“If you ingest caffeine on an empty stomach, it will have a more potent stimulant effect that will also tend to increase the level of jitteriness that caffeine can produce,” Stanford neuroscientist Andrew Huberman, Ph.D. notes on the Huberman Lab Podcast.
And some coffee drinkers are going to feel this more than others. “Some people are going to be very sensitive to coffee triggering an insulin response, even if the coffee is black or only has fat, but no sugar,” Pedre says. “When the pancreas releases insulin, blood sugar will drop subsequently. And within 30 to 60 minutes of drinking coffee, a blood sugar drop will cause uncomfortable weakness, shaking, and cravings for carbs or sugar.”
These regular crashes could have long-term impacts. “It may even lead to the overconsumption of calories over the rest of the day,” Pedre says, “which will cause weight gain in most individuals.”
If you experience these “crash” symptoms, you may wish to wait until you break your fast to drink your coffee. Alternatively, you could wait until just 30 minutes before you break your fast, Pedre adds. That way you can use food to mitigate any blood sugar plummet. Another potential way to limit a crash is to add MCT oil and ghee to your cuppa. Huberman also says adding 100 mg of l-theanine can offset some of the jitteriness.
Another potential side effect of drinking coffee on an empty stomach is gastrointestinal upset. “Coffee on an empty stomach can trigger the release of hydrochloric acid33,” Pedre explains, “leading to an acid stomach, heartburn, and acid reflux.” Excessive coffee consumption in a fasted state, over time, can also lead to abdominal pain and nausea, he adds.
If you have a history of gallbladder attacks, you may wish to avoid coffee, especially on an empty stomach. “Coffee induces the release of a hormone called cholecystokinin34 [CCK],” Seeman adds, “which causes gallbladder contractions. People with underlying gallstones can get symptomatic with ingestion of coffee.”
Finally, be aware of how much coffee you consume and if you have any restrictions on caffeine intake regarding underlying conditions. “Excessive caffeine intake has risks35, including poor sleep, high blood pressure, headaches, anxiety, and more,” Seeman notes. “The recommended upper limit of caffeine is no more than 400 milligrams per day for adults.”