What is BMR or Basal Metabolic Rate
The basal metabolic rate is the amount of energy that the human body uses when it is completely at rest. This is the amount of energy your body needs to perform basic functions. These include breathing, circulating blood, regulating temperature, and supporting brain and nerve activity.
The organs that use the most energy at rest are the brain, the central nervous system & the liver. What’s interesting is that, throughout the day, more energy is consumed by the regulation of fluid volumes and ion levels than in the actual mechanical work of contracting muscles (e.g., breathing). Active transport moves substances across cell membranes, even when it means going against a concentration gradient (from an area of low concentration to an area of high concentration). This process requires energy. When you consider the entire body, this energy requirement becomes substantial. This also explains why the central nervous system needs so much energy relative to the Basal Metabolic Rate.
When a neural impulse is conducted, a lot of different ions change their location. Afterward, they need to be transported back to their original place.
People typically use more energy than their Basal Metabolic Rate (BMR). This is because they are active and not resting in bed all day.
Walking, running, working, talking, and even digesting are actions that require some extra energy greater than the Basal Metabolic Rate.
To use very little energy, you must be physically and mentally still. This means avoiding muscle use and intense thinking. You should be as relaxed as possible, in a comfortable temperature, and not digesting food. Scientists often measure BMR during sleep to ensure these conditions are met.
As you get older or have less muscle, your BMR usually goes down. But, building more muscle can increase your BMR.
BMR (kcal / day) = 10 * weight (kg) + 6.25 * height (cm) – 5 * age (y) + s (kcal / day), where s is +5 for males and -161 for females.
BMR vs. RMR
When researching Basal Metabolic Rate, you may have also encounter the term RMR. It stands for the Resting Metabolic Rate. Resting Metabolic Rate is similar to BMR. It is a measure of a human body’s energy expenditure at rest without performing any additional activities. However, there is a slight difference. Resting Metabolic Rate also includes the energy used for the digestion of food.
Our body uses some energy for digestion. It transforms food in our gut into usable substances. Food digestion accounts for around 10% percent of your Total Energy Expenditure. Because of that, RMR has a higher value than BMR. We use the modified Harris-Benedict formula, instead of Mifflin St Jeor equation, to calculate Resting Metabolic Rate.
Do you need to eat below your BMR
Eating below your BMR isn’t harmful, but it’s usually not needed to achieve your desired physique. Contrary to popular belief, it won’t harm your metabolism or hinder weight loss. Calorie restriction can cause a small, temporary decrease in metabolic rate. This occurs regardless of whether you eat above or below your BMR. Eating below your BMR isn’t inherently more harmful than eating above it.
Although there’s nothing inherently wrong with eating below your BMR, it requires restricting your calories unnecessarily. This approach is often counterproductive for losing weight and keeping it off.
This kind of “crash dieting” often results in extreme hunger and cravings. It causes lethargy and irritability. Such dieting leads to poor performance in the gym and subsequent overeating and weight gain.
Increasing BMR to lose Weight
The most reliable way to increase your BMR is to increase your muscle mass. This is because muscle is more metabolically active than other types of tissue such as body fat. Thus, the more muscle you have the more calories you burn even at rest.
Factors affecting BMR
The more your body weighs (and the more cells it has), and the more kilocalories it needs. With increasing weight, your Basal Metabolic Rate will rise as well. However, BMR doesn’t depend solely on weight.
•FM – shortcut for fat-mass. As the name suggests, it is the weight of all the fat in our body. Although much lower, fat-mass also has an influence on our Basal Metabolic Rate.
•FFM – standing for fat-free mass. It is the weight of your body without the weight of any fat tissue. If you think about it, it makes sense. Muscles, even at rest, use up a lot more energy than fat. In fact, the main function of fat tissue is to preserve energy in the form of fatty acids. A high ratio of fat-free mass to fat-mass increases BMR.
•Age – your BMR increases with each year as you grow up and as your weight increases. For adults, BMR tends to decrease as they get older. Researchers mainly attribute this to change in body composition over time. As the body ages, the fat-free mass drops. Consequently, the Basal Metabolic Rate becomes lower.
•Sex – men have a statistically higher BMR. The reason is that their fat-free mass is, on average, higher. This is why the creators of this equation made a special adjustment. They added plus 5 kcal/day for men and minus 161 kcal/day for women.
•Genetics – every person is slightly different regarding their BMR. These can be explained by the rate of your metabolism encrypted into your DNA.
•Exercise – How much you exercise impacts your BMR, particularly with strength training. Building muscle increases your FFM (fat-free mass). Be sure not to overdo it when you exercise.
•Body temperature – Your BMR goes up when your body temperature increases. When you have a higher temperature, like during a fever, the chemical processes in your body speed up. This means your body needs more energy, which causes your BMR to increase.
•Temperature of environment – In colder temperatures, your body needs to produce more heat to keep its normal temperature. This process increases your Basal Metabolic Rate (BMR).
•Hormones – Hormones are produced by glands throughout the body. They regulate the functions of organs and tissues. The thyroid gland is particularly important for modifying BMR (Basal Metabolic Rate). The hormones it releases control your metabolism. High hormone levels in the blood increase your BMR, while low levels decrease it.
•Pregnancy – When a woman is pregnant, a fetus (the baby) develops inside her. The fetus has its own metabolism and Basal Metabolic Rate (BMR). The mother provides all the fetus’s nutrition. Therefore, to calculate the total basic calorie needs, the fetus’s BMR must be added to the mother’s BMR.
Research indicates that each pound (0.45kg) of muscle burns 6 to 7 calories daily. Gaining 20 pounds (9 kilos) of muscle could increase your BMR by roughly 120-140 calories per day. This means you could burn almost 1,000 extra calories a week without any extra effort.