Bifidobacteria, Lactobacillus... Should you trust the health claims for these microorganisms added to dairy products? Three leading specialists—gastroenterologist and Inserm researcher Marie-Christine Boutron, INRA microbiologist Gérard Corthier, and agri-food expert Fabiola Flex—separate fact from fiction on probiotics. Supermarket dairy aisles now resemble a farm visit, with probiotics—beneficial live microorganisms—everywhere.
These "friendly" bacteria (lactobacilli, bifidobacteria, Streptococcus thermophilus) and yeasts target harmful bacteria in the colon. However, their effects are temporary. "They don't adhere to the intestinal mucosa or multiply there," explains Dr. Marie-Christine Boutron, gastroenterologist and Inserm researcher. "They function for about 10 days after consumption, then disappear."
In plain yogurts, those enriched with bifidobacteria and lactobacilli (like B’A, Activia), mini-bottles of fermented milk (Actimel, Yakult), and more. All deliver probiotics.
Challenge: Stomach acids destroy most during digestion—classic yogurt delivers just 1% live microbes to the colon, while fortified products, with higher doses, deliver about 20%. They're also in over-the-counter supplements like Ultra-levure capsules and powders.
Video of the day:"Probiotics show preventive effects only against atopic eczema in children. No evidence supports benefits for adult or food allergies," cautions Gérard Corthier, head of INRA's "Physiology of the Digestive System, Microbiology, and Human Nutrition" unit.
"Bifidobacteria can ease abdominal pain, bloating, spasms, and general gut discomfort," says Dr. Boutron. Opt for products with the farthest expiration dates for maximum live probiotics. She recommends a weekly Ultra-levure course, especially for premenstrual syndrome-related issues.
"Test for two to three months—relief varies by individual gut flora, unique like fingerprints. For lactose intolerance causing bloating hours after milk, switch to yogurt; its bacteria aid digestion despite similar lactose levels," she adds.
"Claims of 'rebalancing' or 'regenerating' are misleading—we don't even know what a 'balanced' flora looks like," stresses Corthier. Probiotics may introduce absent beneficial bacteria (just 10% of total flora), but no definitive studies prove rebalancing. They can improve slow transit (three to four bifidobacteria yogurts daily) or combat traveler's diarrhea with Ultra-levure.
"Possibly, but not guaranteed," notes Corthier, as 70% of immune defenses reside in the gut. Actimel's Lactobacillus casei defensis earned French Afssa approval for "supports natural defenses."
Reality? "It slightly enhances defenses—if poor before, it improves marginally; if strong, no change," he says. Studies used two vials daily, not one as advertised. Check strains precisely (e.g., "defensis" for Actimel, "shirota" for Yakult)—generics differ. Patented strains aren't replicated.
"Experimental only—stay cautious," advises Dr. Boutron. Animal studies suggest yogurts protect against tumors via detoxifying enzymes (e.g., from charred meat). Human evidence is lacking, but daily yogurt is nutritionally sound.
University of Washington research on germ-free mice showed 42% less fat mass despite triple food intake, hinting certain bacteria promote fat storage. Human translation pending.
"Many uncertainties, few reliable products," warns Corthier. Test cautiously (max two daily)—high doses cause gas. Probiotics aren't essential for health.
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