BMI introduction

Dangers of being overweight Being

Being overweight raises the chances of developing a number of serious diseases and health conditions. Below is a list of these risks according to the Centers for Disease Control and Prevention (CDC)\

• High blood pressure

• High levels of LDL cholesterol — which is usually regarded as bad cholesterol — low levels of HDL cholesterol – which is usually regarded as good cholesterol when at lower levels – and higher triglycerides

• Type II diabetes

• Coronary heart disease

• Stroke • Gallbladder disease

• Osteoarthritis – which is joint disease resulting from breakdown of cartilage in the joint

• Sleep apnea and breathing problems

• Certain cancers (endometrial, breast, colon, kidney, gallbladder, liver)

• Low quality of life

• Mental illness (clinical depression, anxiety, etc.)

• Body pain and difficulty completing certain physical tasks

• Generally, an increased risk of death compared to those with normal BMI

As can be seen in the long list above, being overweight can result in numerous negative health results, some of which can lead to death. In general, it is best practice to keep BMI as low as 25 kg/m2 — but a person should ideally consult a physician at some point in order assess whether or not changes are needed in order to be more healthy.

Associated Risks of Being Underweight

Being underweight carries its own associated risks, as outlined below:

• Malnutrition, vitamin deficiencies, anemia (decreased capacity to transport red blood cells)

• Osteoporosis, a disease that weakens bones and raises the risk of fracture

• Decreased immune function

• Growth and developmental disruptions, particularly in children and adolescents

• Potential reproductive complications for women as a result of hormone disruptions that can affect the menstrual cycle. Women who are underweight also have an increased risk of miscarriage in the first trimester.

• Potential complications after surgery

• In many cases, a higher risk of death compared to people with a healthy BMI

In some cases, being underweight can be a sign of some underlying condition or disease, such as anorexia nervosa, which has a set of different risks. Talk to your doctor if you believe that you or someone you know may be underweight, especially if the reasoning for being underweight does not appear to be clear..

Limitations of BMI

Although BMI is a commonly used and useful estimate of healthy body weight, it does have limitations. BMI is an estimate and cannot consider body composition. BMI should be considered in conjunction with other measurements instead of being the only measure of a person’s healthy body weight, given the wide range of body types and distribution of muscle, bone mass, and fat.

In adults:

BMI is not a perfect measurement of body fat; it is a measurement of body weight excess – not a measurement of body fat excess. In addition to body weight, BMI is influenced by age, sex, ethnicity, amount of muscle, amount of body fat, activity level, and other factors. An older person at a healthy weight, who is inactive on a daily basis, has considerable amounts of body fat – even if weight is not high. In this scenario, the person is “unhealthy,” while a younger person, with appreciably higher muscle composition, reaches a healthy weight with the same BMI and age. Athletes, especially bodybuilders, are another example of BMI reporting overweight even when they are at a healthy weight for body composition (muscle is heavier than fat). The CDC concludes:

• Older adults will generally have more body fat than younger adults at the same BMI

• Woman will generally have more body fat than male with the same BMI

• Muscular individuals and athletes who are highly trained may have a higher BMI because of muscle mass, compared to body fat.

In children and adolescents:

The factors that affect BMI effectiveness in adults also can apply to children and adolescents. Children’s height, along with puberty, can also impact BMI and body fat. BMI is usually a better indicator of excess body fat for obese children than for overweight children since BMI can either indicate increased fat mass or fat-free mass (e.g., water, organs, muscle, etc.) and presents as the same BMI. For thin children, the BMI difference from their peers may also be due to fat-free mass.

Ultimately, BMI is reasonably accurate as an indicator of body fat in 90-95% of the general population and can be appropriately combined with others measures to assist in determining an individual’s healthy body weight.

BMI formula

Below are the equations used for calculating BMI in the International System of Units (SI) and the US customary system (USC) using a 5’10”, 160-pound individual as an example: