How Bad Is It Really to Drink Coffee on an Empty Stomach?

For so many of us, coffee is an integral part of our daily ritual and often the first thing we put to our lips in the morning. But some research suggests drinking coffee on an empty stomach isn't the best idea.

How many hours without food is considered an empty stomach? That would be two, per the National Institutes of Health.

So if you brew a pot the moment your eyes open in the a.m., reach for a pour-over when the late afternoon slump hits or power through intermittent fasting on nothing but rocket fuel, we're talking to you.

Here's the latest on how it can affect your health, plus clever tips to mitigate side effects.

Drinking coffee on an empty stomach isn't the best idea because it can lead to some of the following negative effects.

A small June 2020 study in the ‌British Journal of Nutrition‌ found one risk of drinking coffee before eating was impaired blood sugar control.

The ability to regulate blood sugar levels reduces your risk of metabolic conditions like diabetes and heart disease. People who ate breakfast beforehand did not experience a surge in blood glucose.

"Coffee increases your risk of heartburn because it can stimulate acidity in the stomach," says Marvin Singh, MD, director of integrative gastroenterology at the Susan Samueli Integrative Health Institute at UC Irvine and founder of Precisione Clinic.

Coffee is naturally acidic, with a pH between 4.85 and 5.13. Anything under 7 is considered acidic, according to an October 2018 study in ‌Nature‌. This is how coffee can cause acid reflux.

"Although digestive enzymes and gastric juices are released no matter what you consume, food or drink that is acidic in nature — like coffee — can be a gastric irritant, leading to increased acidity in the stomach," Dr. Singh says.

A little digestion 101: When you take a bite of bagel or gulp of water, a valve called the lower esophageal sphincter opens to allow the food or drink to flow from your esophagus into your stomach. Once it enters your stomach, the valve closes again.

But according to the American Society for Gastrointestinal Endoscopy, coffee relaxes that lower esophageal sphincter, causing the valve to not shut completely and allowing stomach acid to seep into your esophagus (a condition called acid reflux).

This can result in the most common symptom of acid reflux, heartburn, which can feel like a sharp pain in your chest. Coffee can also make you nauseous as a result of its high acidity.

If coffee does give you acid reflux, don't ignore it. Coffee can exacerbate stomach ulcers and other digestive issues.

"Long-term, chronic acid reflux from coffee could damage your stomach lining and lead to esophagitis, inflammation of the esophagus," Dr. Singh says. Untreated esophagitis could potentially damage the lining of your esophagus, upping your risk of esophageal cancer.

Dr. Singh also points out acid reflux can be a reaction to mold, an effect that might be magnified if your stomach is empty when you drink up. Regularly clean and descale your coffee maker to help limit symptoms.

Caffeine can make you feel shaky pretty quickly if you drink coffee on an empty stomach. It's absorbed into the body within 45 minutes, and peaks anywhere from 15 minutes to two hours later, according to the Harvard T.H. Chan School of Public Health.

Depending on whether you've already eaten or not, you'll feel the effects faster or slower, especially if you've eaten a fiber-rich meal.

Your genes also play a role in how jittery coffee makes you. A March 2018 report in ‌Coffee & Health‌ found genetic variations determine how your body processes caffeine.

If you have a fast metabolism, drinking a cup of joe is unlikely to make you shaky, but for those who digest caffeine slowly, you're more prone to the jitters whether you've eaten or not.

And if you do tend to get jittery, then drinking java on an empty stomach tends to amplify that effect, Dr. Singh says.

Eating a snack or meal can help quell your quivers, as can opting for a lower dose of caffeine. "Drink half-caf, where you mix half decaffeinated coffee and half regular coffee," Dr. Singh suggests, or use fewer grounds or more water when you make your coffee.

And don't chug your mug. "Drink a cup of coffee over the course of a full hour in order to microdose the amount of caffeine you are getting," Dr. Singh says.

Finally, limit your total caffeine intake. "The rule of thumb for people who get jittery is a maximum of 200 milligrams a day," Dr. Singh says. That's about two 8-ounce cups of home-brewed coffee, per the Mayo Clinic.

Intermittent fasting (IF) — where you restrict the timeframe during which you eat — is associated with a slew of health benefits, from weight loss to lower blood pressure. You can still drink zero-cal beverages like black coffee during food-free hours.

If you're an IF devotee, you might be wondering if you should skip your caffeine fix between meals. "It's a personal decision," Dr. Singh says. "If you feel fine when you have coffee while fasting, then there's nothing to worry about."

On the other hand, if coffee causes stomach pain or makes you feel shaky, then give green tea or half-caf a try. Or spread out your coffee intake by nursing a single serving all morning long.

Whatever you choose, don't forget to drink plenty of water along the way. Caffeine is a mild diuretic, and about 20 percent of the water you need comes from food, according to the Academy of Nutrition and Dietetics. So if you're fasting, you may be low on fluids already. Try alternating sips of coffee and water.

The best time to drink coffee is after you've eaten a meal.

Order your latte in the late morning, shortly after breakfast. If you drink it before you have food in your stomach, you're at risk for all the symptoms mentioned above: a surge in blood sugar, heartburn and acid reflux, jitteriness and the opposite of the desired effect: Coffee can make you tired.

What's more, your cortisol levels peak around 7 a.m., according to the University of Michigan Medicine. Cortisol is a hormone that gives you an energy boost, so unless you're sleep-deprived, you should already be feeling relatively peppy early in the morning.

So, how long after waking should you drink coffee? You'll get the most bang for your buck if you hold off on caffeine for a few hours, once cortisol has started to wane.

On the other hand, you should steer clear of coffee after about 2 p.m. "Having it in the late afternoon or evening could interfere with sleep," Dr. Singh says.

A small November 2013 study in the ​‌Journal of Clinical Sleep Medicine‌​ found getting 400 milligrams of caffeine (about four cups of home brew) six hours before bed slashed sleep time by more than an hour.

In the best of all possible worlds, you'd stick to java with a meal. But if you're sipping it solo and feeling good? You're probably in the clear.

"If you aren't experiencing any symptoms, then I'd say it's OK," Dr. Singh says. "But if you do suspect it is causing a problem, then I would pay attention to that."

Caffeine-sensitive folks should consider eating something before drinking coffee, switching to green tea, drinking half-caf coffee and nursing that coffee slowly in the morning.