Your mom may be a tad bit overweight, so you will be, too, right? Not necessarily. Although biology does help determine our physical makeup, how you treat your body is really the key to whether you maintain a healthy weight or not. Most likely, you'll go through phases where shedding pounds is more difficult.

Science says our fat cells (particularly those of women) are subject to life changes, and the process of trying to keep trim usually starts in college, when we tend to spend more time boozing and less time snoozing. In fact, the average freshman-year weight gain is 8 pounds, a study from Purdue University in West Lafayette, Indiana, finds. What's more, as young women age, they exercise 15 percent less and their weight increases by 21 percent over 20 years, research from Kaiser Permanente in Oakland, California, reveals. Take this quiz to determine your fate ... then use these age- and shape-specific tips to become a diet success.

IF YOU'RE IN YOUR 20s...
You may be in the best shape, but your toned tush is spending most of its time planted firmly in a chair. Forty-one percent of women add weight during their 20s, due in part to more sitting, the Australian Longitudinal Study on Women's Health notes. To help outsmart the spread, do 30 to 60 minutes of cardio five times a week (walking counts!).

If you're trying to peel off a few pounds, make those sweat sessions more intense and aim to burn at least 300 calories per outing. Proof that exercise is key to weight loss: People who upped their daily calorie burn by 20 percent lost 17 pounds in a year, about the same as those who cut dietary intake by 20 percent, but the exercisers preserved more metabolism-revving muscle, a study from the Washington University School of Medicine in St. Louis finds. Discover great perfect-for-you fitness plans at Self.com/fitness.

IF YOU'RE IN YOUR 30s...
By this decade, you've probably changed jobs, become a parent (congratulations!) and, in the process, lost some muscle tone. This means a dip in your metabolism. Make sure to exercise to help head off fat gain (staying sedentary puts you at risk for trading 1/3 pound of muscle for fat per year) and add in strength training to your routine. Try to do two 20-minute bouts of toning weekly to maintain muscle; three 40-minute bouts to build it (in addition to your regular cardio sessions). Lean muscle is more compact than fat, and it burns more calories every minute of the day (and night). So not only is it easier to melt off pounds, but your clothes will fit better, too.

IF YOU'RE IN YOUR 40s...
As responsibilities increase in this decade (mortgages? older parents?), estrogen levels decline and some of the fat that padded hips for child bearing now relocates to your abdomen. Continue to exercise consistently, integrating both cardio (which helps burn off belly fat, a heart disease risk) and pilates, which works your core.

IF YOU'RE APPLE-SHAPED...
When your silhouette is apple-shaped, you carry most of your weight around your middle, where it's riskiest to your heart. The good news? You don't have to surrender your favorite bites to whittle your waistline. A regular exercise routine can keep your belly fat at bay.

That said, you need to be mindful about preventing heart disease. Visceral fat—the deep abdominal kind that packs around vital organs—drops excess fatty acids into your bloodstream that are then delivered to and stored in the liver, where they can interfere with the organ's ability to regulate glucose and insulin levels. Excess insulin is linked to increased blood pressure, cholesterol and triglycerides levels, all of which contribute to heart disease and diabetes.

To lose ab fat pronto and stay heart-healthy, make sure to schedule regular sweat sessions. Jogging an average of about 30 minutes a day led to a 7 percent reduction in visceral and total belly fat in eight months, according to a study at Duke University in Durham, North Carolina. That translates to a 1 1/4-inch loss at the waist!

IF YOU'RE PEAR-SHAPED...
Hold most of excess baggage on your hips and thighs? You might feel self-conscious—pear-shaped women tend to be more down on their body than those with applelike figures, a study from Yale University in New Haven, Connecticut, finds—but fat concentrated on the lower half seems to be a safe depository for triglycerides, lipids (blood fats) that harm the heart when levels get too high. Another confidence boost: Guys find pear-shaped women more attractive than those with less full hips, research at the University of Texas at Austin notes.

To stay healthy and maintain a healthy weight in the process, stick to regular cardio and fit in toning to help trim your hips. Cardio burns fat all over; toning your upper body can help deemphasize hips. Try head-to-toe firmers. One of my favorites to build arm, shoulder and chest: Begin in plank position, hands on floor beneath shoulders, resting on toes. Walk hands back toward feet as far as you can comfortably go (you can bend your knees). Hold, then walk hands back to start. Repeat five times.