If you’ve ever had trouble losing weight, you’ve probably placed at least some of the blame on a slow metabolism. It’s true that your basal metabolic rate — the rate at which your body uses energy — can affect your ability to shed pounds. But there are also a few external, controllable factors that can slow down that metabolic rate, says Michael West, MD, an endocrinologist with Washington Endocrine Clinic in Washington, D.C.

Here are eight triggers that can slow metabolism, some (but not all) of which you can control, to make sure you aren’t sabotaging your weight-loss efforts.

1. Age. As you get older, your ability to quickly use up energy diminishes and your metabolism can slow. “As cells age, they do metabolize less rapidly,” Dr. West says. Older people also tend to have less muscle mass than younger people, which translates to a reduced metabolic rate. While you can’t make yourself younger to speed up your metabolism, West suggests being diligent about getting enough exercise — many people tend to get out of the habit as they age. The Centers for Disease Control and Prevention suggests that adults 65 and older get two and a half hours of moderate-intensity aerobic activity every week and do strengthening exercises on all the body’s major muscle groups at least twice a week.

2. Stress. When your nerves are frazzled, your body releases cortisol, a hormone produced by the adrenal system that is linked to weight gain. “There are definitely established links between psychological stress and the adrenal system,” West says. To make sure that stress isn’t making it harder to take off pounds, try to calm yourself by reducing the controllable stressors in your life. For example, if heavy traffic makes you nervous, avoid the roadways during rush hour. Regular physical activity, deep breathing, and even professional help from a psychologist or counselor may also be helpful.

3. Poor sleep habits. Getting too little shut-eye can significantly alter your body’s processes enough to predispose you to gain weight. “There was a recent study where healthy volunteers were subjected to poor sleep,” West says. “Even over one night, the lack of sleep was significant enough to disrupt their metabolic patterns and give them more insulin resistance, which is a risk factor for diabetes.” Insulin resistance has also been associated with obesity. To increase the chances of boosting metabolism, adults should get seven to nine hours of sleep each night.

4. Lack of exercise. Exercise not only helps you expend more calories while you’re physically active, but there’s also some evidence that it may increase your resting metabolic rate. To make sure you get enough exercise for boosting metabolism, set aside a dedicated period of time, rather than trying to accomplish it during the course of your everyday activities. Adults ages 18 to 64 need about two and a half hours of moderate-intensity aerobic activity each week, as well as strengthening exercises for all muscle groups twice a week.

5. Diet. It may be tempting to severely restrict your calories or skip meals to lose weight, but that may be a self-defeating practice. Not eating enough can actually cause your metabolism to slow down in an attempt to conserve calories. “There’s something to be said for eating a small meal around breakfast time to get your metabolism moving for the day,” West says. “Eating small meals throughout the day can also be helpful.” What’s more, under-eating or meal-skipping can make you more likely to overeat at your next meal.

A few studies have also shown that caffeine-containing drinks like green tea and foods containing capsaicin (a chemical that gives spicy foods their heat) may cause temporary increases in metabolic rates. However, they only increase energy expenditure and fat-burning by a very small amount.

6. Medication. Certain drugs can make it easy to put on pounds and hard to lose them. “Some antipsychotic drugs used for bipolar disorder and depression can make patients put on significant amounts of weight,” West says. One such medication, olanzapine (Zyprexa) has been shown to promote weight gain. Scientists aren’t sure why it happens, West says. If you feel your medications may be causing your body to hang on to extra weight, talk to your physician. He may be able to switch you to another drug that’s less likely to have those unwanted side effects.

7. Weather. There is some evidence that exposure to colder temperatures causes an increase in metabolism, as the body attempts to stay warm. However, research in this area is scarce, West says. People living in cold climates may be more likely to gain weight, he adds, because the low temps have a negative effect on their moods. “When you have long winters, you can have depression, and depression can cause people to gain weight,” West says. If you live in a cold place, be extra vigilant for symptoms of depression, and talk to your doctor if the blues don’t go away.

8. Illnesses. There are some medical conditions that can make losing weight more difficult. For example, thyroid problems like hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone, can cause body functions to slow down and weight gain to result. In men, low testosterone levels can have the same effect. Medications are available to relieve most of these conditions or eliminate their symptoms. If you’ve been trying to lose weight for some time and have been unsuccessful, ask your doctor about screening tests for these conditions.

Increase the amount of exercise you do, get enough sleep, and talk to your doctor about medical conditions that can be affecting your metabolism — these steps may bring about the positive changes you’re looking for.***