Relative to food and the body, calories are units of energy that allow the body to function. Food provides this energy, some of which the body stores and some of which it uses. As the body breaks down food, it releases calories as energy. Max Wishnofsky first propagated the concept that there are approximately 3,500 calories in a pound (lb) of body fat.
Simply put, to lose 1 pound of body fat per week, people will need a deficit of around 500 calories per day. They can achieve this by consuming approximately 500 fewer calories than they currently are, burning an additional 500 calories per day with exercise, or a combination of the two.
If the body consumes too many calories or burns too little, weight gain occurs. This is because the body stores calories that it does not use as body fat. Organs including the brain, heart, lungs, liver, and kidneys account for approximately 80% of total daily energy use.
Recent research calls into question this rule, concluding that it overestimates someone’s weight loss potential. The rule does not account for dynamic changes in metabolism, hunger, and satiety levels as weight loss occurs.
The National Institutes of Health have developed a new, more precise rule of thumb: every 10 calorie decrease per day leads to a final loss of 1 pound. Only time will tell how long it takes to lose weight, so patience and consistency are key.
How fat works
Body fat, or adipose tissue, consists of adipocytes. These are fat cells and are produced together with other types of cells and proteins. Fat cells contain lipids, including cholesterol and triglycerides.
Fat tissue stores energy for the body to use and protects organs. It also releases hormones that control many functions in the body, such as insulin sensitivity and appetite.
People with more body fat can experience something called leptin resistance, in which the body is less sensitive to the satiety hormone leptin. This, in turn, increases hunger and food intake, making it difficult to maintain weight over time.
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There are two types of adipose tissue: white and brown. Brown adipose tissue is more metabolically active. Burns more calories and helps control weight, insulin sensitivity, and overall health to a greater extent than white adipose tissue. If people have excess body fat, it is more common that their white adipose tissue has expanded.
Having too much body fat can cause obesity and cause many health problems, such as diabetes, high blood pressure, and heart disease. Having too little body fat can also be harmful and lead to health problems like malnutrition and fertility problems.
How do calories work?
Research estimates that muscle burns calories at a rate of 10 to 15 calories per kilogram (kcal / kg) per day. This equates to 4.5–7 kcal / lb per day. Muscles account for approximately 20% of total energy expenditure each day. For people with 20% body fat, body fat represents 5% of energy expenditure.
So people with more muscle tissue have a higher metabolic rate. This means that they burn more calories and can maintain their body weight more easily.
How do we calculate calories?
Calories in food are not exactly the same amount inside the body as they are outside the body.That said, scientists measure the amount of caloric energy that food contains by using a device called a bomb calorimeter. By burning food in this device, scientists can measure the heat released to find out the number of calories in the food.
This provides a figure for the total potential energy of food. However, this is not a true reflection of how the body will use energy from food. The body cannot always use all the calories that people consume.
Calorie losses can occur due to:
- To pee.
- Incomplete digestion of food.
- Have an ineffective metabolism.
How people burn calories will depend on their metabolism, digestion, and general health and fitness levels.
A calorimetry machine can show how many calories people burn when they rest. This is called your basal metabolic rate. The machine measures carbon dioxide, which is the waste product of food that the body burns for energy. Other accurate methods of estimating calorie expenditure use air or water displacement technology.
With these tools, people can calculate a precise number of calories burned during rest, activity, or exercise. It is important to recheck this number every 3–6 months to understand how body composition and calorie needs change over time.
People can use calorie counting tools and fitness trackers to get a rough idea of how many calories they are consuming and how many they are burning. However, this will not always be completely accurate.
The body needs a certain amount of healthy fat to function properly. Research suggests that while there is no single macronutrient dietary plan that works for everyone due to individual needs, most health experts recommend the following amounts of carbohydrates, proteins, and fats for a balanced diet:
- Healthy fats: 20–35% of calories.
- Protein: 15-20% of calories.
- Complex carbohydrates: the remaining percentage of calories.