Probiotics: Health Benefits and Side Effects

Probiotics are live bacteria and yeast that are good for you, especially your digestive tract. These naturally occurring microorganisms are considered "good" in that they keep "bad" bacteria and fungus in check. They can even promote vaginal health by preventing the overgrowth of microbes that cause yeast infections and bacterial vaginosis.

Probiotics are found in yogurt and fermented foods but can also be purchased as dietary supplements, skin care products, and vaginal suppositories.

The most common types of probiotics sold in the United States are Lactobacillus and Bifidobacterium. The increasing popularity of these products has led to misconceptions about what they can and cannot do and whether they can deliver the promised results.

This article discusses probiotic benefits for digestive and reproductive health. It also details the side effects of probiotics.

Health Benefits of Probiotics

A lot of research has been devoted to evaluating the benefits of probiotics, most especially in the area of digestive health. While some of the results have been positive, other long-held health claims have been unsupported by research.

Here are some of the key findings from recent research:

Irritable Bowel Syndrome

The role of gut microflora in the development of irritable bowel syndrome (IBS) is well established. As such, the body of research into the potential for probiotics in helping alleviate symptoms of IBS continues to grow. Several studies have found that probiotics can have a positive effect on the severity of common IBS symptoms—including abdominal pain and diarrhea.

Although clinical research has been encouraging, it hasn't been enough to garner an official endorsement from most gastroenterologists. The AGA guidelines do not recommend the use of probiotics in children and adults with IBS except in the context of a clinical trial.

Antibiotic-Associated Diarrhea

Other studies have focused on whether probiotics can play a role in preventing diarrhea caused by antibiotic use. Since antibiotics can kill both "good" and "bad" bacteria, the hope has been that probiotic supplements could help restore the digestive flora back to its normal state.

A 2018 review of studies from China concluded that probiotics can reduce the risk of diarrhea by 50 to 60 percent if taken with antibiotics, particularly the probiotics Saccharomyces boulardii and Lactobacillus rhamnosus GG.

The AGA guidelines recommend certain probiotic strains for adults and children on antibiotic treatment or other probiotics for prevention of C difficile infection. Of note, the AGA tempers this recommendation by saying patients with severe illnesses, an aversion to the cost or a low concern for C difficile development can reasonably choose to not take antibiotics at all.

Vaginal Infections

The use of probiotics in treating common vaginal infections, like bacterial vaginosis and vaginal candidiasis (yeast infection), remains controversial with some studies showing benefits and others not.

Of the oral supplements reviewed, Lactobacillus acidophilus, Lactobacillus rhamnosus GR-1, and Lactobacillus fermentum RC-14 were considered the most beneficial.

By contrast, the oral or vaginal use of probiotics has not yielded positive results in treating yeast infections, according to a 2006 review in the Journal of Antimicrobial Chemotherapy.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which consists of ulcerative colitis and Crohn's disease, is characterized by persistent gastrointestinal symptoms, including abdominal pain, bloating, blood in stool, flatulence, diarrhea, nausea, and vomiting.

Interestingly, while much of the current evidence suggests that probiotics that may prevent recurrence of ulcerative colitis, the same was not seen with Crohn's disease. Moreover, the benefits were attributed to specific probiotic strains or combinations of strains.

By contrast, a 2009 Cochrane review, which evaluated 23 different randomized controlled studies, found that probiotics were no more effective in preventing or treating Crohn's disease than a placebo.

Possible Side Effects of Probiotics

Probiotic supplements are considered safe and well-tolerated if taken as directed. Side effects of probiotics may include bloating and gas. Taking a yeast-based probiotic can sometimes cause constipation or increased thirst. Most of these side effects are mild and tend to improve once your body adapts to treatment.

Probiotics may contain allergens that can affect people with an egg or soy allergy. People with a yeast allergy would need to avoid yeast-based probiotics.

There are no documented drug interactions associated with probiotic supplements. With that said, speak with your healthcare provider before taking a probiotic if you are on antibiotics or antifungal medications. Taking these together can negatively alter your digestive or vaginal flora.

Probiotic Dosage and Preparation

Because there are many different probiotic strains and formulations, there is no set dosage. Factors like age, weight, and general health may influence how much or little you need.

As a general rule, a probiotic should provide at least 1 billion colony forming units (CFU) per day, with dosages ranging from 1 billion to 10 billion for adults. If used in children, less than 1 billion CFU would be prescribed. Probiotic supplements are generally taken on a daily basis, ideally before a meal.

Probiotic suppositories tend to have higher CFUs as they are meant for short-term use only. Generally speaking, suppositories should be used for no more than seven consecutive days.

What to Look For

In the United States, probiotics are classified as dietary supplements. Under this classification, the products are not strictly regulated and are allowed to be sold without the burden of clinical research. With that being said, the U.S. Food and Drug Administration (FDA) forbids manufacturers making any claims that the products can cure, treat, or prevent any disease or health condition.

When used as a food ingredient, probiotics fall under the FDA umbrella category "GRAS," meaning they are "generally regarded as safe." 

Other Questions

Which foods are highest in probiotics?

Generally speaking, it is always best to get your daily nutrients for food. Even though probiotic supplements are unlikely to cause you any harm, you should consider trying the following if you've been advised to increase your probiotic intake:

• Kefir: 27.7 billion CFU per 1-cup serving
• Kimchi: 2.6 billion CFU per 1/2-cup serving
• Yogurt: 3.6 billion CFU per 1-cup serving
• Miso: 54.1 thousand CFU per tablespoon
• Sauerkraut: 195.2 million CFU per 1/2-cup serving
• Kombucha: 23.1 million CFU per 1-cup serving