Short answer: Lactobacillus acidophilus is a lactic acid bacterium that lives naturally in people and has been used in cultured milk and probiotic supplements for more than a century. Its name means "acid-loving". Like every probiotic species, it comes in many different strains, and a label that names the strain tells you much more than one that just says "acidophilus". Natren's strain is L. acidophilus NAS, found in Megadophilus, Healthy Trinity and several other Natren products.
What is Lactobacillus acidophilus?
L. acidophilus is a rod-shaped bacterium that turns sugars, including the lactose in milk, into lactic acid. That's where the "acid-loving" name comes from: it grows comfortably in acidic conditions that many other microbes don't like.
- Where it's found: naturally in the human body, and in some cultured milks and fermented foods.
- What it needs: it does best without much oxygen and at around body temperature.
- What it makes: lactic acid, the same acid that gives yogurt and cultured milk their tang.
A short history
A pediatrician, Ernst Moro, first described the bacterium in 1900 and called it Bacillus acidophilus. It was later moved into the genus Lactobacillus. By the 1920s, "acidophilus milk" was being sold in the United States, and acidophilus has been one of the best-known names in probiotics ever since.
In 2020, scientists split the very large Lactobacillus genus into 25 groups, and many familiar probiotics got new names. L. acidophilus kept its name.
Why the strain matters
"Acidophilus" on a label names only the species. Within that species there are many strains, and they can behave differently. That's why research on one strain can't simply be applied to another. A full name has three parts:
- Genus: Lactobacillus
- Species: acidophilus
- Strain: a code such as NAS that identifies one specific culture
When you compare acidophilus products, look for the strain code, the count of live cultures (CFU) and whether that count is guaranteed through the expiration date or only "at time of manufacture". Our strain guide explains all of Natren's strain names.
Natren's NAS strain
Lactobacillus acidophilus NAS is Natren's acidophilus strain. Here's what Natren does with it:
- Grown by Natren. Natren cultures its probiotics in its own manufacturing facility in California.
- Supernatant fortified. In Megadophilus, the culture medium NAS is grown in, called the supernatant, is kept in the finished product rather than filtered out.
- Kept cold. NAS products are refrigerated at Natren and shipped cold, and should be kept refrigerated at home, not frozen.
- Counts guaranteed through expiration. Natren guarantees the label's minimum counts through the expiration date when the product is stored as directed.
Which Natren products contain NAS
- Megadophilus, the single-strain NAS product, at 2 billion CFU per capsule or per 1 g serving of powder. Choose dairy capsules, dairy-free capsules, dairy powder or vegan powder. Natren's product copy describes Megadophilus as supporting digestive health and a healthy intestinal environment.*
- Healthy Trinity, with 5 billion CFU of NAS per capsule alongside B. bifidum Malyoth and L. bulgaricus LB-51, in an oil-based capsule.
- Ultimate Vaginal Health Support, with 5 billion CFU of NAS per capsule.
- The Healthy Start System, which includes Megadophilus with Bifido Factor and Digesta-Lac, each in its own bottle.
- For pets: Caninedophilus for dogs and Felinedophilus for cats combine NAS with Enterococcus faecium in an easy-to-give gel.
Comparing these side by side? See the Megadophilus collection or browse all dairy-free and vegan options.
How to take and store an acidophilus probiotic
- Follow the label for the serving size and timing. Powders mix into unchilled filtered water.
- Be consistent. Taking it at about the same time each day makes it easier to remember. Our guide to the best time to take probiotics covers mornings, evenings and meals.
- Keep it refrigerated if the label says so, with the lid tight, and away from heat. Read why in our stomach acid and storage guide.
FAQ
Is acidophilus the same as a probiotic?
L. acidophilus is one species of bacteria. "Probiotic" is the broader term for live microorganisms taken as food or supplements. Many probiotics contain acidophilus; many contain other species, or several.
Does yogurt contain acidophilus?
Some yogurts do, but not all. Yogurt is defined by two other cultures, L. bulgaricus and S. thermophilus, and acidophilus is sometimes added. Check the label for "L. acidophilus" in the list of cultures. Read more in What Is Bulgarian Yogurt?
Is there a dairy-free acidophilus?
Yes. Megadophilus comes in dairy-free capsules and a vegan powder.
Can I take acidophilus with other probiotics?
Many people do. Healthy Trinity combines NAS with two other strains, and the Healthy Start System packages three single-strain products together. If you take medicines or have a health condition, check with your healthcare provider first.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
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