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 that drinking a cup of java on an empty stomach (defined as two hours before or after you eat, per the National Institutes of Health) isn't the best idea.
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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.
Your Blood Sugar Could Spike
A small June 2020 study in the British Journal of Nutrition found that drinking black coffee on an empty stomach first thing in the morning significantly impaired people's 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.
It Might Trigger Acid Reflux
First, 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 belly, the valve closes again.
But according to the American Society for Gastrointestinal Endoscopy, coffee relaxes the lower esophageal sphincter. The valve may not shut completely, allowing stomach acid to seep into your esophagus, a condition called acid reflux. The most common symptom of acid reflux is heartburn, which can feel like a sharp pain in your chest.
And that's not all: "Coffee also increases the 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, assistant clinical professor of family medicine and public health at UC San Diego and founder of Precisione Clinic.
Case in point: In a September 2020 study in Clinical Gastroenterology and Hepatology, participants who replaced two servings of coffee a day with two servings of water had a reduced risk of 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. An October 2018 study in Nature found that the average pH of coffee is between 4.85 and 5.13 (anything under 7 is considered acidic).
As a result, drinking coffee without food gives you a super strong hit of acidity, turning your stomach into what Dr. Singh calls a "bowl of gastric acids."
The good news: "Eating alkaline foods along with your coffee helps reduce the total acidity level," Dr. Singh says. So make yourself a plate of eggs, avocado toast or oatmeal.
Or switch to green tea, which has a pH of 7 to 10. "It may be less irritating to your stomach," Dr. Singh says.
In addition, he points out that acid reflux can be a reaction to toxins or mold in your coffee — an effect that might be magnified if your stomach is empty when you drink up. "Try an organic, clean coffee, such as Purity Coffee, and see if your heartburn improves," Dr. Singh says.
If coffee does give you acid reflux, don't ignore it. "Long-term, chronic acid reflux could 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.
You Could Feel Jittery
Caffeine is absorbed into the body rapidly — within 45 minutes on average — and peaks in the bloodstream anywhere from 15 minutes to two hours after consumption, according to the Harvard T.H. Chan School of Public Health. You'll feel the effects quicker if you haven't eaten, and the buzz will kick in slower if you've already chowed down, particularly if you had a fiber-rich meal.
Whether you feel anxious and jumpy versus pleasantly alert after gulping that Americano depends largely on your genes, but eating patterns also play a role. A March 2018 report by Coffee & Health found that genetic variations determine how your body processes caffeine. Some people metabolize it quickly, and it has a mild effect on them. Others breaks down caffeine slowly, so the effects are more pronounced and long-lasting.
If you're a fast-metabolizer, drinking a cup of joe is unlikely to make you edgy, even if it has been hours since your last meal.
As for those who digest caffeine at a snail's pace? You're more prone to post-coffee jitters to begin with, whether or not you've eaten recently. And if you do tend to get fidgety, then drinking java with nada in your belly tends to amplify that effect, Dr. Singh says.
While snacking can help quell your jitters, so can opting for a lower dose of caffeine. "Drink half-caf, where you mix half decaffeinated coffee and half regular coffee," Dr. Singh suggests.
And don't chug your mug. "Drink a cup of coffee over the course of a full hour in order to micro-dose 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 mg a day," Dr. Singh says. That's about two 8-ounce cups of home-brewed coffee, per the Mayo Clinic, or one Tall-sized dark roast coffee from Starbucks.
What if You’re Doing Intermittent Fasting?
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 now be wondering if you should skip your caffeine fix in 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 organic coffee, green tea or half-caf a shot. Or spread out your coffee consumption by nursing a single serving all morning long.
Whatever you choose, don't forget to drink plenty of H2O along the way. Not only is caffeine a diuretic, but about 20 percent of the water you need comes from food, according to the Academy of Nutrition and Dietetics. So if you're IF, you may be low on fluids already. Try alternating sips of coffee and water.
When Is the Best Time to Drink Coffee?
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 and jitteriness.
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. 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 November 2013 study in the Journal of Clinical Sleep Medicine found that consuming 400 milligrams of caffeine (about four cups of home brew or a medium-roast Venti at Starbucks) six hours before bed slashed sleep time by more than an hour.
So, How Bad Is It Really to Drink Coffee on an Empty Stomach?
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. Your body is the best doctor."
- Clinical Gastroenterology and Hepatology: "Association Between Beverage Intake and Incidence of Gastroesophageal Reflux Symptoms"
- Nature: "Acidity and Antioxidant Activity of Cold Brew Coffee"
- Harvard T.H. Chan School of Public Health: "Caffeine"
- American Society for Gastrointestinal Endoscopy: "Diet and Gastroesophageal Reflux Disease (GERD)"
- Coffee & Health: "Genetics, metabolism and individual responses to caffeine"
- British Journal of Nutrition: "Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee"
- NIH: "What does it mean to take medicines on an empty stomach?"
- AND: "How Much Water Do You Need"
- Journal of Clinical Sleep Medicine: "Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed"
- University of Michigan Medicine: " Cortisol in Blood Test"
- Starbucks: "Starbucks Coffee Company Beverage Nutrition Information"
- Mayo Clinic: "Caffeine content for coffee, tea, soda and more"
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.