Last Updated December 20th, 2021
BMI & BMR
The energy requirements of a human body are estimated based on multiple parameters that are dependent on the height, weight and age of a person. In many scenarios, these assessments are also needed to determine the needs of the undernourished sections of the population who are deprived of the basic nutrition.
Both the body mass index (BMI) and basal metabolic rate (BMR) are used as standards in these aspects but they are two different parameters. The BMI is dependent on the height and weight of an individual that assesses the overall body composition. On the other hand, BMR is the number of calories that a person burns when at a state of rest.
Even though the two are independently calculated, the BMI value affects the BMR of a person. In fact, the higher the body composition as indicated by the BMI, the higher is the value of the BMR.
What is the difference between BMI and BMR?
BMI is often linked with obesity and a higher value also increases the risk of certain diseases.
But BMI does not distinguish between body fat and lean body mass and does not take into account the physical location of body fat. So those with higher than average muscle mass can also have a high value of BMI even if they are not obese. The calculation of BMR is more complex than BMI and involves an individual’s height, weight, age and gender.
BMR is the amount of energy that is expended in activities like breathing, keeping the heart beating, blood circulating, digesting food and delivering their nutrients to cells, without doing any other external work.
In many cases, the Total Daily Energy Expenditures (TDEE) is calculated for individuals where an activity factor is added to the BMR value. These values are important for people who are looking to achieve specific fitness goals or aiming to reduce weight.
BMI calculation and importance
BMI is calculated based on a person’s weight and height in order to determine whether he or she is underweight, normal weight, overweight or obese. The method does not measure body fat directly but it correlates with other techniques for measurements of body fat.
To calculate BMI, the person’s weight in kilograms is by height in meters squared. In case one is using the English system, then the pounds should be divided by inches squared and the result has to be multiplied by 703. The values obtained to determine the state of a person.
While the values between 18.5 and 25 are considered normal, a person with a BMI between 25 and 30 is considered overweight and a person with a BMI over 30 is considered obese. While BMI is not accurate for those who are pregnant or have a high muscle mass, a high value can be linked with certain diseases related to obesity. Some of these ailments are listed below.
- Liver disease
- Several forms of cancer
- High blood pressure (hypertension)
- High cholesterol and related cardiac ailments
- Sleep apnoea.
- Gastroesophageal reflux (GERD)
Many individuals who had a high BMI reportedly felt better, both physically and psychologically once they reduced their weight by some kilograms. At the same time, BMI is not an indicator of any particular disease or a psychological condition.
There are various factors including food and lifestyle choices that influence health and there are many individuals who are disease-free even with a high BMI. Some studies have also found that even though people with a slightly higher BMI run the risk of a few diseases, they tend to live longer than those with lower values.
It is being stated by health experts that BMI alone is not to be identified with good health or the risk of cardiovascular health, blood sugar or blood pressure. Even though it is a good starting point, BMI has to be taken into consideration with other factors.
The reduction in physical activity due to lifestyle choice has resulted in obesity becoming a vital health issue. Since most people gain weight due to a mismatch between the daily energy consumption and energy expenditure, the minimum daily energy requirement for a person is to be determined.
Apart from body composition, sex and age, it has been recorded that height is an important factor in determining the metabolism rate and taller individuals generally have higher rates. BMR is basically the minimum energy exchange that occurs in the body to support activities like respiration, circulation and secretion.
Even though there are a number of formulas, BMR value is often calculated by the Harris Benedict Equation which is different for men and women. The equations have been revised since their origin, to account for various factors and are stated below.
For Males, BMR= (88.4 + 13.4 x weight in kilograms) + (4.8 x height in centimeters) – (5.68 x age)
For Females, BMR= (447.6 + 9.25 x weight in kilograms) + (3.10 x height in centimeters) – (4.33 x age)
The body composition of a person which involves the proportion of inert body fat and active protoplasmic tissue is an important factor in measuring BMR. Some factors can influence the BMR of a person and they include the following.
- Age: The BMR values will usually decrease with age, which means that people may need to adjust their diet as they get older in order to avoid weight gain.
- Menopause: Those going through this phase, will have their BMR values at a lower level, as they will be burning fewer calories.
- Weight training: High volume of muscles in the body tend to increase the BMR for the long-term. Those undergoing high-intensity interval training will also have higher BMR rates.
The importance of BMR
For those who are trying to lose weight or plan to maintain their current weight, knowing the BMR is an important step. Around 70% of the calories that are consumed by a person is used up for basal metabolic activities. It indicates that calories a person burns when at rest and this data is vital for those who want to stay fit and healthy.
The overall issue of weight loss and healthy weight maintenance is a balance between the number of calories that are gained or lost. The BMR can help in determining how much calories a person needs to burn through the exercise to lose weight. This also helps in preventing the onset of various chronic health problems.
The metabolic activity of the body changes and reduces as a person gets older. So aged people who find it more difficult to lose body fat and overall weight, can be benefitted by the knowledge of BMR.
The BMR values can help you to arrive at the TDEE value for getting a better picture of the calorie consumptions. This value is obtained by multiplying the BMR by a factor that depends on the daily activity of an individual. For those who are trying to lose weight, consuming fewer calories than they are burning is the key.
At the same time, these numbers are a guiding factor in losing weight. A drastic reduction in calories can affect overall health and will also prevent the loss of weight in the long run. The first step that can be taken to enhance weight loss is to cut out unnecessary junk food and snacks from your diet.
The BMR is also affected by the total lean muscle mass in the body as muscles require a lot of energy for maintenance. Any activity that reduces the lean muscle mass of the body will also reduce the BMR of the body.
The process of metabolism
BMR is dependent on metabolism which is a complex process that involves the conversion of food into energy with the help of oxygen. Apart from normal bodily functions, physical activity plays an important role in the consumption of calories. The normal daily activities like walking, cooking or gardening also consume certain amounts of energy and they are termed as non-exercise activity thermogenesis. The metabolism process in the body can be categorised into two different segments mentioned below.
Catabolism –This process involves the breakdown of food into the various macro and micro- nutrients like carbohydrates, proteins and fats which are absorbed by the body to meet the daily needs to grow and repair. This process is also termed as thermogenesis and utilises around 10 percent of the calories that are consumed. A major part of the energy that is generated by catabolism is stored in the high-energy molecule adenosine triphosphate which is found in cells.
Anabolism –The nutrients are used in repairing the body in various ways and that energy expenditure is classified as anabolism. This process builds up larger molecules that are needed by the cells and tissues by chaining smaller ones as need.
Since the process of catabolism generates energy and anabolism uses energy, they should balance each other out in an ideal condition. When the net change is positive, the excess energy is stored in the form of fat molecules. When the net change is negative, the body uses the stored energy to compensate for any energy deficiency. Both these processes are regulated by hormones and there are separate hormones for each category. Cortisol, glucagon, adrenaline and cytokines are some important catabolic hormones. Anabolic hormones include the growth hormone, insulin-like growth factor, insulin, testosterone and oestrogen. All the energy reactions in metabolism are oxidation-reduction reactions that occur in series.
The importance of BMR and BMI in maintaining health
Metabolism is an efficient process that allows the body to maintain a healthy weight in a natural manner. Only in case of some rare disease like Cushing syndrome and thyroid-related problems, the metabolism process is affected, leading to obesity. Since the lack of exercise and a sedentary lifestyle are very common in the present society, obesity has emerged as a major problem.
The BMI of an adult past the growth stage stays in the same range as long as the weight is kept constant. While it is an important indicator of ideal weight, it cannot provide the exact methods one can follow to bring about the necessary change in weight. On the other hand, knowing one’s BMR is helpful for nutritional assessment, weight loss planning and also to care for various medical conditions. As stated earlier, a person with more fat mass will have a higher BMR.
Obesity can be linked with a wide variety of diseases including type2 Diabetes which is widespread. With the correct values of BMI and BMR, preventive measures can be taken in order to reduce the risks of diabetes. The knowledge about BMR is also essential to prevent age-related diseases that affect a large percentage of the aging population.
If old age is coupled with ill health, then the nutritional intake can get adversely affected. This can be combined with metabolic disturbances associated with illness or disability which deplete the energy stores of the body. Hence BMR is extremely important to maintain good health at an advanced age. The details about the energy expenditure process in critically ill patients are still not known and more research is needed in this field.
The importance of a right diet based on BMR
While BMR can help you to mould your diet for the best results, restricting the calorie intake can also bring about some adverse effects as listed below.
- Eating fewer calories to lose weight can result in nutrient deficiencies and chronic fatigue in the body. A restricted diet can also reduce the intake of protein, calcium, iron, vitamins and other nutrients resulting in various complications.
- Cutting down on calories can lower the metabolism rate and prevent weight loss. It can also lead to a loss of muscle mass if a proper exercise regimen is not followed.
- Extreme reductions in calorie intake can also reduce fertility, especially in women. Insufficient calories can affect the levels of oestrogen and luteinizing hormone (LH).
- Since lower calories can affect the levels of oestrogen and testosterone, two hormones that impact bone health, it can also result in loss of bone mass.
- An improper diet can weaken the immune system and make an individual more susceptible to infections and illnesses.
When planning to use the BMR data for weight loss, it is important to plan effectively and be patient to let the right diet take its course.
Both BMI and BMR are important to keep track of the weight and overall health of a person. They are also effective to help you achieve your fitness goals and build more muscle mass.
Since metabolic activity is influenced by many factors it is best to take help of a professional to help you in planning the right diet. This is more important if you have any chronic problems or under medication. Whatever be the BMI and BMR of a person, a healthy diet and a daily dose of exercise is always the right step towards achieving good health.
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