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.
Some people are born with faster BMR, some with slower.
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.
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.
BMR and Muscle Mass:
Muscle tissue is metabolically, highly active even at rest, whereas fat tissue is not. Thus, lean body mass (LBM) greatly influences a body’s energy requirements and, in conjunction, its nutrient needs. An increase in muscle mass, for both males and females, will elevate BMR.
Starvation and Restrictive Dieting:
Metabolic rate can drop to as low as 20-30% during a period of starvation and restrictive low-calorie dieting. This drop is due to the body’s effort to conserve energy (and its eventual loss of lean tissue) by slowing its BMR. This slowing process is a natural protective mechanism that conserves fat stores when a food shortage occurs. Because of this, consumption of fewer calories than required to sustain BMR will be counterproductive, and can actually cause body fat levels to increase.
5. What impact does exercise have on BMR?
While we can’t change our genetics, age, gender, height or (in most cases) our environment, we can change our body composition. We can decrease our body fat and increase our lean body mass (LBM), which will mean a higher metabolic rate. Changing our body composition is done through proper diet and exercise — two things that will directly impact BMR.
Exercise can increase BMR and, depending on intensity and duration, the metabolic rate may remain elevated for several hours afterward. During sustained, large-muscle exercises like running and swimming, people can generate metabolic rates that are ten times higher than their resting values. Exercise will also increase your muscle mass, which will then increase your BMR.
This is why many top athletes can consume high amounts of calories and still maintain low body fat. The value of exercise cannot be overlooked — it is critical for both short and long-term weight loss; it prevents obesity, poor posture, muscle and bone loss, pre-mature aging, depression, and many other health issues, and it facilitates ultimate fitness levels; physically, mentally, and emotionally.
6. Calculating daily calories. Gender: why men can eat more than women and what women can do about it.
Whether you are interested in health, fitness or weight loss, calories should always be calculated according to your personal BMR, activity level and other variables. While gender is an influential factor for women, it is not necessarily the culprit when it comes to a lower BMR. Instead, a woman’s lower BMR is due to a smaller proportion of muscle mass to fat. That said, females should consume fewer calories than men (childhood, adolescence, pregnancy and athletes excluded). Girls, don’t despair; if you exercise you can eat more. Even though exercise in general increases BMR, strength training is the master to key to the development and protection of lean body mass, which as stated earlier, increases BMR, thus guaranteeing weight loss. However, there is a limit to how much muscle mass females can or want to have on our physique, so we as women have to deal with our limitations when it comes to calorie consumption.
Still, both male's and female’s food consumption should always match their BMR and activity level. If the goal is weight loss or maintenance, neither gender should eat more calories than needed. On the other hand, if we swing in the other direction and don’t eat enough (anything under 1000 calories per day), our predicament is just as grim.
7. Not all calories are created equal.
We get our calories from three main sources, each with a different function and energy potential. In a healthy diet even for weight loss or maintenance, balance of all three nutrients is crucial.
Protein is the "cellular building block" and is a main component of bones, muscles, organs, glands, cartilage, skin, and blood. It also aids in the development, maintenance, and repair of all body tissue and the formation of hormones, enzymes, and other body chemicals. Protein is important for growth and development during childhood, adolescence, and pregnancy.
Carbohydrates are our chief "energy source", providing energy for all bodily functions and muscular exertion. They are also the only source of energy for the brain, nervous system, and red blood cells. Carbohydrates help regulate protein and fat metabolism and are required to break down fats in the liver. They help regulate blood glucose levels, assist in digestion and assimilation of other nutrients, and they provide nutrients for bacteria in the intestinal tract that aid digestion.
Fats supply "necessary nutrients" like essential fatty acids from mono- and polyunsaturated fats. They aid in growth, maintenance of healthy skin, vitamin absorption, and regulation of bodily functions. Although fats are not the chief energy source like carbohydrates, they do provide energy and are considered the most concentrated fuel source. Fats aid in heart and brain health, prevention of certain cancers, and help reduce other ailments like depression, inflammation, and blood pressure.
8. Each nutrient has a particular energy potential.
The caloric energy of a particular food depends on how much protein, carbohydrate, and fat it contains. Most foods contain mixtures of these three nutrients and are classified by which is most predominant. A food rich in protein, like beef, actually contains a lot of fat, while a carbohydrate-rich food like grain contains small traces of both fat and protein.
Caloric yield by nutrient type:
• one gram of protein: four calories
• one gram of carbohydrates: four calories
• one gram of fat: nine calories
Even though alcohol is not a nutrient it does contain calories: one gram of alcohol equals seven calories.
9. Weight control is a question of energy balance:
Energy in = Energy expended = WEIGHT STABLE
Energy in > Energy expended = WEIGHT GAIN
Energy in < Energy expended = WEIGHT LOSS
Although calories are necessary to sustain life and each nutrient has a particular function for health and well being, an excess of any of these will be converted by the liver and stored as fat. Even good calories, when consumed in large amounts, can end up doing harm.
Like many well-designed machines, the body stores energy for future use. Its primary means of storage is fat, or adipose tissue, which lies beneath the skin and surrounds the organs. You can think of fat and its caloric potential as a gas tank for the body. But, unlike a gas tank, the body’s capacity to accumulate an energy reserve is almost limitless. Calories consumed in excess of the body’s needs are stored as fat (in your fat cells — around your internal organs and visible places like your hips, butt, thighs, etc.).
10. Good news!
It sounds simple, but in reality it is somewhat complex. Calculating the correct amount of calories (energy) to consume each day for both men and women, then trying to figure out the proper nutrient ratio can be like trying to do your first science project when you were ten. Considering the facts and the critical role calories play in life, wellness, activity, health, fitness as well as weight loss, at the end of the day or in the context of this subject matter, the beginning of the day, we can conclude that calories are our friends, providing we are consuming pure and wholesome foods.