An unfortunate fact of life: it's easier to gain weight as you age. But science has just taken a major step towards explaining why – and it's not about how many six-packs you knock back. Research published in the journal Science has identified a number of cellular changes that encourage the production of new fat cells as we get older.
That's not actually bad news. The findings could eventually lead to new medications that help prevent age-related weight gain. And, in the meantime, there are still plenty of ways to fight your (cellular) destiny.
Why Belly Fat Expands with Age
Previously, scientists believed that when people gained weight – particularly around the midsection – existing fat cells simply became larger. But the new study suggests new fat cells may be continually created instead. A different mechanism of weight gain means researchers may be able to develop new ways of preventing it.
The researchers focused on a special type of stem cell, called adipocyte progenitor cells (APCs), which are found in fat tissue (yes, your fat contains stem cells). During youth and early adulthood, these cells remain largely inactive. But later in life, they gain the ability to transform into fat cells, increasing the number you already have.
Scientists used RNA sequencing to examine each cell's gene activity. The short version? When stem cells from older mice were injected into the fat tissue of younger mice, the number of fat cells increased dramatically. The same thing didn't happen when stem cells from young mice were transferred into other young mice.
The team concluded that ageing causes APCs to become highly active, triggering the production of new fat cells.
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'While most adult stem cells' capacity to grow wanes with age, the opposite holds true with APCs. Ageing unlocks these cells' power to evolve and spread,' says Adolfo Garcia-Ocana, PHD, chair of the Department of Molecular and Cellular Endocrinology at City of Hope and study author. 'This is the first evidence that our bellies expand with age due to the APCs' high output of new fat cells.'
The researchers also found that a signalling pathway unique to older mice activated another type of stem cell, prompting the creation of new fat cells – particularly around the abdomen.
What about humans? The researchers couldn't exactly inject older people's fat into younger volunteers, but they were able to replicate the process using human cells and found similar results to those observed in mice.
Other Changes That Fuel Midlife Weight Gain
Yes, your cells may make gaining weight easier as you age. But they're only part of the story.
Hormones and metabolism change too, says Mir Ali, MD, medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California.
One notable hormone is testosterone. Weight and testosterone are closely linked. Production of the primary male sex hormone naturally begins to decline after the age of 30, making weight gain more likely. Weight gain can also actively reduce testosterone because fat tissue contains an enzyme called aromatase, which converts testosterone into oestrogen.
Then there are the day-to-day lifestyle factors that contribute to the classic 'dad bod'. Richard Siegel, MD, co-director of the Diabetes and Lipid Center at Tufts Medical Center and endocrinologist at Tufts Medicine Weight & Wellness Center–Stoneham, says men in midlife tend to become less active and experience more sleep problems as they age. Both can make gaining weight easier.
How to Get Rid of Midlife Belly Fat
While some men embrace the dad bod, there are proven ways to push back if that's not your goal. The foundations remain the same: diet and exercise. But Men's Health asked obesity specialists for more specific advice on what actually works.
From a nutrition perspective, Dr Siegel recommends eating as much of a plant-based, minimally processed diet as possible.
'This does not have to be a vegetarian diet, though diets higher in red and processed meats have been associated with weight gain.'
And what about beer? The good news is you don't necessarily have to give it up. Instead, he recommends paying closer attention to how much you're drinking. Not only do the calories add up quickly, but alcohol also makes many people more likely to snack.
When it comes to exercise, the ideal approach combines aerobic exercise with resistance training.
'There's nothing you can do to specifically target belly fat,' Ali says.
Instead, the goal is overall fat loss. Cardio helps increase energy expenditure and limit further weight gain, while resistance training helps preserve muscle and improve body composition.
Finally, don't underestimate the importance of a good night's sleep. Consistently getting fewer than seven to nine hours reduces your body's ability to recover properly. That can contribute to a slower metabolism, daytime fatigue that makes exercise less appealing, and increased cravings for high-calorie foods.
'Optimal sleep – quantity and quality – may help to avoid weight gain,' says Dr Siegel.
Ultimately, this latest discovery could one day lead to new medications that target these fat-producing stem cells directly. But those treatments are likely to be years away. In the meantime, the fundamentals of healthy eating, regular exercise and good-quality sleep remain your best defence against midlife weight gain.
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