A new study explores the effect of both high BMI (body mass index) and greater waist circumference on all-cause mortality for people over 65 years of age.
The study found that a BMI indicating overweight is associated with a 46% reduction in the risk of all-cause mortality for males and that class I and class II obesity are associated with a 51% lower risk.
Having an underweight BMI or being a normal weight with a high waist circumference were linked to a higher risk of all-cause mortality in both men and women.
In addition, the study reported that a high waist circumference in men was associated with a 24% higher risk of all-cause mortality, compared to people with a healthy waist size. A similar effect was seen in women.
A higher waistline measurement often indicates problematic body fat around the kidneys, liver, heart, pancreas, and digestive organs.
The study, published in theJournal of the American Geriatrics Society, incorporated data from a cohort of 6,905 individuals ages 65 years and older from 2011 to 2024.
A person’s BMI is a numerical value derived from their height and weight as a means of predicting their amount of body fat. Body fat, in general, is linked to health issues.
BMI values are associated with body-type descriptors, including the class I and II categories of obesity cited in this study, as well as underweight, healthy, and overweight.
However, BMI alone is not necessarily an indicator of health. For example, a short, muscular person may have a high BMI while being in excellent health.
“It has long been recognized,” said Mir Ali, MD, “that BMI is not an ideal measure, and that a high waist circumference, which typically indicates truncal obesity, is a better predictor of mortality risk.” Ali is the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, and was not involved in the study.
In addition, a loss of muscle mass and bone mineral density that may occur with age can result in a lower BMI. This means a higher BMI may indicate better muscle mass and bone density.
Older people with illnesses or chronic conditions may also have lost weight, resulting in a lower BMI, which may be reflected in the study.
“Patients with class I or II obesity and a normal waist circumference typically carry most of their weight in their hips and thighs, maintaining a relatively normal torso. Individuals who carry their weight in the lower body likely experience less impact on their internal organs.”
— Mir Ali, MD
Some of the study’s results are surprising, as they indicate other factors may be at play.
“There are some surprises, especially with the paradox of the seemingly protective effect of class I and class II obesity on male mortality independent of waist circumference,” said Jayne Morgan, MD, cardiologist and Vice President of Medical Affairs for Hello Heart, who was also not involved in the study.
Morgan suggested, “In [older adults], some weight may actually be protective.”
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“In fact,” she surmised, “this may actually be less of a healthy state and more of an indicator of less frailty, less debilitating illness, and lack of terminal illnesses that often portend severe weight loss.”
“More weight, therefore, seems to confer a survival advantage,” she said.
Morgan also touched on the health risks associated with being underweight.
“[The study] lends further evidence that being underweight, regardless of waist circumference, portends the highest mortality risk,” she added. Morgan considers this “especially important in the era of potential GLP-1 abuse and body dysmorphism, especially among women.”
The study’s finding of an association between high waistline measurements and increased mortality is less surprising.
Morgan warned that a waist increase of 2–3 inches in perimenopausal and menopausal women may be especially concerning.
It, she said, raises “the specter of increased cardiometabolic risk and all of its inherent health challenges, including increased insulin resistance, increased cholesterol, pro-inflammatory state, and increased cardiac and stroke risk.”
Waistline circumference is derived by measuring the waist between the lower rib and the iliac crest, the upper border of the buttocks.
A high waistline circumference is defined as 40 inches or more in men and 35 inches or more in women.
Morgan pointed out that the study found that class I and II obesity did not confer a significant mortality advantage in females. “However, interestingly, being overweight did.”
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She said that BMI can be especially misleading as a marker of female health, noting that several high risk body types “fly under the radar” using BMI.
Morgan cited the “skinny fat” female: “This is the female with a normal weight, and normal BMI, but a fat redistribution from the hips to the abdomen. This increased visceral fat carries a higher metabolic burden and higher cardiovascular risk, but the woman is classified as normal despite the increased waist circumference.”
She also reported that heart-transplant BMI guidelines often wind up excluding Black women.
“Many of these women,” she said, “exhibit the healthier body fat distribution of a smaller waist circumference and rounder hips. This pear-shaped body for females, with weight being carried in the bottom and hips, is the healthier distribution, yet many have been denied heart transplants in part because of this metric.”
