5 Foods That Break Down Your Immune System

The official start of winter is still weeks away, but flu season kicks into gear, oh, right about now.

1. Sugar

Sugar has been vilified by the health community for good reason — it is a zero-nutrient substance that has been linked to corroding your teeth and your brain. Susan Levin, director of nutrition education at Physicians Committee for Responsible Medicine, says a high blood sugar level also greatly reduces the ability of germ-fighting white blood cells to kill bacteria and viruses. Levin advises against eating refined and processed foods during flu season because of their high sugar content — candy, cookies, soda, and most packaged foods are all off-limits. That may be easier said than done: The American Heart Association says Americans consume 20 teaspoons of sugar on average per day.

What to reach for: High-fiber foods such as brown rice, lentils, and chickpeas will stabilize blood sugar levels and keep the immune system in check.

2. Cereal and white bread

Simple carbs contribute to the "tsunami of sugar" found in our daily diets,according to author and integrative clinical nutritionist Kathie Swift. "The average person is drowning in sugar," she said. Refined grains in cereal and bread quickly convert to glucose when digested. Can't give up your morning cereal or toast? Super-foods such as millet, buckwheat, quinoa, and amaranth are now available in cereal and bread form. Another breakfast option that boosts immunity: rolled oats with bananas, cinnamon, and a splash of organic almond milk.

3. Fatty foods

There are many reasons to eliminate fried food from your diet — here's another: High-fat diets can negatively affect your body's response to infection. Researchers Patricia Maki and Paul Newberne found that obesity and high-fat diets "depress host resistance to infectious disease and apparently influence susceptibility to some forms of cancer." Swift suggests replacing some of the animal meat you eat, which is high in saturated fat, with lentils, beans, and plants for protein. "Food is critical to immunity," she adds.

4. Alcohol

Relax — you do not have to give up your weekly glass of red wine, but Levin urges casual drinkers to reduce their imbibing during flu season. Alcohol impairs the immune system and interferes with the body's ability to ward off infections.Studies have proven that excess alcohol consumption may lead to immune deficiency and increased susceptibility to certain diseases. Experts say one drink (defined as 12 ounces of beer, 5 ounces of wine, or 1 ounce of hard liquor) will not disrupt the immune system but three or more drinks will.

5. Dairy

Many dairy products — such as store-bought yogurt — contain high levels of sugar, notes Levin. There is also a direct connection between dairy and respiratory health. Cheese, milk, ice cream, and other dairy products "can exacerbate clogging of the lungs and should be avoided," health expert Gary Null writes in The Complete Encyclopedia of Natural Healing. According to the Mayo Clinic'sJames Steckelberg, milk does not necessarily produce more phlegm but drinking it "can make phlegm thicker and more irritating to your throat than it would normally be."