Bifidobacterium longum Benefits: What It Does for Your Gut at Every Age

Bifidobacterium longum benefits your gut by breaking down carbohydrates your own body cannot digest, from the sugars in breast milk to the fibres in plants, and turning them into acids that other gut bacteria use. It is one of the first bacteria to settle in a baby's gut and one of the bifidobacteria most adults still carry decades later. Before picking up a probiotic with B. longum or B. infantis on its label, it helps to know which form is which, what the studies on each tested, and what a capsule can add to the B. longum already in your gut.

What is Bifidobacterium longum?

Bifidobacterium longum is a species of gut bacteria found in most people at every stage of life. In a study of 441 healthy Japanese people aged from newborn to 104, the B. longum group was found in 88% of them, the highest rate of any bifidobacterium, and at every age.1 Other bifidobacteria rise and fall with age. B. breve was found in about 70% of children under three, while B. adolescentis became common after weaning.1 In AMILI's own library of about 13,000 sequenced gut samples from people living in Asia, B. longum is the fifth most abundant species.

What does Bifidobacterium longum do in your gut?

Bifidobacterium longum breaks down carbohydrates that reach your large intestine undigested and turns them into acetate and lactate. Many of these carbohydrates pass through the small intestine intact because your own enzymes cannot split them, so they become food for bacteria in the colon.4

The acetate it makes feeds other bacteria. Species such as Faecalibacterium prausnitzii take up acetate and turn it into butyrate, a relay known as cross-feeding. Butyrate is the preferred fuel for the cells lining your colon and helps maintain the gut barrier,4 so much of what B. longum does for you depends on the other bacteria around it.

What is the difference between B. longum and B. infantis?

B. infantis is a form of B. longum, officially Bifidobacterium longum subsp. infantis, and it specialises in the sugars in breast milk. In 2008, scientists reclassified the former species B. longum, B. infantis and B. suis as three subspecies of one species.5 Two of them matter for people:

• B. longum subsp. infantis. Carries a large cluster of genes for taking in and digesting human milk oligosaccharides, complex sugars in breast milk that babies cannot digest themselves. It is adapted to the gut of breastfed infants.6
• B. longum subsp. longum. Adapted to carbohydrates from plants, and found in most people at every age, including adults.3

On a label, the subspecies and the strain code tell you which research applies. Much of the work on infantis is in breastfed babies. Labels do not always match current classification. The strain 35624, sold as B. infantis35624, was shown by genome sequencing in 2016 to be B. longum subsp. longum.7 Research on one strain does not transfer to another, even within the same subspecies.

What are the probiotic benefits of Bifidobacterium longum?

The probiotic benefits of Bifidobacterium longum in trials come from specific strains, and each finding applies to the strain, dose and people tested. The clearest examples:

• Breastfed babies. In a trial of 66 breastfed infants, those given B. infantis EVC001 for three weeks had more bifidobacteria, more acetate and lactate and a lower stool pH than babies given no probiotic. Babies with the most bifidobacteria also had about four times less endotoxin, an inflammatory fragment of other bacteria, in their stool. B. infantis levels stayed higher more than a month after supplements stopped.8 The trial had no placebo, and some of the researchers worked for the strain's manufacturer.
• Stress, sleep and memory in healthy adults. In a study of 22 healthy men, four weeks of B. longum1714 was linked to lower daily stress, a smaller rise in cortisol during a stress test and slightly better visual memory. The study was small and all male, and each man took a placebo for four weeks before the probiotic, so the order was not randomised.9 In a later randomised, double-blind trial of 89 adults with poor sleep, the main sleep score improved in both groups over eight weeks, but those taking 1714 reported better sleep quality and less daytime sleepiness at four weeks, and more energy at eight. Wrist-worn sleep trackers showed no difference.10 Researchers from the company that makes the strain were among the authors of both studies.
• Low mood alongside IBS. In a six-week trial of 44 adults with IBS and mild to moderate anxiety or depression, 64% of those taking 10 billion CFU of B. longum NCC3001 a day had lower depression scores, against 32% on placebo. Anxiety and gut symptoms did not change. Nestlé, which developed the strain, funded the trial.11
• IBS symptoms. In a four-week trial of 362 women with IBS, B. longum 35624 (sold as B. infantis35624) at 100 million CFU a day reduced abdominal pain and bloating more than placebo. A dose 100 times lower did not. The dose 100 times higher had problems with its formulation, so the trial cannot show whether more would have worked.12 In a later four-week trial of about 300 adults with bloating and discomfort but no IBS diagnosis, 1 billion CFU a day did not reduce average symptoms more than placebo, though it did give more bloating-free days. Both groups improved, which is common in gut symptom trials. Procter & Gamble, which sold the strain, ran this trial.13

These are four strains studied in specific groups of people. Evidence on B. longum from food is broader and less certain, because diet studies track the whole community of gut bacteria rather than one strain.

How do you increase Bifidobacterium longum naturally?

You can increase B. longum by feeding the population you already have, since most people pick it up early in life and what you eat afterwards decides how well it does. B. longum grows on fibres your body cannot digest, such as inulin, fructo-oligosaccharides (FOS) and arabinoxylan, found in foods like onions, garlic, bananas, oats and whole-grain bread.4 Adding one of these to a meal you already eat is an easy place to start, and our guide to bifidobacteria covers more ways to feed them.

Bifidobacteria are mainly gut bacteria, so where B. longum appears in yoghurt or fermented milk, it has usually been added by the producer. Many bifidobacteria are hard to keep alive in these foods through manufacturing and storage, so a label that names the strain and a live count is more useful than the word “bifidus”.14

Is Bifidobacterium longum safe?

For most healthy people, yes. B. longum is a normal resident of the gut from infancy, and bifidobacteria have a long history of use in food and supplements. Side effects in trials are usually mild and digestive, such as gas in the first days. Rare infections have been reported in people with weakened immunity or serious illness and in premature babies,15 so speak to a doctor before starting a probiotic if that applies to you or your baby, or if you take prescribed medication.

Does taking Bifidobacterium longum as a supplement work?

A Bifidobacterium longum supplement can add the species to your gut while you take it, and whether it stays depends mostly on the gut it lands in. Having B. longum in your gut and getting it there from a capsule are separate questions. A supplement has to clear three hurdles.

Surviving the product and the trip. Most bifidobacteria survive poorly in oxygen, so packaging and capsules that protect them from air and moisture help more of them arrive alive.

Reaching useful numbers. The adult trials above gave between 100 million and 10 billion CFU of a single strain a day. The dose that worked differs from strain to strain, so the dose tested matters as much as the strain.

Staying present. Most probiotic strains are found mainly while people take them and fade after they stop. This is because the bacteria already in your gut compete with newcomers for food and space, and together with your gut lining they limit which strains can settle, which researchers call colonisation resistance. In a placebo-controlled study, B. longum AH1206 stayed in the gut for at least six months in about 30% of the people who took it. Those people had started with little B. longum of their own and fewer of the genes it uses to digest certain carbohydrates, which suggests the strain filled an open niche, a role in the community that no resident already filled.16 A separate study found that how well probiotics settle in the gut lining can be predicted from each person's starting microbiome.17 A strain does not need to settle to have an effect, since it can still interact with your resident bacteria and gut lining as it passes through.