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Foods that fight the flu

Debbie Petitpain | MUSC News Center | October 14, 2014

Foods for the flu
Sarah Pack

It’s that time of year again. The nights are cooler, the days are shorter, the mornings are crisp. It’s fall. And with it, comes cold and flu season. As people spend more time inside and in close quarters with others, it becomes easier to spread germs and disease. While there are no scientifically proven direct links between lifestyle and enhanced immune function, it is easy to fortify your defenses with some healthy food choices.

The immune system is made up of the innate system, which is nonspecific, always prepared and the body’s first line of defense, and the adaptive system which attacks specific antigens but only after being primed by an initial exposure (for example, by a vaccine) and at an extreme metabolic cost. These systems act both independently and cooperatively.

Research clearly supports that food has healing power and can both enhance immunity and aid in recovery although the complexity of the immune system has made it difficult for scientists to isolate the exact roles certain nutrients play in the immune response. Most likely, it a concerted effort between several macronutrients, vitamins, minerals and phytonutrients. Just the same, a healthy diet is a tasty way to take a daily dose of preventative medicine and there’s no harm in eating more of these specific foods during this cold and flu season.

Debbie Petitpain Nutrition 

1. Sauerkraut

Fermented foods like sauerkraut, yogurt, miso, kefir, kombucha tea, and kimchi keep the gut healthy and a healthy gut is the primary barrier for pathogens trying to enter the body through the digestive tract. In fact, the gut-associated lymphoid system (GALT) is the largest immunologically competent organ in the body.

The gut is populated with a complex of microorganisms referred to as the gut flora or microbiota. These “bugs” protect against pathogens through a variety of possible mechanisms, including inhibition of the growth of pathogens by competing for nutrition, limiting movement across the intestinal wall by competing for sites of absorption, and by producing antimicrobial metabolites and possibly acidifying the environment so “bad bugs” can’t thrive.

Your diet feeds you AND your gut microbiota and can be used to increase the ratio of the “good-for-you” bugs, referred to as probiotics, in the gastrointestinal tract. Fermented foods are tried and true sources of probiotics (just watch out for the added sugars in yogurt and kefir and the sodium content in sauerkraut and kimchi). Friendly bacteria also feed off of soluble fiber from foods like oatmeal, lentils, apples, nuts, flaxseeds, and beans.  While many claim they benefit from taking probiotics in supplement form, the U.S. Food and Drug Administration (FDA) has approved no specific health claims for probiotics in a pill.

2. Shiitake mushrooms

Sundried, shiitake mushrooms, fatty fish, fortified dairy productions and other fortified foods are good sources of vitamin D. Vitamin D, which is actually a hormone, has been well studied for its role in mineral metabolism and skeletal health. Emerging science has found vitamin D receptors and the vitamin D activating enzyme in all types of cells throughout the body including intestine, pancreas, prostate and cells of the immune system. This has spurred further research into the role of vitamin D beyond building strong bones.

Vitamin D may stimulant the innate immune system through several mechanisms. Calcitriol, the biologically active form of vitamin D that circulates in the blood, enhances the antimicrobial effects of the immune system cells that fight against pathogens and activates production of antimicrobial proteins. Vitamin D many also indirectly play a role in the initiation of the adaptive immune response by altering the function and structure of certain monocytes, a type of white blood cell.

The body does make endogenous vitamin D when exposed to the sun, however, adequate sun exposure fluctuates throughout the year and few people get enough UV exposure during cold and flu season. With few food sources of vitamin D, many people benefit from vitamin D supplementation. The Institute of Medicine has set the recommended daily allowance for adults at 600 IU, although many clinicians recommend more (IOM sets the upper safety limit at 4000 IU).

3. Leeks

Or any of the other foods from the allium genus: onions, scallions, chives and garlic. Since ancient times, garlic has been used for cardiovascular therapies. Recent research shows its sulfur-containing compounds, specifically alliin and its unstable metabolite allicin, which is produced when garlic is cut or cooked, have antimicrobial effects against many viruses, bacteria, fungi and parasites.

Allicin may enhance the immune response by significantly stimulating the proliferation of lymphocytes. Limited intervention studies shows prophylactic treatment with garlic decreases the number of self-reported colds. While allicin is the most studied, related organosulfur compounds have been found in other allium foods as well as broccoli, cabbage, radish, asparagus and even coffee, many of which may be more palatable to take on a daily basis (unless you are also trying to ward off vampires).  

4. Honey

If you do get a cold, honey may provide some relief. A recent study showed that 2 teaspoons of honey at bed was as effective as the cough suppressant dextromethorphan. And much tastier.  Another ancient food, honey, has long been used for its medicinal properties, particularly as a topical treatment for wounds and contemporary literature describes its antibacterial and anti-inflammatory mechanisms.  Honey also has been shown to have a high antioxidant capacity due to its phenolic content with darker honeys having more antioxidant potential. Raw honey also contains other beneficial compounds including minerals, vitamins, enzymes and prebiotics (for that healthy gut flora) although if and how they work to bolster the immune system or event prevent seasonal allergies is not yet clear. Honey is a nutrient-dense choice for those looking for a local, sustainable sweetener. Just keep in mind that it does have calories (64 calories vs. 48 calories sugar, per tablespoon), although you may be able to use less since its high fructose content makes it sweeter than table sugar.

There are many other nutrients in foods that fortify the immune system. Choose ones that are colorful, less processed and delicious and eat them every day. Of course, it’s best to boost your immune system before you get sick. Adequate sleep, good hand hygiene, stress reduction, regular exercise and tobacco avoidance are all necessary habits to keep your immune system in shape.

Debbie Petitpain, RDN, is a Sodexo Wellness dietitian in MUSC’s Office of Health Promotion.




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