Obesity is a public health crisis, with excess fat linked with a wide variety of chronic conditions. Yet our tendency to use body mass as a convenient proxy for unhealthy weight gain may obfuscate the true risks – and even benefits – of being a little bigger.
The results of a recently published longitudinal study conducted by researchers from the University of Rhode Island in the US found that a higher body mass index (BMI) among US adults over the age of 65 years was linked with a lower risk of death.
This doesn’t necessarily mean fat is our friend. The same study showed that once BMI had been taken into account, larger measures of the waist – a sign of excess abdominal fat reserves – were independently associated with a rise in mortality.
“Our findings suggest that considering both measures together, rather than relying on BMI alone, may improve mortality risk assessment and support more informed clinical decision-making,” says study co-author Bryan Blissmer.
The findings add to a growing body of evidence supporting what’s known as the “obesity paradox” among seniors, giving researchers a few extra clues that could help resolve what seems to be a contradiction in health.
Decades of research have cemented links between obesity and heart disease, type 2 diabetes, fatty liver disease, sleep apnea, numerous cancers, osteoarthritis, and poor mental health. So it seems incontrovertible – the bigger we get, the greater the risks.
To cut the odds of developing a health issue, specialists advise tracking our weight, comparing it with figures considered healthy for individuals of a given height.
Of course, building muscle, being pregnant, and retaining fluids are ways we can add weight without adding fat. Yet for the most part, calculating your “body mass” index is thought to provide a solid starting point for maintaining a healthy lifestyle.
There are reasons to think this generalization may not be so simple. Numerous investigations over the years have concluded that as we get older, a BMI between 25 and 35 – considered overweight to low-risk obesity – helps us survive a little longer.
Now, it might be that the additional fat reserves compensate for health risks in the face of certain diseases. On the other hand, it may be a methodological phantom arising from a detection bias or a hidden confounding factor.
After analyzing 14 years of data from 6905 participants in the National Health and Aging Trends Study, the researchers behind this recent study found that men with class I or “low risk” obesity had a 46% lower risk of all-cause mortality compared with people in a normal BMI category. For those in class II, the advantage seemed even greater – a 51% lower risk.
In strong contrast, men who had a waist circumference of more than 40 inches (102 cm) saw a 24% jump in their mortality risk. The numbers were similar for women in the study, for whom 35 inches (89 cm) was the defining limit for a large waist circumference.
Keeping in mind that the measures were self-reported and that older people tend to stick with the same height they’ve memorized since they were 40 (despite losing an inch or two over the decades), the results may come with a touch of bias.
It’s also impossible to know whether the critical difference is in where fat is distributed, or whether a higher BMI means more body fat. Past studies have shown that visceral fat can be a bigger problem than subcutaneous fat, for instance.
“The takeaway from this study is that abdominal obesity, which implies an excess of visceral fat that sits around the organs, is associated with a higher risk of mortality even in individuals whose weight is considered within a normal range,” observes Natalie Shilton, Principal Fellow for the Higher Education Academy and Program Director of the Bachelor of Pharmacology & Toxicology at Griffith University in Australia.
The results could also reflect a significant distinction in weight loss and weight gain among different demographics.
As we age, we lose muscle mass. Those who keep it are less likely to experience falls, have better heart health, and are generally more likely to live longer, healthier lives.
“None of this is permission to put on weight,” warns Garron Dodd, head of the Metabolic Neuroscience Laboratory at the University of Melbourne and Founder and Chief Scientific Officer of Gallant Bio.
Dodd, who wasn’t involved with the study, emphasises the importance of exercise for maintaining strength as we get older. “BMI cannot tell fat from muscle, and after 60, a low BMI often means lost muscle rather than leanness. Protect muscle with resistance training and enough protein.”
Studies like these tell us little in isolation.
But the bigger picture can't be clearer. We all must eat well and exercise to live a healthier life.
Source: Scimex
This study was published in the Journal of the American Geriatrics Society.
