It is a frequent complaint from Dieter: “Ugh, my metabolism is so slow that I will never lose weight.”
When people talk about a fast or slow metabolism, they really get how many calories their body burns during their day. The idea is that someone with a slow metabolism doesn’t use the same amount of energy to do the same job as someone with a fast metabolism.
But does the rate of metabolism really vary greatly from person to person? I am a nutritionist focused on the biological, environmental, and socio-economic factors that affect body composition.
– This question is tougher than it may seem – and regardless of the current rate of your metabolism, there are things that will put it in a lower or higher gear.
Your body’s energy needs
Metabolism is a biological term that refers to all chemical reactions required to sustain life in an organism. Your metabolism has three main functions: converting food into energy; Breaking down food into its building blocks for protein, lipid, nucleic acid and some carbohydrates; and elimination of nitrogen waste.
If you are agonized about the speed of your metabolism, your focus is likely to be on how much energy you get from the foods you eat and how much your body is consuming. The energy value of a food is measured in calories.
Your calorie needs can be divided into two categories.
The basal metabolic rate is the minimum amount of calories that is required for the basic functions at rest. Resting energy expenditure is the amount of calories you burn off while resting or sleeping – about 60 to 65 percent of your total energy expenditure.
It doesn’t take into account the calories you need to power everything else – exercise or energy expenditure (25 to 30 percent), thinking, and even digesting food (5 to 10 percent). Your total energy consumption therefore combines both: your resting energy consumption plus your energy consumption for other activities.
Find a number
The estimated daily calorie requirement of an adult woman weighing 57 kg is between 1,600 and 2,400 calories per day. For a 70kg man, the daily calorie requirement can be anywhere from 2,000 to 3,000 calories per day. That’s roughly 13 calories per pound of body weight.
In contrast, infants burn about 50 calories per pound of weight per day. This requirement continuously decreases with the age of the child. So infants have the highest metabolism of all. This additional calorie requirement is necessary for growth.
So if two women of the same weight can have caloric needs that vary by up to 30 percent, does that mean the woman whose body is consuming more calories has a faster metabolism than the woman whose body is consuming fewer calories? Not necessarily. A woman may spend more of her day being physically active and therefore need more energy to power her sidewalk and kickboxing class after work, for example.
Beyond these broad guideline areas, there are many ways in which you can estimate resting and total energy expenditure if you want to determine your body’s specific caloric needs.
A common and simple method is to use predictive formulas such as Mifflin-St. Jeor or Harris-Benedict equations based on your age, height, weight, and gender to find out how much energy your body needs to be alive. To calculate the total energy consumption you also need to add the activity factor.
Indirect calorimetry is another way to estimate metabolic rate. Energy consumption is calculated by measuring the amount of oxygen consumed and the amount of carbon dioxide released by the body.
Your body relies on oxygen to do all of its metabolic tasks. For every liter of oxygen you use, you are using approximately 4.82 calories of energy from glycogen or fat. Indirect airway calorimetry is usually done in a doctor’s office, although small, portable, and less expensive devices are increasingly being launched.
Factors that affect metabolism
Metabolic rate and calorie needs vary from person to person, depending on factors such as genetics, gender, age, body composition, and the amount of exercise you do.
The state of health and certain diseases can also affect the metabolism. For example, one regulator of metabolism is the thyroid, which is located at the front of the throat, just below the Adam’s apple. The more thyroxine a person’s thyroid produces, the higher that person’s basal metabolic rate.
Fever can also affect a person’s basal metabolic rate. For every 0.9 degrees Fahrenheit (0.5 ° C) increase in a person’s internal body temperature, their basal metabolic rate increases by approximately 7 percent.
Other diseases that affect the basal metabolic rate can include muscle wasting (atrophy), persistent hunger, low oxygen levels in the body (hypoxia), muscle disorders, depression and diabetes.
Another important factor is body composition. For example, an overweight woman with a body composition of 40 percent body fat and 34 kg of muscle burns fewer calories while resting than a woman with 30 percent body fat and 50 kg of muscle mass. Muscle tissue is more metabolically active in the body than fat tissue.
This is also the reason why the basal metabolic rate decreases with age. As people get older, they usually lose muscle mass and gain fat tissue – which translates into a decrease in basal metabolic rate of about 1 to 2 percent per decade.
If you really want to give your metabolism a boost, the easiest way is to increase your muscle mass and activity level. As you increase muscle mass, you also increase the basic number of calories needed to maintain those muscles. Instead of complaining about a slow metabolism, you can try to at least make it a little faster.
Terezie Tolar-Peterson, Associate Professor of Food Science, Nutrition, and Health Promotion, Mississippi State University.
This article is republished by The Conversation under a Creative Commons license. Read the original article.