Beyond the Bathroom Scale: Healthy Body Weight

Figuring out a person's perfect body weight is surprisingly difficult
December 21, 2020 Updated: December 21, 2020

Discussing weight and figuring out what healthy body weight is has been a popular topic for centuries. For much of history, extra weight was considered an indication of good health, wealth, and success, although that has changed over time.

As the years have passed, people have developed complex ways of understanding and measuring healthy body weight.

Body Weight Statistics

Statistical breakthroughs had a major impact on our understanding of healthy weight. In 1846, Sir Jonathan Hutchinson, a British surgeon, published a table of “average” weights for each inch of height from 61 through 72 inches, using information gathered from 2,650 30-year-old men. This table was utilized by life insurance companies as a guide to evaluate applicants.

The introduction of a penny scale, around 1885, in Germany and the United States, then permitted the public to measure body weight to the nearest pound. These scales were a public draw, costing those that wished to know their weight a penny.

Body weight statistics evolved further in the beginning of the 20th century, as the purchase of insurance policies grew in popularity.

Healthy weight became an important factor for insurance companies, as medical professionals had established a relationship between being underweight and death from tuberculosis and pneumonia and, conversely, being overweight and death from heart-related conditions.

The Metropolitan Life Insurance Co. was able to develop standard weight or “height to weight” charts. Those tables, using information gathered from middle-aged males, are the basis for the current definition for underweight, normal, overweight, and obese individuals.

Many people, when thinking of body weight, may point to body mass index or BMI. Nutrition and dietetics students and professionals will likely recognize the name of Belgian astronomer and mathematician Adolphe Quetelet (1796–1874), the inventor of the concept.

Quetelet applied probability calculus to the human body, looking for “norms.” In 1835, he published “A Treatise on Man and the Development of His Aptitudes,” with the conclusion that healthy weight could be mathematically calculated. Known then as the Quetelet Index, and now as BMI, this was the first table, still in use, that indicated “average weight” at ages 20 through 60.

The Current Standard

Body mass index (BMI) is a person’s weight in kilograms divided by the square of height in meters. A higher BMI can indicate elevated body fatness, and a lower BMI can indicate decreased body fatness. To calculate your BMI, you can use an online BMI calculator or a height and weight chart.

In general, health care professionals use the following guide: if your BMI is 18.5 to 24.9, it falls within the normal or healthy weight range. If your BMI is 25.0 to 29.9, it falls within the overweight range. If your BMI is 30.0 or higher, it falls within the obese range.

But there are shortfalls to the system.

BMI calculations don’t take age or gender into consideration, or provide information on the location or amount of body fat, important factors for predicting certain health conditions. It’s possible to be “overweight” according to BMI, but have healthful levels of fat. For extremely muscular people, such as athletes and bodybuilders, height and weight measurements alone may not accurately indicate health, because muscle weighs more than fat.

A healthy, muscular person may have a BMI in a very high range. Meanwhile, a frail, inactive person with a low BMI may have a dangerously low level of muscle.

BMI alone can’t show whether a person’s weight is healthful, but using it in combination with other indicators can provide a more complete picture. One of those indicators is waist circumference.

Waist Circumference

Waist circumference can tell us if our weight is being gathered in muscle or fat. And where we wear our fat is important also. Generally, abdominal fat is considered more dangerous than hip fat. People with abdominal fat are at greater risk of insulin resistance, diabetes, heart disease, and stroke.

To correctly measure waist circumference, stand and place a tape measure around your middle, just above your hip bones. Make sure the tape is horizontal around and keep it snug around the waist but don’t compress the skin. Measure your waist just after you breathe out. A man whose waist circumference is more than 40 inches or a non-pregnant woman whose waist circumference is more than 35 inches is considered to be “elevated” in weight.

Other Measurement Systems

There are many technologies that have developed around estimating and tracking a healthy body weight, from smart phone apps to total immersion pods. Figuring out the perfect body weight turns out to be surprisingly personal. It depends on many factors and can be difficult to ascertain. That hasn’t stopped people from trying though.

Skinfold Thickness

One more familiar and longstanding method is to measure skinfold thickness. People who have quickly fluctuating weight may do this themselves, pinching an area of fat accumulation and noting how much bigger or smaller it is.

But there are more scientific ways to do this using a special caliper to measure the thickness to “pinch an inch” of skin and the fat beneath it. This is done in specific areas of the body: the trunk, the thighs, front and back of the upper arm, and under the shoulder blade. Equations are used to predict body fat percentage based on these measurements. This is a convenient, portable, and inexpensive method used in schools and the military, but is not unerringly accurate.

Bioelectric Impedance (BIA)

BIA equipment sends a small, safe electric current through the body, similar to an EKG, measuring the resistance. The current gets more resistance passing through body fat than it does passing through lean body mass and water. Equations are used to estimate body fat percentage and fat-free mass. The ratio of body water to fat may change during illness, dehydration or weight loss, which can decrease the accuracy of this method.

Underwater Weighing (Densitometry)

This method involves putting on a swimsuit and being completely submerged in water. Individuals are weighed in air and then while submerged in a tank.  Formulas to estimate body volume, body density, and body fat percentage are then used. Fat is more buoyant (less dense) than water, so someone with high body fat will have a lower body density than someone with low body fat. This method is time-consuming and generally not a good option for children or older adults.

The BodPod or Air-Displacement Plethysmography

This method uses a similar principle to underwater weighing but can be done in the air instead of in water. Individuals sit in a small chamber such as in the “Bod Pod.” The machine estimates body volume based on air pressure differences between the empty chamber and the occupied chamber. This expensive method is relatively quick and comfortable and a good choice for children and older adults, and other individuals who wouldn’t want to be submerged in water.

Dual Energy X-ray Absorptiometry (DEXA)

X-ray beams pass through different body tissues at different rates. DEXA uses two low-level X-ray beams to develop estimates of fat-free mass, fat mass, and bone mineral density. DEXA is becoming more popular for estimating healthy body weight, with the added benefit of estimating bone density. Of course, X-rays aren’t a risk free way of evaluating the body given the radiation risk.

Feeling Good About the Skin You’re In

Cultural values and norms affect how we think about a healthy body weight. Over the years, many cultures have valued “chubbiness” or “curves” rather than thinness. Social ideals change with time. In the United States and Europe, “thin” continues to be “in.”

But what is a healthy body weight? A healthy weight is a weight that lowers your risk for health problems. With the immense variety of different body types out there, it is impossible to have a one-size-fits-all method of saying a certain weight is healthy.

Being very thin can sometimes have little to do with good health, just as having a “few extra pounds” may not be an indication of poor health status.

And while it can be fashionable to be “on a diet,” what you really need to do is find a healthy way of eating you will stick to indefinitely. If you want to lose weight, rather than go on a diet, change your food philosophy. Become mindful about eating and focus on vegetables, fruit, and whole grains.

Plan to make changes slowly. Try to make physical activity a regular part of your day, and plan to do something nice for yourself on a regular basis. A healthy lifestyle, which includes a healthy weight, isn’t just about the numbers on the bathroom scale.

Dr. Nancy Berkoff is a registered dietitian, food technologist, and culinary professional. She divides her time between health care and culinary consulting, food writing, and healthy living.