They say an apple a day keeps the doctor away. But what about a glass of apple cider vinegar?

As home remedies go, apple cider vinegar is fairly well-known — with supposed benefits ranging from increased energy to improvement of chronic health conditions.

One popular claim is that it's effective for weight loss.

"People are always looking for easy ways to lose weight and improve other areas of their health, and apple cider vinegar is certainly one I'm asked about," says Dr. Neeharika Kalakota, a gastroenterologist at Houston Methodist. "I always say that if you want to try it, try it. But the expectations need to be realistic. And please never drink it undiluted."

What is apple cider vinegar good for?

The touted health benefits of apple cider vinegar include:

• Losing weight
• Preventing type 2 diabetes
• Relieving heartburn
• Lowering cholesterol
• Reducing varicose veins
• Whitening teeth
• Reducing dandruff
• Improving acne
• Boosting energy
  
  

It would be an impressive list — if it were true.

Starting at the top, there's no evidence to suggest that apple cider vinegar helps with weight loss unless it's paired with a calorie deficit — that is, unless you're also eating fewer calories than you're burning.

"Drinking it and then eating a double cheeseburger and fries is not going to work," explains Dr. Kalakota. "There's also no data that it improves weight loss beyond what a calorie deficit already provides."

The claim that apple cider vinegar can relieve heartburn — when stomach acid travels up your esophagus and causes burning pain — is particularly perplexing because, as Dr. Kalakota notes, apple cider vinegar contains acetic acid.

"Consuming it just contributes to the acid in your stomach that's already causing issues," says Dr. Kalakota. "It can actually just worsen acid reflux."

(Related: Is Heartburn Inevitable or Preventable?)

Most of the other supposed benefits are either unstudied or have been debunked, but two areas where apple cider vinegar may play a small role are blood sugar regulation and cholesterol maintenance.

Compilation studies suggest apple cider vinegar may produce a slight decrease in fasting glucose (high fasting glucose is an indicator of type 2 diabetes.) In addition, a few studies showed small increases in high density lipoprotein (HDL), sometimes referred to as the "good" cholesterol — though they showed no effect on low density lipoprotein (LDL), or "bad" cholesterol.

At any rate, these effects are minimal.

"In other words, no, apple cider vinegar won't cure type 2 diabetes or even play a significant role in managing it," says Dr. Kalakota. "It's also not going to help lower your cholesterol or prevent either of these conditions."

Apple cider vinegar side effects: Could it actually be bad for you?

Regardless of whether you buy into its health claims, Dr. Kalakota says the most important thing to know about apple cider vinegar is that it should never be consumed without first diluting it with water.

That's because drinking undiluted apple cider vinegar can cause:

• Erosive dental disease
• Erosive esophageal disease
  
  

"I've had several patients come in who couldn't swallow, and diagnostic endoscopy uncovered that the lining of their entire esophagus was completely raw," says Dr. Kalakota. "When I ask about their diet, I then find out they're taking apple cider vinegar shots every day."

The highly acidic nature of apple cider vinegar is what leads to this damage. This quality is also what causes tooth erosion, which Dr. Kalakota notes is supported by case studies.

"If you are going to drink apple cider vinegar, please always make sure it's diluted," says Dr. Kalakota. "It's also important to drink diluted apple cider vinegar in moderation and, better yet, with a meal."

Otherwise, you risk experiencing not just unwanted but harmful side effects.

How much apple cider vinegar a day is OK?

To reiterate, say no to apple cider vinegar shots altogether.

But also know that diluted apple cider vinegar — one or two tablespoons mixed into a glass of water — should be consumed in moderation.

Dr. Kalakota says it's a good idea to limit yourself to a glass of it per day, though this amount isn't known to bring any health benefit. It's simply a safe upper limit to follow, since having more than this can increase the chances of unwanted side effects, like nausea or worsening heartburn in those who are prone to acid reflux.

"Drinking it in addition to a meal helps," adds Dr. Kalakota. "That way your stomach lining is a bit more shielded from the acid since there's other food there, too."

The case for just eating an apple instead

As Dr. Kalakota mentioned, she doesn't discourage people trying apple cider vinegar — so long as it's diluted and consumed in moderation.

She does point out, though, that there are better, proven ways to achieve its claimed benefits.

"Eating a healthy diet full of fiber and plant products can help with weight loss, managing diabetes, lowering cholesterol and more," says Dr. Kalakota. "If you still want to find a way to incorporate apple cider vinegar, you can certainly cook with it as part of your healthy diet, using it in sauces, marinades and seasonings."

(Related: Eating Healthy: 7 Simple Tips for Getting Started Today)

Also, don't assume that drinking a glass of apple cider vinegar brings the same benefit as eating an apple.

"With a whole apple you get fiber, antioxidants and vitamins," says Dr. Kalakota. "A lot of this is lost when juicing an apple to make cider — you lose the fiber, and many other nutrients get filtered out."

(Related: 7 Benefits of Fiber That Should Convince You to Eat Enough of It)

Fermenting the cider into vinegar doesn't bring back any of those beneficial nutrients.

And while fermented foods may help promote a healthy gut, Dr. Kalakota says there are much less acidic options you can try instead of apple cider vinegar, like kombucha, kimchi and sauerkraut. Another, if you can tolerate lactose, is kefir.

"At the end of the day, if you want to try apple cider vinegar to see if it helps things, try it. But please don't drink it undiluted," Dr. Kalakota reiterates. "And know that it should be paired with a healthy diet, ideally a plant-based one since that's the eating pattern that has the most data behind it."