The Science Behind Calories and Nutrition Facts Labels

Have you ever taken a good look at the labels on the bottles, jars, and boxes of food in your kitchen? Then you have probably seen their nutrition labels. These labels provide you with information you need to make healthy food choices.

Our bodies get energy from the food we eat. When we digest food, our bodies use some energy right away and store the rest of the energy for later. Our bodies use energy for three main things. These include digestion, physical activity and other body functions.

Did you know? 

The brain uses up about 20% of the body’s total energy supply!

Ideally, we take in as much energy as we need. If we take in more energy than we need, our bodies will store the extra energy as fat. If we take in less energy than we need, our bodies will get energy from stored fat. Neither too much or too little energy is a good thing. 

A calorie is a measure of energy. The calorie number we see on food labels refers to a kilocalorie (kcal), which is also known as a large calorie or a food calorie. A kilocalorie is 1 000 calories. One kilocalorie is the amount of energy it takes to heat one kilogram of water one degree Celsius at sea level. For foods, the calorie count is a measure of how much energy that food stores in its chemical bonds.

How many calories do you need in a day?

Your age, biological sex, and physical activity levels all affect how many calories you need. For example, a sporty, active person needs more calories than someone who is less active, or sedentary.

Turning the energy from food into energy that the body can use is called metabolism. Metabolism is actually a series of chemical reactions. Each reaction breaks down food and releases energy. 

A person’s basal metabolic rate is the rate at which their body uses energy while at rest. In other words, it’s how much energy your body uses when you are not doing anything. Your basal metabolic rate is responsible for up to 70% of the calories your body uses. 

Did you know? 

Over time, exercise can increase your basal metabolic rate.

What’s in your food?

The nutrition label also gives information about the amount of three main nutrients in the product. These main nutrients are fats (lipids), proteins and carbohydrates.

Some calories you consume every day should come from each of the three nutrients.

Reading nutrition labels can help you determine how much of these key nutrients you are getting from your food. 

How is the fat content of food measured? 

To measure the fat content in a food, the food is ground up and then mixed with a chemical that dissolves only the fat. This method can be long and quite complicated. 

To make the process quicker and easier, scientists are looking at a technique called nuclear magnetic resonance. In this technique, food is bombarded with a pulse of radio waves. This affects the atoms in the molecules that make up the food. Fats react differently to these pulses than other types of molecules. This makes this technique useful for determining the amount of fat in the food.

How is the protein content of food measured?

Since protein is high in nitrogen, by measuring the nitrogen in a food, you can get a good sense of how much protein is in that food. One way to measure the nitrogen in food is through the Kjeldahl method. In the Kjeldahl method, the food is heated in boiling sulphuric acid (H₂SO₄). The acid decomposes the organic molecules and produces ammonium sulphate (NH₄)₂SO₄. Next the ammonium sulphate is distilled with a small amount of sodium hydroxide (NaOH). This converts the ammonium (NH₄⁺) to ammonia (NH₃) gas. The ammonia gas can then be separated and measured using acid-base titration.

How is the carbohydrate content of food measured?

Carbohydrates aren’t specifically measured in food. Instead, they’re calculated. Scientists measure the amount of protein, fat, and water in food. They add these numbers together. Then they subtract that sum from the total weight of the food. The difference is the amount of carbohydrates in the food. 

Why should I read nutrition labels?

By reading nutrition labels, you can ensure that your body is getting the right amount of fats, proteins, and carbohydrates you need to stay healthy. 

Be careful, though. The measures of energy on labels tell you how much energy the food contains. It doesn’t measure how much energy you can actually get from it. That’s because some foods take a lot more energy to digest than others.

Did you know? 

Not all of us get the same amount of energy from the same food. Factors like gut bacteria, enzyme production, and even the length of your intestine can all influence how much energy you get from food!

And of course, it isn’t all about energy. We should also be careful to consume the vitamins we need. These are also listed on nutrition labels.

Of course, different foods affect each of us differently. So while it’s useful to read nutrition labels, it’s also important to pay attention to how you feel after eating certain foods. It’s your body’s way of telling you what it needs!