You eat the same as you always have. Your exercise program hasn’t changed a bit. Yet your favorite jeans are getting tighter. What could be causing this? Tiffani Bachus, R.D.N., and Erin Macdonald, R.D.N., discuss the many factors that could cause you to gain weight even if your daily habits haven’t changed.

1. Age.

As you age, there is a natural slowdown in metabolism due to loss of lean body mass. A reduced metabolism means your body is burning fewer calories than it used to. If you’re still eating the same number of calories as you did when you were younger, you’ll gain weight. It’s simple math: calories in vs. calories out.

2. Sleep.

A number of studies have shown that inadequate sleep (less than 7.5 hours a night) messes with the hunger and fullness hormones. Less sleep makes you feel hungrier and slower to feel full, so you end up eating more than you normally would to satiate yourself. Try to hit the hay a little earlier so you can log the sleep you need to stay healthy and trim. The sweet spot is 7.5-9 hours of shuteye.

3. Stress.

If you’re under a lot of stress (and who isn’t?), your body pumps out excess amounts of cortisol, the stress hormone, which has been linked to increased fat storage, especially around your middle. Consider adding in some deep-breathing exercises or meditation to help lower you stress level. If you’re new to meditation, start off by taking two minutes a few times a day to shut your eyes and breathe slowly and deeply. You will be amazed at how much better you feel.

4. Exercise.

If you have been doing the same exercises day in and day out, your body has likely trained itself to perform them and actually burns fewer calories during that workout session. If you think of yourself as a cardio queen (or king), consider hitting the weights. Weight training stimulates your lean muscle mass, increasing your metabolism. Also, high-intensity interval training (HIIT) can help your body burn more body fat as a fuel source throughout the day.

5. PCOS.

Polycystic ovarian syndrome is a condition of hormonal imbalances in women that leads to insulin resistance and increased body fat. Other markers of PCOS include cystic acne, increased facial hair, infertility, and a high number of ovarian cysts detected by ultrasound. If you’re concerned, get your hormone levels checked and have the doctor look at your ovaries with an ultrasound.

6. Hypothyroidism.

The thyroid, a butterfly-shaped gland in your neck, is responsible for regulating your metabolism. If the thyroid is not producing enough thyroid hormone, your metabolism slows down. Taking thyroid-replacement medication controls most cases of hypothyroidism, but some can be fixed with dietary changes. Food sensitivities can be linked to thyroid disorders.

7. Alcohol.

A drink here, a drink there and those calories really add up. Have you ever heard the term “beer belly”? They call it that for a reason. Also, drinking decreases your inhibitions, making it easier to nibble on the nachos and throw back some bar nuts.

8. Smoking.

For those of you who have kicked the habit, congratulations! Unfortunately, however, smoking’s appetite-suppressing powers are now gone and you’re feeling hungrier than normal. Couple that with your taste buds no longer being dulled by the nicotine. When everything tastes better, your hunger increases and you eat more calories than you used to, which leads to weight gain.

9. Prescription medications.

A number of prescription medications—for conditions like blood pressure, diabetes, depression, anxiety, bipolar disorder—have the unfortunate side effect of weight gain. Some do so by slowing your metabolism, while others increase your appetite. Always ask your doctor or pharmacist about these side effects and if there are any other prescription options that don’t have these side effects.

10. Microbes.

Approximately 70 percent of your immune system is in your gut, so what you eat greatly impacts your immunity. A typical Western diet—highly processed, high-sugar, high-fat and low-fiber—has altered the bacteria in our gut flora, which is linked to weight gain. Other modern assaults on the gut include the overuse of antibiotics, acid blockers, anti-inflammatory medication, aspirin and steroids. Improving the quality of your diet with whole, fresh, in-season, high-fiber foods can dramatically reduce inflammation and help support healthy flora in your intestine. Get rid of the bad bugs, drugs and food allergens and replace them with prebiotics, probiotics, fiber and enzymes. Other functional supplements that repair the gut lining are; omega-3 fats, glutamine, quercitin and zinc.

11. Inflammation.

Inflammation is part of the body’s natural defense system. But chronic (long-term) inflammation caused by poor food choices, allergies and sensitivities make you gain weight by excess swelling and fluid retention in your tissues. Identifying your “trigger” foods and then following a structured eating plan tailor-made for your individual sensitivities is a proven way to help you shed those unwanted pounds and clear up a whole host of symptoms that keep you from feeling your best.

This article originally appeared on urockgirl.com.