How true are the calorie values written on food packs? Do different methods of preparation, such as boiling, frying, grilling, etc., change the amount of calories we take in?

The energy we need for our organs to function and to survive our daily activities comes from the foods we eat. A “calorie” is the energy value of a food. One calorie is defined as the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius.

The caloric values of foods are generally known. Food packages bear information about these values, and in some places, the law requires restaurants to list the nutritional values of their meals. However, what is not commonly known is that not everyone receives the same number of calories from the same food. The way the food is prepared or processed influences its chemical structure, and therefore the number of calories it contains. When nutrients pass through the digestive tract, they also undergo a transformation. Billions of bacteria created to help digestion “use up” some of the food’s energy. However, every person has a different digestive system; the precise number of bacteria in each person’s body varies.

For such reasons, people receive different amounts of calories from food, even if they have eaten the same kind of food – and the exact same amount. Calorie calculations without taking these differences into consideration might be mistaken. Even nutritionists cannot calculate definite calorie values without such information. As such, one may not be able to lose weight merely by choosing foods after looking at the information written on packaging.

To begin explaining this, let’s look at how the process of energy consumption works. It starts with the enzymes in our mouth, stomach, and intestines, which are responsible for breaking down complex food molecules into basic building blocks like sugar and amino acids. These building blocks are borne into our cells by means of capillaries. As a result of some chemical processes within the cell, they transform into energy, which is used for carrying out ordinary, everyday actions. The extra calories are stored for later use.

The factors that affect caloric calculations

The calculation of foods’ caloric values began in the 19th century. Scientists developed an approach to approximate the caloric value in one gram of oil, protein, or carbohydrate. Accordingly, a gram of oil gave 9 kilocalories, a gram of carbohydrate or protein gave 4 kcal, and one gram of fibered food gave 2 kcal.

It is not sound logic to assume an average caloric value for foods. The enzymes of the human digestive system are created in such a way that they cannot break fibers down to smaller molecules. These fibers are disposed of when we go to the toilet.

We also eat the bodies, leaves, or roots of hundreds of different plants, be they vegetables or fruits. The cell walls in the body and leaves of some plants are more resistant to digestion than others. In fact, the soundness of the cell walls may vary in different parts of the same plant. Old leaves have more resistant cell walls in comparison to young ones. Generally speaking, if the cells walls are weak, caloric intake will be higher.

The effect of cooking also varies depending on the plant. For example, while the cells of plants like spinach and zucchini are easily broken down, when a plant like water chestnut is cooked, its cells gain a more resistant form. The foods that are not broken down because of their sound cell walls are thrown from our body without proper digestion; thus, it is not possible to absorb all of their calories.

Peanuts, almonds and other types of nuts are digested in a slower and more difficult fashion in comparison to other foods that contain the same level of protein, fat, and carbohydrates. In one study, it turned out that people who ate almonds only got 129 calories, although the packaging claimed they contained 170 calories. Researchers stated that in order to find out the real caloric value of a given food, it is necessary to measure the amount of calories in the urine and waste matter from the bodies of people who have followed the same diet.

There are also explicit differences between foods that can be completely digested. Certain foods, such as honey, are broken down in our stomachs right away. They then join our blood circulation by easily passing through the intestinal walls. For the digestion of fats and proteins however, five-times more energy is required. Proteins need to be broken into amino acids by enzymes so that the energy in them can be used. This point is not taken into consideration when calculating the caloric value written on food packages.

Some foods cause the immune system to be activated because of the pathogenic microorganisms in them. For example, a rarely done piece of meat is a potential danger to our intestinal microorganisms. Even if the immune system does not attack the pathogens in the foods we eat, they still head for the guts in order to recognize whether the alien substance is benign or harmful, and this consumes high amounts of energy. There is no serious study on how many calories the immune system needs to identify an alien substance and, if necessary, neutralize it.

In a research conducted in 2010, one group of people were given sandwiches made from bran bread and cheddar cheese, whereas the others were given sandwiches made from processed cheese and white bread (600-800 kcal). In spite of having consumed the same amount of sandwich, those who ate the sandwiches made from the bran bread and cedar cheese spent twice as much energy in digestion. Therefore, those who consumed the bran bread received 10% fewer calories in comparison to the others. The amount of calories received from foods differs on account of genetic, anatomic, and metabolic differences.

These difference have a serious effect on human nutrition. For example, there can be racial and ethnic differences when it comes to the length of a person’s intestine. At the beginning of the 1900s, it was recognized that Russians have an average intestinal length 57 cm longer than those of people from Poland. On account of this difference, Russians will obtain more calories in comparison to Polish people who consume the same amount of food.

The amount of enzymes secreted in every person also differs according to both genetic differences, and age. For example, while a glass of milk is a source of high energy to some – particularly children – it is not the same for others. Most adult bodies do not secrete the enzyme of lactase, which breaks down the lactose sugars found in milk.

People also have different types of bacteria colonies. Predominantly, two bacteria colonies (bacteroidete and firmicute) are found in human intestines. Research has indicated that there are more intense populations of firmicute in the intestines of obese people. Accordingly, having more than the necessary amount of bacteria in the body increases food digestion and thus causes the body to absorb more food. If these foods supply more energy than the body needs, they are stored as fat.

Some microorganisms are only seen in some people. For example, since Japanese people often consume algae, some microorganisms in their intestines are equipped with the genetic information to code the enzymes responsible for breaking down and digesting algae. This is an adaptive trait humans have: if our intestines stop being suitable for environments for such bacteria to breakdown fibrous foods, our calorie intake will be low, because of the fact that hard nutrients, such as celery or carrots, will not be digested properly.

In recent years, it has been explicitly shown that how food is prepared alters the number of calories the human body can extract from it. Therefore, as the human body digests processed foods rather easily, they provide much energy with little effort from the digestive system. Processed foods also cause the diminishing of the intestinal microorganisms which digest fibrous foods.

On the other hand, as the body extracts more vitamins and nutrients from vegetables, nuts, and whole grains, these all help to maintain the number of beneficial bacteria in our intestines. Those who wish to follow a healthy diet and lessen their caloric intake from nutrients should not eat processed, fried, and well-done foods. Instead, they should eat raw or boiled foods which contain bran and fibers.

As shown, a healthy diet, does not just depend on the type of food, but how that food is cooked, whether it was pre-processed or not, and whether it is swallowed after being chewed well or not. Our health further depends on the diversity and balance of our intestinal microorganisms and flora. It should be noted that without taking into consideration these factors affecting our caloric intake, the benefit of exercise and sports will also be limited.