Chewing gum seems like such a harmless — no, even smart — habit.

You want something sweet? Pop a stick of gum for less than 5 calories (better than a candy bar, right?).

Stressed? Chew a couple of sticks of gum (preferable to chewing out a co-worker, no?).

Feeling hungry? Chomp some gum while you think about your options (as in, hit the brakes before you end up knuckle-deep in the chips).

What’s not to like? You may want to consider the following before you reach for that next stick:

You’ll eat less fruit and more junk food: Chewing gum before a meal is often recommended as a way to reduce hunger and eat less.

But a recent study published in the journal Eating Behaviors debunks this belief. The study showed gum chewing not only had no effect on calories consumed, but chewing mint-flavored gum reduced the intake of healthy food (fruit) and increased the likelihood of eating junk food such as potato chips and candy.

Researchers believe the minty flavor of the gum gave fruits and vegetables a bitter flavor. Try sipping a cup of green tea before a meal to curb your appetite instead, which can even help you lose weight.

It can trigger TMJ: Chewing gum can lead to symptoms of temporomandibular joint disorder (TMJ), which includes jaw pain associated with the chewing muscles and joints that connect your lower jaw to your skull. Ouch.

Overuse of any muscle and joint can lead to pain and problems. Many people end up with contracted muscles of the jaw, head, and neck, which can lead to headaches, earaches, or toothaches over time.

Eat an apple instead, which satisfies the urge to chew and reduces your risk of cardiovascular disease at the same time.

You could develop GI problems: Irritable bowel syndrome (IBS) is a GI disorder characterized by abdominal pain, cramping and changes in bowel habits.

Chewing gum can contribute to IBS, as excess air can be swallowed, which contributes to abdominal pain and bloating.

In addition to swallowing air, artificial sweeteners such as sorbitol and mannitol can cause diarrhea in otherwise healthy people.

You’ll rot your teeth: In an effort to avoid the laxative effect of artificially sweetened gum, switching to sugar-sweetened gum may sound logical, but it’s fraught with its own issues.

Sugar-sweetened gum bathes the teeth in sugar and is a source of tooth decay.

You’re chewing a sheep by-product: Lanolin, an ingredient found in skincare products, keeps chewing gum soft.

It doesn’t sound too bad until you find out it’s a yellow waxy substance secreted by the sebaceous glands of sheep. Known as “wool fat,” lanolin is harvested by squeezing the sheep’s harvested wool between rollers.

In the amounts used in chewing gum, it hardly poses a threat to your health, but the thought of digesting it may be a bit unsavory.

You’re releasing mercury into your system: Silver fillings known as amalgam dental fillings consist of a combination of mercury, silver, and tin. And research shows that chewing gum can release the mercury from the fillings into your system.

The problem? High levels of mercury can cause neurological issues as well as chronic illnesses and mental disorders.

Fortunately, the small amount released through dental fillings isn’t likely to harm you, as it typically passes easily through your intestinal tract. That said, do you really want metal in your body?