Body mass index (BMI) is a measurement based on a person’s weight in relation to their height. It is sometimes used to designate being overweight or obese, categories that apply to a majority of Americans including people age 65 and older.

But age-related muscle loss, called sarcopenia, can complicate the meaning of BMI. Geriatrician Colleen Christmas, M.D., with the Johns Hopkins Division of Geriatric Medicine and Gerontology, offers perspective on why BMI may not be the best way to determine obesity among adults who are older and discusses the roles of muscle, fat and weight in the well-being of people age 65-plus.

Is BMI accurate?

BMI is not always a reliable measure of health, especially for adults age 65 and over.

“BMI is shorthand,” Christmas says. “It doesn’t tell the whole story about race, age, fitness and body composition. Does the person with a high BMI have the disease of obesity? Maybe or maybe not. There certainly is some association between BMI and good health, but it’s not a close one.”

She adds that BMI and its categories of underweight, healthy, overweight and obese may be somewhat biased.

“BMI was established for adults of European ancestry, and the numbers don’t always indicate health risk among people of other ethnicities very accurately,” Christmas says.

For example, while BMI charts designate “healthy” as a BMI of 19 to 24, Christmas explains that for adults 65 and older, higher BMI numbers may actually signal better health and higher chances of survival.

“About 60% of older adults have a BMI that would plunk them in the overweight or obesity bucket,” she says. “But not all of these people need to lose weight. It’s more important to consider how a person’s weight affects their quality of life or raises risk for disease.”

Sarcopenia

Another consideration is sarcopenia, the common tendency to lose muscle mass due to aging. Starting as early as a person’s 30s, skeletal muscle weight (mass) begins to shrink (atrophy). By the time the person is in their 70s, they may have only half the muscle weight they did in their 20s.

“Muscle weighs more than fat,” Christmas explains. “A person with a ‘healthy’ BMI who has lost muscle mass and replaced it with fat may not be as healthy as the BMI would indicate.”

Factors thought to contribute to sarcopenia include:

• Increased all-over (systemic) inflammation
• Poor nutrition
• Inactivity
• Molecular changes associated with aging
• Slowed muscle healing due to weakened skeletal muscle stem cells
• Degeneration of connections between motor nerve cells and muscle
• Hormonal changes

Loss of muscle mass is a serious threat to health, and it contributes to disability and frailty in adults who are older. In addition, some research indicates there may be an association between sarcopenia and rheumatoid arthritis.

Building Muscle

Preserving muscle mass is essential to health for people who are aging. A healthy diet and regular strength exercise can be effective. Christmas stresses that joining a gym or hiring a trainer isn’t necessary. A person can build muscle using their body weight (e.g., by doing push-ups and squats) and lifting household items such as soup cans.

Improving balance and flexibility by strengthening core muscles (chest, back, belly, hips, glutes and thighs) and careful stretching can help prevent falls, which Christmas cites as major causes of disability and death.

“I recommend my patients do everything they can to avoid a serious fall, including maintaining strength and flexibility, wearing sturdy, stable shoes and being very cautious when walking the dog, traversing icy walkways, going up and down stairs, using ladders and performing other risky actions.

“After a bad fall,” she says, “life is never the same.”

Is it safe to lose weight after age 65?

It can be if you work with your doctor. But Christmas says she’s careful to ascertain her patient’s reason for wanting to lose weight, and she discusses realistic goals and potential risks before prescribing any diets or changes.

“We need to focus on helping people get healthier and more functional,” she says.

“For instance, while I look at the patient’s weight and weight trends, their functional status is the most important thing. I’ll ask them if they think their weight is impairing their health in any way, or if they think their knees felt better when they weighed less.

“If I do suggest a weight loss plan, it is to address a diagnosed health problem where obesity can be a contributing factor, such as sleep apnea, arthritis in knees, diabetes or hypertension.”

Weight Loss for Adults Who are Older

If a patient is at risk because of one of these conditions, Christmas says she approaches weight loss with what is most likely to work for the individual.

“We start with a careful diet history,” she says. “People often say they have not increased their caloric intake, yet they have gained weight. This makes sense, because metabolism changes as we age, and we cannot at 65 eat the way we did at 25 without weight gain.

“We look at the American diet, which is typically lacking in fiber, lean protein, fruits and vegetables. I try to steer patients who want to lose weight toward a more plant-based approach to eating, such as the Mediterranean diet or even a vegetarian or vegan lifestyle.

“A person can ― and should ― have an occasional treat now and then to enjoy life, but in moderation.”

Regarding exercise, Christmas says, “I ask the patient what they like to do in terms of activity, and I recommend slow changes over a long range to increase exercise with a focus on muscle building.”

She also discusses other aspects of lifestyle with patients, especially sleep.

“Healthy sleep contributes to brain health, memory and physical vigor, and helps regulate metabolism and hormones, including those that affect appetite and satiety,” Christmas says.

Weight Loss Drugs and Adults Who Are Older

Christmas says the arrival of weight loss drugs has brought many patients to her office hoping she will prescribe them. But she is cautious about doing so.

“Taking someone who has lost muscle mass due to aging and giving them a drug to lose weight can be very dangerous,” she says. “Dieting and using weight loss drugs causes loss of both muscle and bone mass. Without exercise, using these drugs is not going to help the person in the long run. They are likely to gain fat back.”

“If a patient has diabetes, heart disease or other illness associated with weight,” Christmas says, “I may make an exception and prescribe weight loss medications, but always in conjunction with a lifestyle change.”

BMI and Body Image in People Over 65

Christmas observes that some of her patients who are older seek her advice about losing weight because they feel that extra body weight detracts from their appearance. Christmas says she tries to provide perspective on the impact of a healthy weight on overall health and encourages them to let go of unrealistic goals perpetuated by the media. 

“Stigma around weight is awful,” Christmas says, and defining it by BMI is not helping. “Discrimination based on ethnicity, gender and age may pressure people 65 and older to lose weight quickly to achieve some sort of ideal appearance promoted by the consumer market.”

She gives a hypothetical example of a patient with a BMI of 27 who wants to get back to the pants size she wore at age 30.

“If this person is over 65, she may be in good health at her current weight, especially if she is active and has strong muscles,” Christmas says.

“Building muscle mass can mean a higher number on the weight scale,” she says, “but it’s good weight ― pounds that can keep an older adult active and safer from falls.”