Weight Loss

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BMI: Body Mass Index

Body mass index is a measure of body fat, though it is not the most ideal method to assess weight and health risks. Learn what BMI actually means and how it can work for you.


Physicians and researchers use BMI to categorize a person's weight. The numerical value offers valuable information about the patient's risk of developing certain health conditions.

BMI is not, however, the ideal way to assess someone's weight - or their health for that matter.

So, what does BMI actually mean and how does it work?

How Does BMI Work?

Body mass index (BMI), less commonly known as the Quetelet index, is a measure of body fat. It is derived using height and weight (mass) and applies to adult men and women.

The equation for BMI is kg/m2, in which kg is a person’s weight in kilograms. The m2 is height in meters squared. In imperial units, the formula is BMI = lbs. x 703/in2.

Adults can use an online BMI calculator, too, for simplicity. The Centers for Disease Control and Prevention (CDC) also offers a BMI calculator for children.

The precision of BMI also mostly depends on obtaining an accurate weight, and natural weight fluctuations occur throughout the day. The number on the scale best reflects body weight in the morning and after using the bathroom. It should also be without heavy clothing including shoes.

Healthy BMI Range

After calculating BMI, it then falls into a weight category. BMI classifications help identify if current weight is considered underweight, normal, overweight, or obese:

Risks Associated with BMI

BMI is an objective and cost-effective screening tool to gauge weight status and potential consequences of an unhealthy weight.

A high BMI and carrying extra weight increase the risk of type 2 diabetes, heart disease, and other health problems. On the other hand, an "underweight" classification may be associated with malnutrition or even help pinpoint an eating disorder.

Especially over the long-term, a low BMI increases the risk of fragile bones, anemia, hair loss, dry skin, and infertility. It can also weaken the immune system, in turn making one more susceptible to viruses, infections, and other health risks. Moreover, a research study found lower BMIs were more at risk of death from respiratory disease and miscarriage in women.

However, BMI is not the best measure for health. Because this measurement only considers scale weight, it becomes erroneous for one with greater lean muscle mass. This often classifies athletes and weight lifters as “obese” due to the large amount of lean muscle tissue.

BMI is also not an ideal gauge in the elderly, who may have lost muscle related to aging and limited mobility.

BMI versus Body Composition
BMI is a general measurement of overall body weight. Body composition, on the other hand, considers certain amounts of fat, muscle, and water. It can also pattern changes in these masses.

Methods to measure body composition include body fat percentage, waist circumference, and waist-to-hip ratio:

• Body fat percentage is the weight of total body fat divided by total body weight. The result helps indicate essential and storage fats.

Essential fat is the amount of fat needed that is essential to survive. Storage fat consists of fat accumulation, some of which protects our internal organs in the chest and abdomen. Other storage fat is excess that increases the risk of chronic disease.

Body fat and its percentage is measured through various methods, including skinfold measurements and a bioelectric impedance analysis. Once determined, it can be analyzed using the American Council on Exercise’s body composition percentage chart.

• Waist circumference measures waist size just above the belly button and below the rib cage. The measurement considers fat distribution in the abdomen and is a stronger predictor of heart disease and diabetes than BMI.

Men and women are advised to keep waist circumference under 40 and 35 inches, respectively.

• A waist-to-hip ratio measurement is the ratio (WHR) of the circumference of the waist to hips. WHR is calculated by measuring the smallest circumference of the waist. It is then by the circumference of the hips at the widest part.

According to the World Health Organization (WHO), the ideal WHR for men is less than 0.9 and 0.85 for women.

Controlling Your BMI

First and foremost, consult with a doctor and/or dietitian to help determine an ideal body weight and disease risk. They can also devise a plan to meet individual needs and preferences.

Ultimately, though, one can control BMI, weight, and health by adopting a healthier lifestyle. This often includes:

• Focusing on whole foods, such as whole grains, fresh produce, lean proteins, legumes, dairy products, and healthy fats.

• Reducing packaged, convenience foods laden in refined flour, sugar, oil, and salt.

• Aiming for at least 150 minutes of aerobic exercise weekly, including brisk walking, jogging, cycling, and swimming.

• Incorporating resistance and strength training at least two to three times each week.

• Ensuring seven to nine hours of sleep nightly.

• Managing stress with positive coping techniques, including with yoga, meditation, and exercise.

• Considering a weight loss meal delivery serving. BistroMD offers healthy meals right to your doorstep along with ongoing support from nutritional experts!

Truly, do not let BMI dictate personal feelings of health. Also assess how clothes are fitting, if waist circumference is changing, and energy levels when losing or maintaining weight!

Written By Sydney Lappe, MS, RDN. Published on November 07, 2012. Updated on April 30, 2019.


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