Like the word diet, the word calorie gets a bad rap, especially when it comes to losing weight. Let’s take a little journey so we can better understand what calories are and how they work in the human body.
1. What is a calorie?
A calorie is a unit of food energy. In nutrition terms, the word calorie is used instead of the more precise scientific term "kilocalorie" which represents the amount of energy required to raise the temperature of a liter of water one degree centigrade at sea level.
2. What do calories do?
Human beings (and animals) need energy to survive and they require energy from food. Our food has three main components: protein, carbohydrates, and fats. They are digested in the intestine, then broken down into their basic units: proteins into amino acids, carbohydrates into sugars, and fats into fatty acids. The body uses these basic units to build substances it needs for growth, maintenance, and activity.
3. What is BMR?
BMR stands for Basal Metabolic Rate. BMR is basically the amount of energy your body needs to maintain normal body function. This includes the function of vital organs like the heart, lungs, brain and nervous system, liver, kidneys, sex organs, muscles, and skin, and accounts for about 60-70% of calories burned in a day. The amount of energy required by these processes must be met before any of those calories can be used for food digestion and physical activity.
4. What can affect one’s BMR?
One’s BMR can be influenced by a combination of genetic and environmental factors: genetics, age, gender, weight, body surface area, body fat percentage, body temperature and health, external temperature, glands, diet, and exercise. Here a few explanations.
Genetics:
Some people are born with faster BMR, some with slower.
Age:
BMR reduces with age. Because of the increase in cellular activity (cells undergoing division), BMR is highest during the growth spurts that take place during childhood, adolescence, and pregnancy. BMR peaks at age twenty for males and females, then decreases by about 2% per decade throughout life. This decline during adulthood may result partly from a decrease in physical activity and the subsequent loss of muscle tissue.
Gender:
Due to a greater percentage of muscle mass (lean tissue) and a lower body fat percentage, men generally have a higher BMR than women.
Body fat percentage:
The lower the body fat percentage, the higher the BMR. Since the male body has a lower body fat percentage–they generally have a 10-15% higher BMR than women.
Article comments
1 - Bob Lloyd
Although the intention of the article is very good, there are some glaring factual mistakes about the human body. I hope you don't mind me correcting them here.
[Protein is the "cellular building block" and is a main component of bones, muscles, organs, glands, cartilage, skin, and blood.]
This is misleading. A protein is just a string of amino acids, it's a biological chemical. They are found throughout the body and are no more a main component than water is. They are ubiquitous and provide a very wide range of functions but in essence, they are just chemicals. In the case of bone, the main component is not protein, but calcium phosphate, an inorganic chemical.
[Fats aid in heart and brain health, prevention of certain cancers, and help reduce other ailments like depression, inflammation, and blood pressure.]
Fats is a common term for lipids, a class of biochemical which includes steroid (as in hormones), phospholipids (as in cell wall proteins), many vitamins, and even polyketides.
Saying they help in heart and brain health is meaningless but saying they aid in prevention of certain cancers and reduce depression symptoms is positively misleading and shows a lack of understanding of the medical details. The implication is that you need them to stave off depression - which is nonsense. You need them to stay alive.
The fact is that foodstuffs are digested, that fats, proteins, and carbohydrates, are metabolised into simpler chemicals which are then used to synthesise a wide range of complex biological molecules. These biological molecules are ubiquitous, all around the body, and they can't be associated with specific functions in the way you describe.
Proteins for example include hormones (chemical messengers), structural components (such as collagen), enzymes (such as pepsin), carriers (such as haemoglobin), and so on. Proteins perform a diverse range of functions throughout the whole body.
The same could be said of the metabolic products of fats and carbohydrates. It's simply incorrect to say that "Not all calories are created equal". Calorie is a measure of energy and the body doesn't care what the source of the energy is. Once it's metabolised and the energy is absorbed into the bonds of ATP (Adenosine Triphosphate, the main energy storage and transport mechanism of the body), all calories are identical.
I appreciate your intention to get people to be sensible about this stuff, but it is really important to get the biological details right. The whole detox industry seems intent on spreading confusion and misunderstanding so it's important that people don't get the wrong idea about things like carbohydrates, fats and proteins, and their role in human biology.
2 - Christine
Bob: thanks for your insight and I was trying to speak so that the average person could understand. Will recheck later.