How are BMI and BMR different and what do these numbers mean?

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.

• Diabetes
• Arthritis
• 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.

BMR calculation

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 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.

Conclusion

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.

References

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