Always Take These Supplements On An Empty Stomach

The question of whether to eat or not before taking your supplements is an important one that often gets overlooked. While you can take some supplements more or less whenever, others either serve your body better when consumed on an empty stomach or settle best alongside food. Fail to follow these best practices, and you might not absorb your supplements well (or get stuck with annoying side effects). So, which supplements should you take on an empty tank? Here’s an expert-backed cheat sheet.

• ABOUT OUR EXPERTS: Katherine Maslen, N.D., is a naturopathic doctor and host of The Shift podcast. Kaytee Hadley, M.S., R.D.N., I.F.M.C.P., is a functional medicine dietitian and founder of Holistic Health and Wellness in Richmond, VA.

1. Iron

You could say the guidance around when to take iron is pretty, well, ironclad. As far back as the 1970s, studies have indicated that food (especially certain types of food) can inhibit the body’s ability to absorb this critical mineral.

“Iron is best taken on an empty stomach, away from other supplements, drugs, and food,” confirms Katherine Maslen, N.D., naturopathic doctor and host of The Shift podcast. “If you take iron with a meal, it could interfere with the absorption of other nutrients in the food, and vice versa. Taking it on an empty stomach gives it the best chance of maximum absorption.” 

While eating stimulates stomach acid (which helps with the absorption of non-heme iron, the type found in supplements), the presence of certain foods and nutrients (particularly calcium, zinc, and phytates) in the digestive system can keep your body from absorbing the iron, which is why many experts recommend taking the mineral solo.

One exception to this rule: “If you’re struggling with iron deficiency, taking vitamin C with iron supplements and iron-rich foods can help boost absorption,” says Kaytee Hadley, M.S., R.D.N., I.F.M.C.P., functional medicine dietitian and founder of Holistic Health and Wellness in Richmond, VA.

2. Folic Acid

Among the many B vitamins, folate (a.k.a. vitamin B9) is one of the best-known. A water-soluble nutrient, it’s famous for preventing neural tube defects in babies during pregnancy. As such, the CDC recommends all women of childbearing age take 400 micrograms of folic acid—the synthetic form of folate—every day.

Read More: What’s the Difference Between Folate and Folic Acid?

According to Maslen, folic acid can technically be ingested with or without food, but you’ll likely absorb it more efficiently on an empty stomach—and the impact could make a real difference over time. The National Institutes of Health reports that only 85 percent of supplemental folic acid is bioavailable (i.e., absorbable) when taken with food, while 100 percent is absorbable when taken without it.  

3. Vitamin C

In general, the body doesn’t have a hard time using up moderate amounts of vitamin C, Maslen says. However, taking it on an empty stomach may lead to more rapid absorption. Some research has shown that the lumen (part of the small intestine) absorbs less of this important antioxidant when it’s full of food.

Another consideration here: “Your body can only absorb around 250 milligrams of vitamin C at a time,” Maslen says. “Most supplements contain 1,000 milligrams—but you will never absorb that much in one go.” The workaround? Take smaller doses of vitamin C every few hours, ideally between meals, she advises.

Read More: 10 Sources of Vitamin C That Aren’t Oranges

The Bottom Line

Generally, it’s important to follow your healthcare provider’s guidance for supplement timing. With certain supplements, dosing with food versus an empty stomach really matters—but it’s okay if you can’t always attain perfection. Timing your supplements right is a good move for getting the most bang for your buck and avoiding any potential tummy troubles, but as Hadley says, “the best time to take your vitamins is when you’re the most consistent.”

This article was reviewed by Brian Tanzer, nutritionist and Director of Scientific and Regulatory Affairs at The Vitamin Shoppe.