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A. Judith C. Thalheimer, RD, LDN, managing editor of Tufts Health & Nutrition Letter, answers: “Yogurt is made by fermenting milk. The fermentation process breaks down much of the lactose—the sugar naturally found in milk—into its constituents, glucose and galactose. For this reason, many people who suffer from lactose intolerance (low levels of the lactase enzyme necessary to break down lactose) find they can tolerate some yogurt. Some styles of yogurt, like Greek and Icelandic (skyr) are strained. This makes them thicker and more protein-rich than other yogurts. Straining also removes some lactose, so these yogurts may be even better tolerated.
“Live active cultures are probiotics that help maintain a healthy gut microbiome. Bacteria commonly used in yogurt, Lactobacillus bulgaricus and Streptococcus thermophilus produce their own lactase enzyme, and it has been suggested that consuming these live bacteria may help with lactose digestion.
“Some yogurt products are heat treated after fermentation. This kills most of the bacteria responsible for breaking down the milk sugars, and likely destroys any lactase enzyme they have released into the yogurt. Three small studies conducted in the early 2000s found that, while heat treated fermented milk was better tolerated by individuals with lactose intolerance than regular milk, yogurt with live cultures resulted in less severe gastrointestinal symptoms and lower breath hydrogen excretion (a test for lactose intolerance).
“If you have lactose intolerance, yogurt may still be an option for you. It is possible that yogurts with live and active cultures may have a slight edge over heat-treated products (the label will indicate if live cultures are present). Be aware that the number of live bacteria in a container of yogurt will dwindle over time. For general health, choose products with little or no added sugars, and mix in your own fresh or frozen fruit.”