Your Mum Was Apple Shaped
A lot of what determines where you store fat comes down to genetics. A quick look at your family tree should reveal if your clan tends to be apple-shaped or pear-shaped. Those whose genes push them into the apple category may have to be extra diligent about getting lots of physical activity and limiting their calorie intake if they want to stop their bellies from protruding.
Your Hormones Are Shifting
Around menopause, even formerly pear-shaped women—who carry most of their weight on their hips and thighs—often notice that their bellies start to grow. A drop in estrogen, coupled with your metabolism naturally slowing a bit as you age, is likely to blame. Building more muscle through strength training (and concentrating on your core) should make a difference.
You Have PCOS
Polycystic ovary syndrome affects around 10 to 20% of women during their reproductive years. These women have higher than usual testosterone levels and also often find themselves gaining weight, especially around the middle. Since men are more likely to be apples than pears, it's thought that those high testosterone levels might cause this typically "male" pattern of weight gain. Other PCOS symptoms include irregular periods, excess body hair, and acne. If you suspect you might have this condition, talk to your doctor; you may need medication.
You're Not Getting Enough Sleep – Or You're Sleeping Too Much
You just can't win! Regularly getting 5 hours of sleep a night or less has been linked to an increase in belly fat, but so has getting 8 hours or more. "We still have a caveman's physiology," Andersen says. "If we're sleep deprived, our metabolism will decrease to preserve energy, and we'll eat things we know we shouldn't." The search for easy energy in the form of fries or a doughnut is a relic of primitive days, when our early ancestors literally didn't know when they'd be able to eat next. That's why their bodies stored those quick calories as fat, particularly around the middle, she explains.
Researchers aren't exactly sure why those who slept a lot also put on extra belly fat, but it's possible that more time in bed equals less time being active. Everyone's sleep needs are different, but your sleep sweet spot is probably between 7 to 9 hours a night.
You're Seriously Stressed
Experts have long known that frazzled folks are more likely to accumulate belly fat; now they're learning more about why. When you're under pressure, your body pumps out cortisol, a hormone that wreaks havoc in at least two ways. For starters, it makes you more likely to seek out fatty, sugary foods that provide quick comfort. Cortisol also alters your body chemistry so you burn off fewer of those calories (and store more as fat), says Andersen.
Although an annoying e-mail from your boss might have sent you into a tailspin, the resulting cortisol spike is another vestige of earlier times when a sense of panic signaled an actual life-or-death situation. Everyone gets stressed on occasion, but if feel like you're chronically in fight-or-flight mode it might be time to get help —or at least a good yoga class.