the food or drink, so you can compare the calorie content of different products.
- Many labels will also state the number of calories in 1 portion of the food.
- But remember that the manufacturer's idea of 1 portion may not be the same as yours, so there could be more calories in the portion you serve yourself.
- You can use the calorie information to assess how a particular food fits into your daily calorie intake.
There's a wide range of online calorie counters for computers and mobile phones. Many of these can be downloaded and used for free.
- The NHS cannot verify their data, but they can be helpful to track your calories by recording all of the food you eat in a day.
- Some restaurants put calorie information on their menus, so you can also check the calorie content of foods when eating out.
- Calories should be given per portion or per meal.
- Find out more about food labels
The amount of calories people use by doing a certain physical activity varies, depending on a range of factors, including size and age.
The more vigorously you do an activity, the more calories you'll use. For example, fast walking will burn more calories than walking at a moderate pace.
- Find out how the body burns calories in
- If you're gaining weight, it could mean you have been regularly eating and drinking more calories than you have been using.
- To lose weight, you need to use more energy than you consume, and continue this over a period of time.
- Get used to counting calories and use our calorie counter
- The best approach is to combine diet changes with increased physical activity.
- Find out how much physical activity you should be doing
- Find out how to make healthy changes to your diet and lose weight
- If you need help losing weight, why not try the free NHS 12-week weight loss plan.
Good Question: How Are Calories Measured In Food?
MINNEAPOLIS (WCCO) — A McDonald’s Big Mac has 540 calories and a Panera Bread Frontega Chicken sandwich has 740. By the end of 2016, the FDA will require larger chain restaurants, fast-food places and some business that sell food to post this calorie information.
So, Chris from Madison asks: How are calories measured in food? Good Question.
Calories are a measure of energy. Technically, one calorie is the amount of energy it takes to raise one gram of water one degree Celcius. Food is measured in kilocalories, so it’s actually 1000 calories for every 1 calorie listed.
“There are actually a couple of ways this can be done,” says Holly Willis, director of dietetics and nutrition at St. Catherine University.
First, the food can be sent to a laboratory to be analyzed through a number of mechanisms.
“They would ask for a full sample of, say, chicken chipotle sandwich,” says Willis. “They’re going to mix it up into a pulverized version of that, take a small sample out and then they’ll take an analysis.”
Sometimes, scientists will burn the food in a bomb calorimeter to measure how much energy the fats, proteins and carbohydrates give off. This can be calculated by measuring the temperature change to determine how much energy is in the food.
“The easier way would be to do a manual calculation using food databases,” says Willis.
The U.S. Department of Agriculture maintains a public database where nutrients and calories can be calculated. With this system, you would look up every single ingredient in a food and add up the nutrients that contain energy. Proteins and carbohydrates are 4 kcal/gram and fats are 9 kcal/gram.
The FDA requires restaurants and businesses to take “reasonable steps” to make sure their calorie counts are what they say. A study in the Journal of the American Medical Association found they were accurate overall, but did find 20% of foods went over by 100 calories.
How is the caloric value of food determined?
A very good question to tackle because many people do not have a good understanding of calories. First of all, a calorie is not a thing and therefore cannot be full or empty. You cannot put calories in a bottle. A calorie is a unit of measure of energy.
Very specifically, it is the amount of energy that is required to raise the temperature of one mL, (which is also one gram), of water by one degree Celsius. If you really want to be a stickler for detail, it is the energy needed to raise the temperature from 14.5 to 15.5 degrees C.
The word calorie was actually coined by the great French chemist Antoine Lavoisier who used it to refer to the body’s internal heat.
A food calorie is actually a “kilocalorie.” In other words it is the amount of energy needed to raise the temperature of one liter of water by one degree. Originally, the calorie content of a food was measured in a calorimeter.
A known amount of food, which has had its water content evaporated, was placed in a container surrounded by a known amount of water. The container was sealed, oxygen piped in, and the food ignited.
From the rise in temperature of the water, the calorie content of the food was calculated.
There were problems, however with this sort of calorie determination. Food can contain components such as fiber that will burn in a calorimeter but are not absorbed into the bloodstream and therefore do not contribute calories.
Today, producers use the “Atwater indirect system” to calculate calories by adding up the calories provided by the energy-containing nutrients: protein, carbohydrate, fat and alcohol.
Because carbohydrates contain some fiber that is not digested and utilized by the body, the fiber component is usually subtracted from the total carbohydrate before calculating the calories.
The Atwater system uses the average values of 4 Kcal/g for protein, 4 Kcal/g for carbohydrate, 9 Kcal/g for fat and 7 Kcal/g for alcohol that were determined by burning these substances in a calorimeter.
(There is some rounding off because simple sugars provide somewhat less and polysaccharides somewhat more than 4 Kcal/g).
Thus the label on a 45 gram KitKat that contains 3 g of protein, 29 g of carbohydrate (22 grams of which are simple sugars) and 12 g of fat would read 230 Calories.
Some interesting data emerges from such calculations. The calorie content of a doughnut, about 450 Kcal is found to be close to that of a stick of dynamite. The difference of course is that the energy from the dynamite is released instantly when ignited, while the doughnut releases its energy content in the body more slowly. So you don’t blow up from a doughnut. Not literally anyway.
How Are Calorie Counts Calculated?
Counting calories is one of the main techniques people use when trying to lose weight. But what exactly are calories, and how do food scientists determine whether a granola bar has 100 or 300 calories?
A calorie is a unit of energy, not a measure of weight or nutrient density. The calories you see on nutrition labels, however, are actually kilocalories, or kcals. Food packaging always refers to kcals, even though it just says “calories.
” One kcal is the amount of energy required to heat 1 kilogram of water by 1 degree Celsius (2.2 lbs. of water by 1.8 degrees Fahrenheit), said Grace Derocha, a registered dietitian and health coach at Blue Cross Blue Shield of Michigan.
Calories in our food all come from one of the three macronutrients: fat, carbohydrates and protein, Derocha told Live Science. [What If You Ate Only One Type of Food?]
In 1990, the U.S. government passed the Nutritional Labeling and Education Act, which standardized the information, including calories, that nutrition labels must disclose. That means that before any packaged food in the U.S. hits the shelves, food scientists have to measure its macronutrients and calories. One way to do this is with a tool called a bomb calorimeter.
This tool directly measures the amount of energy that a food contains, said Ruth MacDonald, professor and chair of food science and human nutrition at Iowa State University.
To use this tool, scientists place the food in question in a sealed container surrounded by water and heat it until the food is completely burned off.
Scientists then record the rise in water temperature to determine the number of calories in the product.
But bomb calorimeters aren't the only way to measure calories. Food scientists also rely on a calculation developed by the 19th-century U.S. chemist Wilbur Atwater, who determined a way to indirectly estimate of the number of calories in food products.
Atwater introduced this technique — known as the 4-9-4 system — because calorimeters don't take into account that humans lose some calories through heat, as well as by passing urine and feces, Live Science previously reported.
Atwater overcame this limitation by calculating the number of calories in different foods and then testing poop to see how many calories were expelled. His experiments revealed that proteins and carbohydrates each have about 4 calories per gram (0.
04 ounces) and fats have 9 calories per gram, hence the 4-9-4 system. He also found that alcohol has 7 calories per gram.
“Let's say you have a food that contains 10 grams [0.35 ounces] of protein (10 x 4 = 40) and 5 grams [0.2 ounces] of fat (5 x 9 = 45), then the total caloric value is 40 + 45 = 85 calories,” MacDonald told Live Science in an email.
However, even though food scientists have since modernized Atwater's calculation, some experts say that the Atwater system is outdated and inaccurate.
A 2012 study published in the American Journal of Clinical Nutrition found that the energy content of certain foods, such as nuts, cannot be accurately calculated by the Atwater system.
Plus, the FDA allows for a 20 percent margin of error for nutrients listed on a food label, including calories, meaning that these calorie counts aren't incredibly accurate.
But even if the calorie label had no margin of error, “[this method] does not take into account the digestive process, but assumes complete conversion of nutrients to energy,” Macdonald said. “That doesn't happen in humans, although our bodies are pretty efficient at recovering energy from food.”
What are calories? How are they measured in food?
A calorie is a unit of energy. We tend to associate calories with food, but they apply to anything containing energy. For example, a gallon (about 4 liters) of gasoline contains about 31,000,000 calories. You could drive a car 22 miles (35 km) on the calories in 217 Big Macs.
Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit). One calorie is equal to 4.184 joules, a common unit of energy used in the physical sciences.
Most of us think of calories in relation to things we eat and drink, as in “This can of soda has 200 calories.” It turns out that the calories listed on a food package are actually kilocalories (1000 calories = 1 kilocalorie).
So that can of soda actually has 200,000 calories (but don't worry, the same applies to exercise — when an exercise chart say you burn 100 calories jogging a mile, it means 100,000 calories).
A food “calorie” is sometimes capitalized to show the difference, but usually not.
Human beings need energy to survive — to breathe, move, pump blood — and they acquire this energy from food. The number of calories in a food is a measure of how much potential energy that food possesses.
A gram of carbohydrates has 4 calories, a gram of protein has 4 calories and a gram of fat has 9 calories. Foods are a compilation of these three building blocks.
So if you know how many carbohydrates, fats and proteins are in any given food, you know how many calories, or how much energy, that food contains.
If we look at the nutritional label on the back of a packet of maple-and-brown-sugar oatmeal, we find that it has 160 calories.
This means that if we were to pour this oatmeal into a dish, set the oatmeal on fire and get it to burn completely, the reaction would produce 160 kilocalories (remember: food calories are kilocalories) — enough energy to raise the temperature of 160 kilograms of water by 1 degree Celsius.
If we look closer at the nutritional label, we see that our oatmeal has 2 grams of fat, 4 grams of protein and 32 grams of carbohydrates, producing a total of 162 calories. Of these 162 calories, 18 come from fat (9 cal x 2 g), 16 come from protein (4 cal x 4 g) and 128 come from carbohydrates (4 cal x 32 g).
Our bodies “burn” the calories in the oatmeal through metabolic processes, by which enzymes break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids and the proteins into amino acids (see How Food Works for details). These molecules are then transported through the bloodstream to the cells, where they are either absorbed for immediate use or are sent on to the final stage of metabolism, in which they are reacted with oxygen to release their stored energy.