Lactobacillus acidophilus

What it is

Lactobacillus acidophilus is a lactic acid bacterium. Unlike many relatives, it kept the genus name Lactobacillus after the 2020 reclassification, because it belongs to the emended genus of vertebrate-adapted species. Strain NCFM has been produced commercially since 1972 and its genome has been fully sequenced. La-5 is often combined with Bifidobacterium BB-12 in yogurts and capsules.

What the research says

Evidence is limited and depends on the strain and the condition. In antibiotic-associated diarrhoea, reductions were found for specific mixtures that include L. acidophilus (Bio-K+ with CL1285, and La5 with BB-12), not for L. acidophilus as a single ingredient. For children's acute diarrhoea, a meta-analysis of the LB strain found only limited evidence. For lactose intolerance, one industry-sponsored crossover trial of DDS-1 reported fewer symptoms, but an older strain (BG2FO4) did not help, and a systematic review found that probiotics in general did not relieve lactose intolerance. Reported harms are rare: L. acidophilus appears among published cases of heart valve infection, and D-lactic acidosis has been reported with a probiotic product in a child with short bowel syndrome.

Evidence grade: Limited evidence.

What goes wrong

A narrative review of 82 published cases of Lactobacillus heart valve infection found L. acidophilus in 11 of them. (Source 1)

• Expert review, not systematic, Very low certainty.
• Size: 82 patients from 77 studies.
• Who: Published case reports of Lactobacillus endocarditis.
• How long: Case reports up to September 2023.
• Result: L. acidophilus in 13.4% (11 of 82 patients). The review counts species in published cases and does not say which cases came from supplements.
• Funding: not stated in the passage we fetched.

Limit of this finding: A review that pooled 82 published case reports. It shows the infection happens, not how often.

The isolated species from the 82 patients with IE were L. rhamnosus in 23.2% (19 patients), L. casei in 13.4% (11), L. jensenii in 13.4% (11), L. acidophilus in 13.4% (11)

A case report describes D-lactic acidosis with brain symptoms in a 5-year-old with short bowel syndrome after a double dose of a probiotic product (Lactomin); the abstract does not name the species in the product. (Source 2)

• Case report, Very low certainty.
• Size: 1 child.
• Who: Child with short bowel syndrome.
• How long: 2 weeks of probiotic before symptoms.
• Result: Plasma D-lactate 5.537 mmol/l.
• Funding: not stated in the passage we fetched.

The probiotics the patient had taken were likely the cause of D-lactic acidosis and should therefore be avoided in patients with short bowel syndrome.

What the evidence supports

A systematic review of 228 trials found strain-specific efficacy for preventing adult antibiotic-associated diarrhoea for a few Lactobacillus products, one of them the Bio-K+ mixture containing L. acidophilus CL1285; the review states that other Lactobacillus strains did not show efficacy. (Source 3)

• Systematic review, Certainty not rated.
• Size: 228 trials overall.
• Who: Adults taking antibiotics (for this indication)
• How long: Varied.
• Result: Bio-K+ mixture: RR 0.56 (95% CI 0.40-0.79) from three trials with four intervention arms; L. acidophilus La5 + B. lactis Bb12: RR 0.67 (95% CI 0.47-0.94) from six RCTs in adults (figures from the full text; not in the quoted abstract).
• Funding: not stated in the passage we fetched.

Strain-specific efficacy for preventing adult antibiotic-associated diarrhea was clearly demonstrated within the Lactobacillus species [e.g., by the mixture of Lactobacillus acidophilus CL1285, Lactobacillus casei LBC80R, and Lactobacillus rhamnosus CLR2 (Bio-K+®), by L. casei DN114001 (Actimel®) and by Lactobacillus reuteri 55730], while other Lactobacillus strains did not show efficacy.

An industry-sponsored crossover trial reported that L. acidophilus DDS-1 reduced abdominal symptoms during a lactose challenge compared with placebo. (Source 4)

• Randomized trial, Low certainty.
• Size: not given in the passage we fetched.
• Who: Healthy volunteers aged 18 to 75 who complained of lactose intolerance.
• How long: 4 weeks per crossover arm, 2-week washout.
• Result: Diarrhoea p = 0.033, cramping p = 0.012, vomiting p = 0.0002, overall symptom score p = 0.037; no adverse events reported.
• Funding: industry-funded (sponsored by Nebraska Cultures, Inc., the strain's manufacturer)

demonstrated statistically significant reductions in abdominal symptom scores during the 6-h Lactose Challenge at week 4 for diarrhea (p = 0.033), abdominal cramping (p = 0.012), vomiting (p = 0.0002), and overall symptom score (p = 0.037). No adverse events were reported.

What the evidence does not support

In a small uncontrolled study, seven days of L. acidophilus BG2FO4 did not change breath hydrogen or symptoms in people with lactose maldigestion compared with their own baseline. (Source 5)

• Case series, Very low certainty.
• Size: 18 lactose maldigesters.
• Who: Adults with self-reported lactose intolerance and confirmed maldigestion.
• How long: 7 days.
• Result: Hydrogen production and symptom scores not significantly different from baseline; the randomisation was to omeprazole or no omeprazole, and all participants received the bacterium (no placebo arm).
• Funding: not stated in the passage we fetched.

Limit of this finding: This was a small single-group study with no placebo group, filed as the nearest design the library recognises.

overall hydrogen production and symptom scores after ingestion of Lactobacillus acidophilus BG2FO4 were not significantly different from baseline values.

A systematic review concluded that probiotics in general did not relieve lactose intolerance in adults, while some specific strains may work. (Source 6)

• Systematic review, Certainty not rated.
• Size: not given in the passage we fetched.
• Who: Adults with lactose intolerance.
• How long: Varied.
• Result: No pooled effect given in the DARE record.
• Funding: not stated in the passage we fetched.

Probiotic supplementation in general did not alleviate the symptoms and signs of lactose intolerance in adults in this review.

Where the evidence is mixed

A meta-analysis of four trials found that L. acidophilus LB shortened diarrhoea in hospitalised but not outpatient children, and concluded the evidence is limited. (Source 7)

• Meta-analysis, Low certainty.
• Size: 304 children in 4 RCTs.
• Who: Children aged 1-48 months with acute gastroenteritis.
• How long: Short courses.
• Result: Shorter diarrhoea in hospitalised children only; cure on day 3 similar, higher on day 4.
• Funding: not stated in the passage we fetched.

showed that Lactobacillus acidophilus LB (LB) reduced the duration of diarrhoea in hospitalised, but not outpatient, children compared with a placebo.

Where the research disagrees

Whether L. acidophilus relieves lactose intolerance

• Pakdaman et al. 2016 (sponsored by Nebraska Cultures), Crossover RCT, sponsored by the strain's manufacturer: "this unique DDS-1 strain of Lactobacillus acidophilus, manufactured by Nebraska Cultures, is safe to consume and improves abdominal symptom scores compared to placebo" (Source 8)
• Levri et al. 2005, Systematic review: "Probiotic supplementation in general did not alleviate the symptoms and signs of lactose intolerance in adults in this review." (Source 6)

Whether retail probiotic products contain what the label says

• Patro et al. 2016 (US FDA laboratory study of US products), Whole-genome sequencing survey of commercial products: "Overall, the products we tested adhered to the ingredient claims and lot-to-lot differences were minimal." (Source 9)
• Mazzantini et al. 2021 (review of product-quality studies worldwide), Narrative review: "Many reports indicated that the content of several probiotic formulations does not always correspond to the label claims in terms of microbial identification, number of living organisms, and purity" (Source 10)

How much

• Reference intake: No RDA, AI or other reference intake exists for L. acidophilus or any probiotic organism. The NIH Office of Dietary Supplements describes product amounts in CFU. (Source 11)
• Upper limit: No tolerable upper intake level has been set for any probiotic organism. (Source 11)
• Studied: Lactose trial (Saltzman 1999): L. acidophilus BG2FO4 twice per day for 7 days. (Source 12)
• Studied: Lactose trial (Pakdaman 2016): L. acidophilus DDS-1 or maltodextrin placebo once daily for 4 weeks in each arm of a 2-arm crossover, with a 2-week washout. (Source 13)

A common belief, and what the research shows

The belief: Acidophilus in yogurt or capsules helps any kind of diarrhoea.

What the research shows: The benefits found were specific to particular strains or mixtures and to particular kinds of diarrhoea. For children's acute diarrhoea with strain LB, reviewers concluded: "There is limited evidence to recommend LB for treating paediatric diarrhoea." A broader review warned that "Reviews and meta-analyses often pool together different types of probiotics, resulting in misleading conclusions of efficacy."

Questions and answers

What is it?

Lactobacillus acidophilus is a bacterium used as a probiotic. Strain NCFM has been produced commercially since 1972. Its complete genome, 1,993,564 nucleotides long and without plasmids, has been sequenced. (Source 14)

What does it do in the body?

Analysis of the NCFM genome identified several mucus- and fibronectin-binding proteins thought to be involved in attaching to human intestinal cells. That is a prediction from the genome, not an effect shown in people. Results from human trials are set out in the findings. (Source 15)

Is it good or bad for you?

Lactobacillus bacteria can, rarely, cause heart valve infection (infective endocarditis). In a narrative review of 82 published cases, L. acidophilus was the species found in 11 (13.4%). The evidence on benefits and other harms is set out in the findings. (Source 1)

How do you get more of it?

Studies gave it as capsules or in fermented dairy products, such as yogurt containing La-5. A mouse study found that the yogurt carrier changed how much benefit La-5 with BB-12 gave, so the form it comes in may matter. That is an animal result. (Source 16)

If it is harmful, what reduces it?

This usually does not apply. In one case report, a child with short bowel syndrome developed D-lactic acidosis after taking a probiotic product (Lactomin, whose species the abstract does not name); the product was stopped and she was treated with sodium bicarbonate and oral antibiotics. The authors concluded the probiotic was the likely cause and that probiotics should be avoided in short bowel syndrome. (Source 2)

Why might someone be low in it or missing it?

The literature we searched does not describe an L. acidophilus deficiency or explain why someone might be low in it. (Source 17)

We searched: Web searches for L. acidophilus deficiency, low levels and loss; reviews of probiotics in healthy adults (Khalesi 2019) and strain-specificity (McFarland 2018). None describes a deficiency state or its causes.

Which whole foods contain it or feed it?

Fermented dairy foods, such as yogurts and fermented milks labelled with added cultures, are the usual food source. A study comparing capsules with yogurt found that the carrier changed some effects in mice. (Source 18)

What happens if you do not have it?

No study we found shows harm from not carrying L. acidophilus. (Source 17)

We searched: Web searches for L. acidophilus deficiency or absence and health outcomes; reviews of probiotics in healthy adults (Khalesi 2019) and strain-specificity (McFarland 2018). None describes a deficiency state.

How can you test for it?

Consumer stool tests can report lactobacilli, but a 2026 evaluation of direct-to-consumer gut microbiome testing services found major differences between them, which the authors attributed to methodological variability and lack of sufficient quality control. (Source 19)

References

1. Antibiotics (MDPI). Infective Endocarditis by Lactobacillus Species—A Narrative Review. 2024. DOI 10.3390/antibiotics13010053. Read the source
2. Brain and Development. A case of D-lactic acid encephalopathy associated with use of probiotics. 2010. PMID 19917522. Read the source
3. Frontiers in Medicine. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. 2018. DOI 10.3389/fmed.2018.00124. Read the source
4. Nutrition Journal. The effects of the DDS-1 strain of lactobacillus on symptomatic relief for lactose intolerance - a randomized, double-blind, placebo-controlled, crossover clinical trial. 2016. PMID 27207411, DOI 10.1186/s12937-016-0172-y. Read the source
5. American Journal of Clinical Nutrition. A randomized trial of Lactobacillus acidophilus BG2FO4 to treat lactose intolerance. 1999. PMID 9925136. Read the source
6. Journal of Family Practice (via NCBI Bookshelf DARE). Do probiotics reduce adult lactose intolerance: a systematic review (DARE record). 2005. Read the source
7. Acta Paediatrica (via NCBI Bookshelf DARE). Meta-analysis shows limited evidence for using Lactobacillus acidophilus LB to treat acute gastroenteritis in children (DARE record). 2014. PMID 24175943, DOI 10.1111/apa.12487. Read the source
8. Nutrition Journal. The effects of the DDS-1 strain of lactobacillus on symptomatic relief for lactose intolerance - a randomized, double-blind, placebo-controlled, crossover clinical trial. 2016. PMID 27207411, DOI 10.1186/s12937-016-0172-y. Read the source
9. mSphere. Culture-Independent Metagenomic Surveillance of Commercially Available Probiotics with High-Throughput Next-Generation Sequencing. 2016. DOI 10.1128/mSphere.00057-16. Read the source
10. Frontiers in Microbiology. Spotlight on the Compositional Quality of Probiotic Formulations Marketed Worldwide. 2021. DOI 10.3389/fmicb.2021.693973. Read the source
11. NIH Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals. 2025. Read the source
12. American Journal of Clinical Nutrition. A randomized trial of Lactobacillus acidophilus BG2FO4 to treat lactose intolerance. 1999. PMID 9925136. Read the source
13. Nutrition Journal. The effects of the DDS-1 strain of lactobacillus on symptomatic relief for lactose intolerance - a randomized, double-blind, placebo-controlled, crossover clinical trial. 2016. PMID 27207411, DOI 10.1186/s12937-016-0172-y. Read the source
14. Proceedings of the National Academy of Sciences. Complete genome sequence of the probiotic lactic acid bacterium Lactobacillus acidophilus NCFM. 2005. PMID 15671160, DOI 10.1073/pnas.0409188102. Read the source
15. Proceedings of the National Academy of Sciences. Complete genome sequence of the probiotic lactic acid bacterium Lactobacillus acidophilus NCFM. 2005. PMID 15671160, DOI 10.1073/pnas.0409188102. Read the source
16. Probiotics and Antimicrobial Proteins. The Administration Matrix Modifies the Beneficial Properties of a Probiotic Mix of Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus acidophilus LA-5. 2021. DOI 10.1007/s12602-020-09702-2. Read the source
17. European Journal of Clinical Nutrition. A review of probiotic supplementation in healthy adults: helpful or hype?. 2019. PMID 29581563, DOI 10.1038/s41430-018-0135-9. Read the source
18. Probiotics and Antimicrobial Proteins. The Administration Matrix Modifies the Beneficial Properties of a Probiotic Mix of Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus acidophilus LA-5. 2021. DOI 10.1007/s12602-020-09702-2. Read the source
19. Communications Biology. Evaluating the analytical performance of direct-to-consumer gut microbiome testing services. 2026. DOI 10.1038/s42003-025-09301-3. Read the source