As you might know, probiotic supplements provide beneficial bacteria (usually Lactobacillus or Bifidobacterium) that normally inhabit the human digestive tract. Most of these “friendly” bacteria occur naturally in cultured milk products such as yogurt containing active cultures or acidophilus milk as well as other fermented foods such as live (refrigerated) pickles, sauerkraut, kimchi and kefir.
Prebiotics are types of non-digestible fiber that feed and promote the growth of probiotic bacteria. Prebiotics are readily available from the diet – they’re found in such fruits and vegetables as asparagus, artichokes, bananas, garlic, legumes, onions, wheat, tomatoes, and soybeans.
I generally don’t recommend that the average person who eats a healthy diet take probiotic supplements except when prescribed antibiotics. These powerful medications wipe out intestinal bacteria indiscriminately, including those that help keep the digestive system functioning normally and may support general health. Start taking probiotic supplements twice a day with meals as soon as you begin a course of an antibiotic, and continue using them for a few days after you finish your prescription. Look for brands containing Bacillus coagulans (BC-30) or Lactobacillus GG in liquid or capsule form. The dose is one tablespoon of the liquid culture or one to two capsules with meals unless the label directs otherwise.
There are a few exceptions to this rule, For example, when there’s a family history of allergy or eczema, babies given probiotics in their first 6 months of life (and whose mothers took probiotics during the last trimester of pregnancy) are less prone to eczema. Children with autism can also benefit from probiotics, possibly because they decrease leakage of large molecules from the gut that can trigger immune reactions with effects on brain function.
When I travel in underdeveloped countries, I take a probiotic supplement to reduce the risk of traveler’s diarrhea. Unless the package or product insert directs otherwise, the dose is one tablespoon of the liquid culture or one to two capsules after meals. Always check the expiration date to help ensure that the bacteria these products contain are alive and in good condition and look for ones with “colony forming units” (CFUs) in the billions. Be sure to protect probiotic products from exposure to heat, moisture, and air.
If you’re getting sufficient fiber in your diet from fruits and vegetables, you don’t need a prebiotic supplement.
Andrew Weil, M.D.