In the sphere of health and fitness, the word “metabolism” comes up often. But what’s the big deal with metabolism and why does everyone link metabolism to weight management? What is it?
Let’s start with the most basic question, what is metabolism anyway? Metabolism is the body’s process in which it uses energy for growth, tissue-building, maintaining body temperature as well as to sustain the vital functions of the brain, heart, lungs, and other organs.
Basal metabolic rate (BMR) is minimum energy expenditure to stay alive. About 50 to 70 percent of energy expenditure in a sedentary person is BMR. It is calculated in a clinical or /lab setting, as it requires stringent conditions such as: the person should be awake and resting, fasting for 12-18 hours (post absorptive state), in a reclined position, and in neutral temperature and pressure and humidity. However, the second type of metabolic readings is resting metabolic rate (RMR) and is measured under less constrained conditions; usually measured after waking up in the morning.
Both BMR and RMR are can be estimated by through equations (with the use of height, weight, age and sex) or measured through gas analysis (O2 and CO2). Both terms can be used interchangeably; however, BMR provides a more accurate reading of your metabolic rate than RMR.
Factors influencing metabolism:
Multiple factors modulate the metabolic rate of person’s body; here are some of the major factors:
Age: Your metabolic rate slows down with age. The loss of lean body mass and increases in fat is responsible for age related decrease in metabolic rate.
Gender: Men generally have higher BMR than women. In men, the male hormone testosterone increases BMR as it is related to increase in lean body mass.
Body Surface Area: Higher the surface area, greater the BMR. Infants have large surface area, therefore causing them to have higher BMR.
Temperature: People living in a warmer climate tend to have lower metabolic rates than those in a colder climate like the Eskimos.
Barometric Pressure: High altitudes and low oxygen tension mean a fall in BMR.
Physical Activity: A great increase in BMR occurs with intense exercise. Short bursts of muscle contraction or HIIT can increase BMR to a great expense.
Fat Mass and Lean Body mass: The presence of brown fat has an effect on increased thermogenesis and results in higher metabolic rate which is seen in neonates. In obese people, the hormone leptin can cause a higher metabolic rate. Lean Body Mass (LBM) increases metabolism as it burns more ATP/energy than fat mass.
Sleep: During sleep, BMR decreases to 10-15 percent.
Nutritional Factors: Fasting, starvation and malnutrition reduce BMR.
Specific Dynamic Action (SDA) of Protein: A high protein meal causes an increase in metabolism to up to 30 percent above normal and can last for 3 to 12 hours.
Pregnancy: After your second trimester, there is an increase in BMR as fetal energy requirement grows.
Hormones: Growth hormone, thyroid hormone, male sex hormone, and leptin all have an effect on BMR.
Some pathological conditions also have a significant effect on BMR:
-Higher BMR is seen in hyperthyroidism, thyrotoxicosis, diabetes insipidus, leukemia and polycythemia. Conditions such as hypothyroidism and Addison’s disease cause a fall in BMR.
Fever: The rise in body temperature raises metabolic rate.
What can you do raise the metabolic rate?
Sleep to least 7-9 hours
Increase your protein intake to match your body’s needs
Stay physically active
Focus on short burst training and strength training
Do not fall for fad diets
See your doctor to find if any pathological condition is present.
Guyton textbook of medical Physiology 12th edition
Textbook-Principles of Physiology By Debasis Pramanik M.D.
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