It can be so discouraging when the news media splashes photos of new celebrity moms who’ve lost every trace of their after-baby weight in lightning-fast speed. Try to remember, these women often have advantages most new mothers don’t: personal trainers, private gyms, private chefs, live-in nannies, flexible schedules, and such. For the rest of us, a new study from the Mayo Clinic suggests that focusing on just one number — 27 — can be the key to a lifetime of health. Think 27 when losing after-baby weight and all other diet-crazy numbers lose significance.

Pregnant woman on scale

The number 27 represents a healthy waist measurement for adult women, according to Dr. James Cerhan, an epidemiologist and lead author of the Mayo study. When a woman’s waist measures no more than 27 inches, she is much less likely to develop chronic diseases such as cancer, heart disease, and respiratory ailments that zap years from a woman’s lifespan.

The body mass index (BMI) has long been used as a measure of health but Cerhan says that even women with healthy BMIs but waistlines bigger than 27 inches are at increased risk for these chronic diseases.

Cerhan and his research team pored through the data from 11 studies involving 650,386 white adults between the ages of 20 and 83 years. They enrolled in the studies between 1986 and 2001.

The researchers discovered that women with waistlines 37 inches in circumference or greater were 80% more likely to die early than those with waistlines of 27 inches. This difference represents a loss of five years to their life expectancy once past the age of 40.

The danger doesn’t wait until the waistline is ten inches too big. Cerhan says it’s incremental. His study indicates every two inches above 27 puts a woman at 9% higher risk for life-shortening chronic illness.

Dads who gain sympathy weight during mom’s pregnancy aren’t off the hook either. The magic waistline number for adult men is 35. When a man’s waistline creeps past the 43-inch mark, his risk of mortality increases by 50%, and as with women, the danger grows in increments as the once-35-inch waistline expands.

Cerhan says the reason waist measurement is more predictive of disease than the BMI is that the BMI is a head-to-foot assessment of weight. Fat that accumulates around the belly is metabolically different than fat deposits elsewhere in the body and is a more reliable predictor of future diagnosis of diabetes and heart disease.

Losing even a few inches of waistline “could have important health benefits,” according to Cerhan. He urges physicians to evaluate both BMI and waistline measurement when assessing a patient’s health.

Source: Cerhan, James R. “A Pooled Analysis of Waist Circumference and Mortality in 650,000 Adults.” Mayo Clinic Proceedings. Mayo Clinic. Mar 2014. Web. Mar 18, 2014.