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When yogurt is frozen, is it as nutritious as regular yogurt? I know that acidophilus is an important ingredient in regular yogurt, so what happens to this live culture when the yogurt is frozen?

"Yogurt can be an excellent food choice," says Roberta Durschlag, SAR clinical assistant professor and director of nutrition programs. "It provides high-quality protein and is a very good source of calcium. There are, however, many varieties of yogurt available to the consumer, and they differ considerably in their content of fat and sugar.

"Yogurt prepared from whole milk contains approximately eight grams of fat per cup, versus three grams for yogurt prepared from low-fat milk and zero grams for yogurt prepared from nonfat milk. Furthermore, flavored yogurts contain considerably more sugar than plain yogurt. You can check the nutrient content of the yogurt you choose by reading the nutrition facts panel on the container.

"There has been considerable interest in the health benefits of the live bacteria added to milk in the process of producing yogurt. In the United States, two bacteria are required in the production of yogurt: lactobacillus bulgaricus and streptococcus thermopholis. Other bacteria may be added as well. Preliminary research has supported some of the health benefit claims, although more work is needed to confirm these findings.

"Consumers should be aware that not all yogurts contain live cells of these potentially beneficial bacteria. Although the federal government requires certain bacteria to be used in the production of yogurt, it does not require that the bacteria be live when the product is sold. Some manufacturers, in fact, heat-treat the product after incubation with the bacteria and thus kill the bacteria. To aid the consumer, the National Yogurt Association sponsors a voluntary labeling program. If a product contains at least 100 million live cells per gram when it leaves a manufacturing facility, it can display the Live and Active Cultures seal.

"Frozen yogurt is prepared by culturing a mix of milk, sweeteners, and emulsifiers and then freezing it. The nutrient content of frozen yogurt varies just as that of yogurt does. Thus, frozen yogurt prepared from whole milk will be higher in fat than that prepared from nonfat milk. The sugar content is usually high, unless artificial sweeteners are used, and will depend upon the amount added in manufacturing.

"According to Robert Garfield of the National Yogurt Association, there are no federal standards that govern the manufacture of frozen yogurt. Although the flash-freezing technique used in the production of frozen yogurt, unlike slow freezing in a freezer, should not kill the live cultures, there's no guarantee that this won't occur. Further, as with regular yogurt, some manufacturers heat-treat the product after incubation with bacteria, killing the bacteria. The National Yogurt Association also sponsors a voluntary labeling program for frozen yogurt; you can look for the Live and Active Cultures seal on containers of frozen yogurt."

23 April 2001
Boston University
Office of University Relations