January 30, 2011 2:00 AM

With cold and flu season upon us, it makes sense to do all we can to keep our immune system at its best. There are a number of action steps we can take to be healthy this winter.

These include getting adequate, high quality sleep, keeping up with regular exercise, lowering our stress level, eating a healthy diet, drinking enough fluids, reducing the risk of consuming/coming in contact with various microbes, and possibly consuming one or more sources of probiotics (helpful bacteria).

Did you know that our intestinal tract comes in contact with numerous toxins and foreign substances that it needs to defend against? the intestinal tract is actually the largest immune organ in the body. It is lined with a high percentage of immune system cells. It also gets assistance from some beneficial microbes that live there.

A healthy intestinal tract naturally contains more than 400 different microorganisms. They can generally be divided into “good” and “bad” microbes. Ideally, we should have a balance between the two. Unfortunately, this balance can lean more toward the “bad” when the person is under stress, is fatigued, has been exposed to antibiotic therapy, consumes excessive alcohol, consumes foods containing bacteria, or is an older adult. a diet high in sugar, fat, animal proteins, processed foods, alcohol — and low in fiber, fruit, vegetables, whole grains, beans, nuts, and seeds — also promotes the “bad” microbes.

Symptoms of this imbalance can include food sensitivities, intestinal problems, poor digestion, and frequent illness or infections. Besides affecting the microbe balance in the intestinal tract, low intake of the healthy plant-based foods mentioned above can also compromise the person’s natural immune system in general.

How do the beneficial bacteria help to protect the body? They compete with the more negative microbes for food and locations of attachment in the intestinal tract. They can also directly kill the “bad” bacteria and stimulate the immune system to better fight off foreigners.

Because the lifestyle habits of many Americans promote the “bad” microbes, there is increasing interest in the intake of probiotics to improve the balance — more toward the beneficial side.

Probiotics are active (meaning alive) microbes (found in some foods and supplements) that survive the acidity of the stomach, take up lodging in the intestinal tract, and promote health.

Another term you may hear is “prebiotic.” This refers to non-digestible substances that are the preferred food source of the probiotics and help them to multiply more quickly. They also generate by-products that can directly kill microbes and improve the uptake of some nutrients. Prebiotics can be consumed through many plant-based foods or supplements.

The intake of foods and beverages containing probiotics has been around for centuries in countries around the world with the goal of improved immune system function. In the United States, the retail market for probiotics/prebiotics was $15 billion in 2008. It is estimated to increase to $22 billion by 2013.

Since probiotics stimulate the body’s natural immune system, another benefit is that they can possibly reduce the need for antibiotics. Reduced use of antibiotics can help counter the increasing number of antibiotic-resistant microbes. Because probiotics may reduce the risk of illness, they can also be an inexpensive way to lower personal health care costs.

It is important to keep in mind, however, that there are no standard recommendations for probiotic intake. It appears that their benefits are strain, dose, and condition-specific. An example is Lactobacillus GG, which, in certain doses, can help reduce rash symptoms from food allergies in children and reduce the risk of C. difficile infection, but may not help other conditions the way a different species of Lactobacillus can. It also means that doses of 100 million CFUs (colony-forming units) may work for one condition but might need to be as high as 30 billion for another. Numerous studies are under way to establish more guidelines.

With a goal of boosting overall immune system health, a mix of Lactobacillus and Bifidobacteria cultures is probably a good choice. Studies using some strains of these bacteria have shown reduced risk and/or shorter duration of illness in both children and adults. They are also recommended to restore intestinal health during and after antibiotic use.

Be aware that probiotics are sensitive to temperature, time, exposure to air, and other factors that can lower the number of CFUs. Probiotic supplements should be purchased from reputable companies that guarantee an amount of live cultures “good through the end of shelf life,” not “at the time of manufacture.” Consumers should follow the manufacturer’s instruction for storage.

Besides supplements, probiotics can be consumed through fermented foods, fortified foods, and cultured dairy products (yogurt, buttermilk, kefir, etc.). Healthy food sources can also provide other important nutrients. When using food sources, keep in mind that the probiotics tend to die if heated above about 110 degrees.

For information, check out usprobiotics.org and consumerlab.com.

Pam Stuppy, MS, RD, CSSD, LD, is a registered, licensed dietitian with nutrition counseling offices in York, Maine, and Portsmouth. She is also the nutritionist for Phillips Exeter Academy and is teaching healthy cooking classes at Stonewall Kitchen. Visit pamstuppynutrition.com for some healthy recipe ideas.

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