Like other top probiotics available today, LEAN’s 50-Billion Probiotic is packaged in a handy, delayed-release capsule, designed to protect non-acid-resistant bacteria until they reach deep into your GI tract, where they’re most needed. The result is maximum effectiveness – better gut health, an immune boost, and relief of common digestive problems.
Probiotics have also been researched for how they support the immune system. Studies suggest that probiotics can improve how the immune system functions such as by decreasing upper respiratory tract infections in adults and reducing the need for antibiotics. Studies in children show that a regular diet including probiotics reduces colds and flu-like symptoms and improves attendance in preschool and day care settings.
Unfortunately, the U.S. has no federal standards for probiotic supplements. Therefore, you run the risk of purchasing a product without any guarantee that it contains its advertised probiotic strains, that the strains are alive, or that the product is free from unhealthy ingredients. Therefore, it may be best to choose a brand-name probiotic that has research backing their effectiveness. Here are some examples:

Hi and thanks for reaching out! We recommend you to try Bio-K+ probiotics. To maintain a healthy intestinal flora: we recommend taking ¼ bottle of drinkable Bio-K+ or 1 Bio-K+ 12.5 Billion capsule per day. To improve intestinal flora health: we recommend taking ½ bottle of drinkable Bio-K+ product or 1 Bio-K+ 25 Billion capsule per day and to optimize intestinal flora health: we recommend taking 1 bottle of drinkable Bio-K+ or 1 Bio-K+ Billion capsule. Thanks!
While one 2009 study did show some evidence for reducing cold and flu symptoms in children ages three to five and a 2015 analysis showed probiotics to be better than placebo in preventing acute upper respiratory infections, neither were enough to convince the National Institutes of Health of the efficacy of probiotics for colds and flu. The NIH confirms, “the evidence is weak and the results have limitations.”
Ultimate Flora tested significantly higher than the majority of general probiotic blends. Critical Care is composed of very well-documented probiotic strains and is an effective addition to any lifestyle, capable of conferring a wide variety of health benefits. The probiotic strains are not only diverse, they were also resilient to outside influences and, in many cases, were successful in establishing colonies within the digestive tracts of study participants.
We also found strains linked to five other health benefits like weight loss and lowering cholesterol. We feature options for those cases below, but they aren’t top picks because those use cases aren’t as heavily researched as immune health or IBS relief. Still, chances are any probiotic supplement is going to make some improvement to your digestive health, so don’t be afraid to experiment.
Since the bulk of your natural flora exists in your gut, it makes sense that this is the part of your body that feels it most when bacteria become imbalanced. Women, in particular, can experience all kinds of digestive problems, particularly during hormone fluctuations. These are just some of the digestive symptoms a high-quality probiotic can help reduce and even treat:
Our gut is home to over 500 bacterial species. These “visitors” form a bioreactor, which facilitates digestion, provides nutrients, and helps form the immune system. Some important nutrients made by this bioreactor include several B vitamins, vitamin K, folate, and some short-chain fatty acids. Up to 10% of an individual’s daily energy needs can be derived from the byproducts of the good bacteria in your gut.
The idea that consuming probiotics can boost the ability of already well-functioning native bacteria to promote general health is dubious for a couple of reasons. Manufacturers of probiotics often select specific bacterial strains for their products because they know how to grow them in large numbers, not because they are adapted to the human gut or known to improve health. The particular strains of Bifidobacterium or Lactobacillus that are typically found in many yogurts and pills may not be the same kind that can survive the highly acidic environment of the human stomach and from there colonize the gut.
After the antibiotics had cleared the way, the standard probiotics could easily colonize the gut of everyone in the second group, but to the team's surprise, this probiotic colonization prevented the host's normal microbiome and gut gene expression profile from returning to their normal state for months afterward. In contrast, the aFMT resulted in the third group's native gut microbiome and gene program returning to normal within days.
To factor strain-specific benefits into our efficacy score, we referenced the information in these guides. Products were rewarded for containing strains on these lists. Additionally, measured levels of each strain were compared to what is thought to be effective based on these guides, and scores were scaled accordingly. In cases where products did not list strain-specific amounts, or their listed strains were not included in these guides, total measured CFUs were compared to a general effectiveness threshold of 1 billion CFUs cited by research published in the American Journal of Clinical Nutrition11. 
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