Does Acidophilus Cause Weight Gain?

No pooled analysis of adult trials has found that acidophilus, or live cultures as a group, adds weight: across 25 randomised trials in 1,931 adults, weight was 0.59 kg lower on live cultures than on placebo.¹ The idea that acidophilus causes weight gain comes from a 2012 analysis that pooled 17 human trials with 51 farm-animal studies and 14 laboratory models, and the human trials since have found weight slightly lower or unchanged.⁴ This page sets out what acidophilus is, where the weight-gain idea came from, why the first weeks can feel heavier, and why a probiotic product can still add calories.

Evidence at a glance

• Pooled trials: 25 trials, 1,931 adults, weight 0.59 kg lower on live cultures than placebo (2015); 15 trials, 957 adults with overweight, 0.60 kg lower (2018); 10 trials, 633 adults, no difference (2026).^{1, 2, 3}
• The direct test: 53 women aged 19 to 33, a two-strain capsule including acidophilus or placebo, six weeks; no body measure changed.¹¹
• Where the worry came from: a 2012 analysis pooling 17 human trials with 65 animal studies, acidophilus standardised mean difference 0.15 towards gain across species.⁴
• Not tested: weight gain as a primary outcome in healthy adults; water retention.

Sources checked on 29 October 2026.

What is acidophilus?

Acidophilus, also known as Lactobacillus acidophilus, is a naturally occurring bacterium found in the mouth, intestine and vagina, grown in culture for supplements. It is one of the species most often used in live-culture products made for women's intimate health. Its trial record is mostly in mixtures with other species, and the firmest results are these:

• Bacterial vaginosis (BV) is treated by a GP or sexual health clinic with antibiotics, the NHS says.⁶ Live cultures were tested after that treatment, not instead of it: across ten randomised trials in 1,234 women, BV came back in 14.8% of those who took live cultures after antibiotics against 25.5% without them.⁵
• Colds and other upper respiratory infections: in a Cochrane review of 12 trials in 3,720 people, fewer of those taking live cultures had at least one episode (odds ratio 0.53), on low-quality evidence.⁷
• Diarrhoea during antibiotics: across 63 randomised trials in 11,811 people, live cultures taken with antibiotics were associated with less antibiotic-associated diarrhoea (relative risk 0.58).⁸
• Eczema in babies: in a pooled analysis of 29 trials, live cultures taken in late pregnancy (relative risk 0.71), while breastfeeding (0.57) or given to infants (0.80) were followed by less eczema, on low-certainty evidence; ask a GP or midwife before any supplement in pregnancy.⁹

The trials by outcome, the foods that contain it and the safety record are on what is an acidophilus good for?; the women's evidence is on what do probiotics do for women?

Do probiotics cause weight gain?

Pooled adult trials of live cultures as a group show slightly lower weight, not gain: across 25 randomised trials in 1,931 adults, weight was 0.59 kg lower on average than on placebo.¹ A 2018 analysis of 15 trials in 957 adults with overweight or obesity found weight 0.60 kg lower, an effect its authors call small.² The most recent, 10 trials in 633 adults with overweight or obesity, published in 2026, found no significant difference either way.³

The idea that acidophilus adds weight comes from a 2012 analysis that pooled 17 human trials with 51 farm-animal studies and 14 laboratory models. In it, Lactobacillus acidophilus was associated with weight gain in humans and animals (a standardised mean difference of 0.15), Lactobacillus fermentum and Lactobacillus ingluviei with gain in animals only, and Lactobacillus gasseri with lower weight in people with obesity and in animals.⁴ That analysis reported effect sizes rather than kilograms, and a PubMed search on 29 October 2026 found no later pooled analysis of adult trials in which live cultures significantly raised weight. In the trial that tested the question directly, 53 women aged 19 to 33 took a two-strain capsule or placebo for six weeks and no body measure changed in either group; one strain was a Lactobacillus acidophilus, and the authors note the result does not support weight-loss claims either.¹¹

Do probiotics make you gain weight at first?

Some people feel heavier in the first week or two; that is not fat. The early effect the trials record is gas: "abdominal cramping, nausea, fever, soft stools, flatulence, and taste disturbance" were the common events in the 2025 Cochrane count, in 10.9% of people on live cultures against 12.2% of controls.¹² No trial has recorded water retention on live cultures, and the one trial that measured body fat, waist and skinfolds over six weeks found none of them changed.¹¹ A bloated first fortnight settles in most people; if it has not within a few weeks, stop and see whether it goes. Can probiotics make you feel worse before better? covers the adjustment period.

Can BV cause weight gain?

No. The NHS lists the symptoms of bacterial vaginosis as an unusual discharge with a strong fishy smell and a change in its colour and consistency, and says half of women with it have no symptoms; weight is not among them.⁶ The live cultures tested after BV antibiotics were counted for recurrence, not weight.⁵ Weight gain alongside irregular periods, tiredness or hair growth on the face is a GP question in its own right. The BV evidence is in what causes BV.

Can probiotics cause bloating and weight gain?

Bloating, yes: it is a short-lived early effect that many people notice when they first add live cultures to their routine. As for weight gain, the pooled adult trials above found weight slightly lower or unchanged. There are, though, three reasons a probiotic product can still work against a weight goal or deliver less than expected.

1. Some probiotic drinks and foods contain a lot of sugar

Flavoured yoghurt-style drinks can carry several teaspoons of sugar a bottle, and the calories count whatever the cultures do. Check the sugar line on the label.

2. The count on the label is what matters

Live cultures have a shelf life. A good label states the species, the number of live organisms and the date that number is guaranteed to; storage in transit and at home affects how many survive, which is why that date matters more than the count at manufacture.

3. Choose a capsule made to reach the gut

Live cultures have to pass through stomach acid to reach the intestine, so look for a product that states how its capsule and strains are designed to do that. If you have an existing health condition or a weakened immune system, the NHS says to talk to a doctor before taking any probiotic supplement.¹⁰

What we don't know

• Whether any single species, acidophilus included, changes weight in adults; the 2012 signal has not been tested in a trial built for it.^{4, 11}
• What happens beyond 12 weeks; the pooled trials stop there.^{2, 3}
• Whether early bloating is more common with some species or doses; the pooled counts did not separate them.¹²

Frequently asked questions

Which strains of probiotics make you gain weight?

In the 2012 analysis above, Lactobacillus acidophilus was associated with weight gain in humans and animals, and two other species in animals only; the pooled adult trials since have found weight slightly lower or unchanged on live cultures.^{1, 2, 3, 4} Check the label to see which species a product contains.

Does Lactobacillus acidophilus help you lose weight?

Not in the evidence so far: in the 2012 analysis it was associated with weight gain, while Lactobacillus gasseri was associated with lower weight in people with obesity.⁴

Is probiotics good for weight loss?

The pooled trials found small differences: weight 0.59 and 0.60 kg lower than on placebo in two analyses, and no significant difference in the most recent.^{1, 2, 3} Diet and activity remain the basis of weight management.

Can acidophilus be taken instead of antibiotics for BV?

No. The NHS says BV "is usually treated with antibiotic tablets or gels or creams" from a GP or sexual health clinic.⁶ In every one of the ten trials that measured recurrence, the live cultures were taken after or alongside the antibiotic course.⁵

Sources

1. Zhang Q, et al. Effect of probiotics on body weight and body-mass index: a systematic review and meta-analysis of randomized, controlled trials. International Journal of Food Sciences and Nutrition, 2015. Pooled analysis of 25 randomised trials, 1,931 adults; funding not stated in the record. PubMed 27149163.
2. Borgeraas H, et al. Effects of probiotics on body weight, body mass index, fat mass and fat percentage in subjects with overweight or obesity. Obesity Reviews, 2018. Pooled analysis of 15 randomised trials, 957 adults, 3 to 12 weeks; non-commercial support. PubMed 29047207.
3. Ko J, et al. Effects of probiotics and synbiotics on body weight management in individuals with overweight or obesity. Physical Activity and Nutrition, 2026. Pooled analysis of 10 randomised trials, 633 adults, 8 to 12 weeks; no conflicts declared. PubMed 42438848.
4. Million M, et al. Comparative meta-analysis of the effect of Lactobacillus species on weight gain in humans and animals. Microbial Pathogenesis, 2012. Pooled analysis of 17 randomised trials in humans, 51 farm-animal studies and 14 laboratory models; non-commercial support. PubMed 22634320.
5. Chieng WK, et al. Probiotics, a promising therapy to reduce the recurrence of bacterial vaginosis in women? A systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition, 2022. Pooled analysis of 10 randomised trials, 1,234 women; recurrence 14.8% against 25.5%, relative risk 0.55; no conflicts declared. PubMed 36204368.
6. NHS. Bacterial vaginosis. Page last reviewed 19 June 2026. nhs.uk/conditions/bacterial-vaginosis.
7. Hao Q, et al. Probiotics and acute upper respiratory tract infections. Cochrane Database of Systematic Reviews, 2015. Cochrane review, 12 randomised trials pooled, 3,720 people; odds ratio 0.53 for at least one episode, low-quality evidence. PubMed 25927096.
8. Hempel S, et al. Probiotics for the prevention and treatment of antibiotic-associated diarrhea: a systematic review and meta-analysis. JAMA, 2012. Pooled analysis of 63 randomised trials, 11,811 people; relative risk 0.58; US public funding. PubMed 22570464.
9. Cuello-Garcia CA, et al. Probiotics for the prevention of allergy: a systematic review and meta-analysis of randomized controlled trials. Journal of Allergy and Clinical Immunology, 2015. Pooled analysis of 29 randomised trials; eczema relative risk 0.71 (pregnancy), 0.57 (breastfeeding), 0.80 (infants); low-certainty evidence. PubMed 26044853.
10. NHS. Probiotics. Page last reviewed 24 November 2022 (review overdue). nhs.uk/conditions/probiotics.
11. Czajeczny D, et al. Does probiotic supplementation aid weight loss? A randomized, single-blind, placebo-controlled study with Bifidobacterium lactis BS01 and Lactobacillus acidophilus LA02 supplementation. Eating and Weight Disorders, 2021. Randomised trial, 53 women enrolled, 38 completed, 6 weeks; no conflict of interest declared. PubMed 32797375.
12. Esmaeilinezhad Z, et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews, 2025. Cochrane review, 47 randomised trials, 15,260 people; adverse events from 37 trials, 11,911 people; authors declare no relevant interests. PubMed 40931979.

General information, not medical advice. Live cultures are a food supplement, not a treatment; antibiotics are the treatment for BV.

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