By Susan M. Kleiner, PhD, RD, FACN, CNS
If you eat yogurt, consider yourself cultured. A food made of milk fermented by bacterial cultures, yogurt has been eaten throughout the world for at least 4,000 years. Asians, Middle Easterners, Europeans and Scandinavians all have their own names for this time-honored dietary staple. In certain languages the word for yogurt means “life”— the ancient Assyrian lebeny and the Middle Eastern laban— reflecting a strong belief in its life-giving properties. Today scientists are actively investigating the many possible health benefits of yogurt through its contribution to good nutrition, as well as its potential for preventing and treating certain diseases and helping with body weight control.
What is Yogurt?
Yogurt starts out as pasteurized milk. Then two strains of beneficial bacteria, Lactobacillus bulgaricus and Streptococcus thermaophilus are added that ferment and transform the milk, not unlike the process that’s used to make beer, wine or cheese. Only the bacterial cultures are different. Some yogurt products contain a third bacterial culture, L. acidophilus, which is added at the same time as the other cultures. It is the fermentation process carried out by the bacterial cultures that creates yogurt, with its unique taste, texture and healthful attributes.
Although there are numerous nutritional benefits attributed to the milk properties of yogurt (discussed below), the bacterial cultures themselves carry a significant health benefit. The word “probiotic” means “for life” in Greek and it has been chosen by scientists as the best term to describe these beneficial colonies of bacteria. Simply put, the definition of a probiotic is a live microbial food ingredient that is beneficial to health. By this definition, a probiotic must contain a “live” microbe.
Some yogurt products are heat-treated after fermentation, which kills most of the beneficial active cultures. So that consumers can identify those yogurt products that contain live and active cultures, the National Yogurt Association (NYA) has established a special “Live & Active Cultures” seal. This voluntary seal is the industry validation that those products contain at least 100 million live cultures per gram at the time of manufacture, and that the cultures have the ability to ferment milk into yogurt. A probiotic supplement should also indicate an expiration date.
In certain central Asian societies where yogurt has been eaten for centuries, many people reportedly live to be 100 years of age or older. Their long lives are often attributed to the fact that they consume yogurt on a regular basis. (Today, it’s believed that most of these venerable elders exaggerated their ages). The finding that the live, active cultures in yogurt can survive digestion in the stomach and pass into the small intestine and the colon intact has led scientists to investigate the age-old notions about this food’s reputed and potential health benefits.
- Balance Intestinal Flora. We all have bacteria in our guts. In fact, over 500 species of bacteria occur in the human gastrointestinal (GI) tract and account for about 95 percent of the total number of cells in the human body! Many of the normal GI bacteria are probiotic bacteria that belong to the same families as the commercial probiotics used in yogurt production. One of the proposed benefits of probiotics is that they can bring the gut flora into a healthier balance, minimizing the levels of pathogenic bacteria that can survive there.
- Relieve Diarrhea. Even though there are various causes of diarrhea, the overall evidence for the prevention and treatment of a variety of types of diarrhea with probiotics is promising. Probiotics are especially effective in treating antibiotic-induced diarrhea and common diarrheas of childhood and infancy. They are less effective in preventing traveler’s diarrhea.
- Relieve Symptoms of Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD). Probiotics may play a role in relieving symptoms of IBS. After 12 months of a double-blind, placebo controlled trial with Lactobacillus plantarum culture, the treated patients had reduced symptoms and had better overall GI function than the control group. The benefit is only maintained with regular probiotic administration.
IBD refers to Crohn’s disease and ulcerative colitis. The use of probiotics for the treatment and postoperative maintenance of Crohn’s disease and for the inflammation of ulcerative colitis is encouraging. Human and laboratory research has shown positive effects on symptoms and immune responses.
- Relieve Symptoms of Lactose Intolerance. Probiotic products that contain lactobacilli or bifidobacteria can reduce, although not totally eliminate, lactose intolerance. The research suggests that probiotics both increase lactose digestion and delay the transit of food from the stomach to the small intestine, allowing for better digestion.
- Possibly Prevent Colon Cancer. There are a number of places in the cascade of events that lead to cancer where probiotics show a beneficial influence. These include:
- Enhancing immune function
- Degrading cancer-causing chemicals
- Altering the total numbers and activity of intestinal flora
- Producing anti-cancer compounds in the colon
- Altering the metabolism of intestinal flora
- Altering the physiological and biochemical environment of the colon
- Influencing the physiology of the host
The probiotics lactobacilli, bifidobacteri, and Streptococcus thermophilus have been shown in laboratory studies to prevent gene mutation and may prevent the mutation step that leads to cancer.
- Enhance Immune Function. Probiotics can prevent the passage of disease-causing bacteria across the barrier of the intestinal wall. They can also compete with them in the GI tract. Probiotics can enhance the activity of the white blood cells (leukocytes) of the immune system, stimulate immune resistance to pathogenic bacteria and enhance the production of immune compounds, increasing the intestinal immunologic barrier.
- Inhibit the Stomach Ulcer Microbe. Several strains of lactobacillus can inhibit or kill Helicobacter pylori, the microbe that causes stomach ulcers. When taken along with antibiotics for the eradication of H. pylori, lactobacilli were effective in reducing medication side effects such as diarrhea, altered taste and nausea.
Other Health Benefits of Yogurt
All dairy foods are excellent sources of protein, calcium, phosphorus, magnesium, riboflavin, vitamin B12 and niacin. Yogurt, however, is a unique source of nutrients and could be considered superior to milk in several important respects. For example, because yogurt is more concentrated than milk, a single cup of yogurt serves up 30 to 45 percent of the RDA for calcium. Thus, yogurt provides 25 to 50 percent more calcium than an equal amount of milk. Moreover, the specific combination of nutrients in yogurt actually enhances the intestinal absorption of many of the other minerals, such as phosphorus and iron, and because yogurt is often fortified with non-fat milk solids, it may contain more protein than milk.
The culturing, or growing of the bacteria that make yogurt, also affects the nutrient content. As part of their metabolic process, the yogurt cultures produce folic acid, giving yogurt a folic acid content that is nearly twice that of milk. On the other hand, the culturing process uses up vitamin B12, so there is less of this vitamin in yogurt than in milk.
Protein. Protein is essential for maintaining and repairing the body’s tissues; for the optimal functioning of the immune system; for healthy growth during pregnancy, infancy, childhood, and adolescence; and for muscle building in adults. Both milk and yogurt are good sources of protein, but because of the unique culturing process that creates yogurt, the protein in yogurt is more easily digested than that in milk. While this does not make a great deal of difference for adults, it can make the transition from breast milk or formula to dairy products easier for infants and young children, and for people recovering from diarrhea and intestinal disorders.
As mentioned above, non-fat milk solids are added to many low-fat and non-fat yogurts to give them a thick, custardy consistency. This processing technique offers the added benefit of raising the protein content of these yogurts, as well as enhancing the content of minerals and vitamins.
Calcium. Ninety-nine percent of the body’s calcium is stored in the bones and teeth. The skeleton is continuously undergoing a remodeling process in which it loses and gains bone minerals throughout life. When bone loss is much greater than gain, the bones can become brittle and weak and more susceptible to fracture— a condition well-known as osteoporosis. An adequate amount of calcium in the diet throughout a lifetime is an important step in preventing osteoporosis, and yogurt is an excellent source of calcium. Depending on the type of the yogurt, products contain anywhere from 200 to 488 milligrams of calcium in one cup.
Lactose. Lactose, the natural sugar found in milk, enhances intestinal absorption of calcium. When digested, lactose is broken down into two simple components, glucose and galactose. But in order for lactose to be reduced to its smaller parts, the enzyme lactase is required. Unfortunately, many people lack this enzyme in their digestive tracts. This condition, called lactose intolerance, causes gastrointestinal upset when a food containing lactose is eaten. People with lactose intolerance tend to avoid milk products, losing the nutritional advantage that comes from dairy products.
Cultured yogurt offers a solution. The live, active cultures produce their own lactase that predigests much of the lactose in yogurt, reducing the absorption problem. Additionally, the lactase-producing live cultures survive passage through the gut where they are able to help digest whatever lactose is left in the yogurt. Thus, cultured yogurt products allow mildly lactose intolerant people to enjoy all the benefits of milk without suffering the discomfort.
Yogurt and Body Weight
Research during the past few years has shed light on the influence that calcium has on body weight. Dr. Michael Zemel at the University of Tennessee has led much of the research into calcium and weight control. Through his work and that of others, it has been discovered that there is an obesity gene in human fat cells that is turned on and off by the presence or absence of calcium. When calcium levels are low, the gene is turned on and promotes fat production and energy storage. At the same time, the system that breaks down fat and burns energy is suppressed. When calcium levels are abundant, the obesity gene is turned off, fat production is decreased and breakdown of fat is increased, along with increasing thermogenesis, or calorie burning. Dr. Zemel calls this an “anti-obesity effect.”
But calcium isn’t the only thing that seems to be affecting fat loss and weight control. In most of the research studies done to date, subjects obtaining their calcium from milk and dairy products have had significantly greater weight control, less fat and more lean body mass compared to those who get their calcium predominantly from supplements.
Dr. Zemel did a study to examine the effects of adding yogurt instead of milk to the diet to see if there were similar weight loss benefits. Thirty-four obese adults were assigned to one of two reduced-calorie diet groups. Group one ate 1,100 milligrams of calcium a day including three servings of yogurt. Group two ate a low-calcium diet of only 500 milligrams a day and no yogurt. Both groups followed a diet with a 500-calorie daily deficit. After 12 weeks, those who ate the high-calcium yogurt diet lost 22 percent more weight and 60 percent more body fat than the control group. They also lost 80 percent more abdominal fat.
Supplements vs. Food
Why bother eating yogurt for your probiotics when you can just pop a pill? In addition to losing the awesome nutritional benefits and great taste from the yogurt, scientists are still not certain that the probiotics are the only important components in yogurt that exert stimulatory effects and modifications on the immune system. This area is still not completely understood. Although the presence of the bacterial culture is thought to be essential for yogurt to exert its beneficial effects, other nonbacterial components of yogurt, such as whey protein, short peptides and conjugated linoleic acids, are believed to contribute important properties, as well.
Low-fat and non-fat: There are three types of yogurt: regular, low-fat and non-fat yogurt. Yogurt made from whole milk has at least 3.25 percent milk fat. Low-fat yogurt is made from low-fat milk or part-skim milk and has between two and 0.5 percent milk fat. Non-fat yogurt is made from skim milk and contains less than 0.5 percent milk fat.
Lite (light) yogurt: 1/3 less calories, or 50 percent reduction in fat, than regular yogurt.
Swiss or custard: Fruit and yogurt are mixed together for individual servings. To ensure firmness or body, a stabilizer like gelatin may be added. These products are also referred to as “blended” yogurt.
Contains active yogurt cultures: Yogurt labeled with this phrase contains the live and active bacteria thought to provide yogurt with its many desirable healthful properties. Look for the NYA Live & Active Cultures seal to ensure that the yogurt you buy contains a significant amount of live and active cultures.
Heat-treated: Yogurt labeled with this phrase has been heated after culturing, thereby killing the beneficial bacterial cultures.
Liquid or drinkable yogurt: Fruit and yogurt are blended into a drinkable liquid.
Made with active cultures: FDA regulations require that all yogurts be made with active cultures. Only those that are not heat-treated, however, retain live and active cultures when they reach consumers.
Sundae or fruit-on-the-bottom: Fruit is on the bottom, so that turned upside down, it looks like a sundae. Consumers can mix the fruit and yogurt together to make it smooth and creamy.
Source: AboutYogurt.com, official website of the National Yogurt Association
A CALCIUM COUNTER’S GUIDE
The RDA for calcium for adults aged 19-50 is 1,000 milligrams (mg) per day and 1,200 mg per day for adults older than 50.
|1% fat cottage cheese, 1 cup||138 mg calcium|
|American cheese, 1 oz.||174 mg calcium|
|fat-free milk, 1 cup (8 oz.)||223 mg calcium|
|Parmesan cheese, 1 oz.||336 mg calcium|
|part-skim milk ricotta cheese, 4 oz.||337 mg calcium|
|fat-free plain yogurt||488 mg calcium|