One of the most nutritious and healthful foods on supermarket shelves is yogurt. I'm not talking about frozen yogurt; though a fine dessert, it has too little of the beneficial ingredients to qualify as a health-promoting food. Nor do I mean the heavily sweetened varieties, in which calories overwhelm nutrients, or heat-treated yogurts, in which beneficial micro-organisms are killed for the sake of a longer shelf-life.
I mean plain, unadulterated low-fat or nonfat yogurt, to which you can add fruit if you like, or which you can use as an ingredient or accompaniment to a variety of dishes, like homemade smoothies, soups, pancakes and curries. Yet another option is to prepare yogurt "cheese" by draining off the liquid whey portion to produce a thick, nutrient- packed, creamy product that is not at tart as yogurt and can be used in many dishes in place of fattier and less nourishing foods like cream cheese and sour cream. A new book by Nikki and David Goldbeck, "Eat Well the YoChee Way," provides hundreds of recipes for yogurt cheese, plus instructions for how to prepare this versatile food.
Eating Bacteria Is Good for You
Yogurt has been receiving an increasing amount of attention from health-oriented nutrition scientists because this food and the bacteria used to make it have been linked to a variety of potential health benefits, from protection against intestinal and vaginal infections and bowel cancer to increased calcium absorption and overall enhancement of the immune system.
The health and nutritive value of yogurt depends on how it is prepared. Basically, yogurt is fermented milk made by adding to cow's or soy milk bacteria that convert the sugar lactose into lactic acid, resulting in a creamy texture and tart taste. The bacteria most often used to prepare yogurts sold in the United States are Lactobacillus bulgaricus and Streptococcus thermophilus.
But other bacterial cultures that may offer further health benefits are used in some products. Some manufacturers add as many as four others to the two basic bacteria: Lactobacillus acidophilus, casei and reuteri and Bifidobacterium bifidum. All six of these organisms are known as probiotics because, when consumed live and in sufficient quantities, they benefit the consumer through their effects in the intestinal tract. These are the so-called good bacteria that help to keep illness-causing organisms under control, said Dr. Sherwood Gorbach and Dr. Barry Goldin of the Tufts University School of Medicine.
In addition, yogurt contains a so-called prebiotic, inulin, a nondigestible ingredient that enhances the growth and survival of health-promoting bacteria in the lower digestive tract. People taking antibiotics are often advised to eat yogurt to restore beneficial bacteria to the gut that the medicine may kill. Lactobacillus, among other probiotics, has been shown to be clinically effective in preventing antibiotic associated diarrhea, according to a review of the literature by Dr. Rial D. Rolfe, a microbiologist at Texas Tech Health Sciences Center.
To glean any benefits from yogurt bacteria, however, the product must contain live, active cultures; if the yogurt has been pasteurized by the manufacturer or heated at home, the bacteria are dead and cannot help the consumer beyond providing a lactose-reduced food for people who are lactose intolerant.
Many health claims have been made for the probiotic and prebiotic ingredients in yogurt, including the relief of constipation and diarrhea and a reduced risk of developing heart disease, diabetes, osteoporosis, obesity and colon cancer. At this point, such claims are at best tentative. What is required are long-term controlled clinical trials in which some participants regularly eat yogurt with active cultures and others eat a look-alike yogurt in which the cultures have been killed. These studies, however, are costly and unlikely to be done soon.
Meanwhile, here is what is known or suspected, based on preliminary evidence from studies in animals and small, short-term human trials. Active yogurt cultures can relieve diarrhea, particularly that caused by rotavirus in children and lactose intolerance. It may also help people taking antibiotics, and preliminary evidence in animals suggests that eating yogurt regularly may protect against colon cancer. Although prebiotics increase the absorption of calcium and magnesium, no studies have yet shown that regularly eating yogurt helps to prevent osteoporosis. However, regular consumption of yogurt with active cultures may counter vaginal yeast infections in some women.
More exciting, perhaps, are the potential benefits to the immune system. Dr. Simin Meydani, a nutrition researcher at Tufts, reviewed 161 published reports on the immunological effects of yogurt. She concluded that, in general, the results "support the notion that yogurt has immunostimulatory effects," and may be especially helpful for people with declining immune function, like the elderly, as well as those whose immune systems are compromised by disease or medical treatment.
"Putting the pieces of information together suggests that yogurt could have immunological benefits," Dr. Meydani said. There is some evidence, for example, that yogurt-induced immune enhancement is associated with a lowered incidence of conditions like cancer, gastrointestinal disorders and allergic symptoms. But, she added, most studies have been either poorly designed, too small or too short to draw firm conclusions.
No Question About Nutrition
"Yogurt is an excellent food regardless of its immune effects," Dr. Meydani said.
Most wholesome are the plain yogurts that are low in fat and free of added sugar. In comparing 8 ounces of plain, low-fat or nonfat yogurt with 8 ounces of milk, yogurt comes out ahead with more calcium (up to 450 milligrams, 100 more than milk), phosphorus, potassium and folic acid and other B vitamins for the same number of calories, about 90 to 110.
Yogurts made from whole milk naturally have more fat (about 7 grams per cup) and more calories (about 140) than nonfat yogurt (about 100 calories). Full-fat yogurt is recommended for babies and toddlers, who need the fat and cholesterol for brain development and overall growth, but after age 2 it is best to switch to lower-fat products.
Yogurt is also a good source of protein, with as many as 13 grams in a cup of nonfat products (skim milk has 8 to 10 grams). While there is more calcium in yogurt than milk, yogurt, unlike milk, is rarely fortified with vitamin D, which is essential to calcium absorption and use.
The Center for Science in the Public Interest, a Washington-based consumer organization, recently evaluated the nutritional characteristics of dozens of yogurt products in its monthly newsletter, Nutrition Action.
While sweetened yogurts were not all on the center's no-no list, those considered acceptable contained, per ounce, no more than 5 grams of sugar, 30 calories and one-quarter gram of saturated fat and at least 3 percent of a day's worth of calcium.
Among child-friendly yogurts, acceptable ratings went to Stonyfield Farm Yobaby and Yosqueeze and Dannon Danimals Drinkable Lowfat Yogurt. Other acceptable yogurt selections included Dannon Blended Nonfat, Horizon Organic Dairy Fat Free, plain and flavored; Stonyfield Farm Nonfat, plain and flavored; Dannon Fat Free, plain and some Dannon Lowfat flavors; Columbo Classic Lowfat lemon and vanilla; and Silk Cultured Soy Yogurt, plain and flavored.