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The Western Diet's Far-Reaching Impact on Immunity

By Sharon Palmer, RDN

The typical way Americans eat—otherwise known as the Western diet—has been associated with numerous health risks, including heart disease, type 2 diabetes, and obesity—and now you can add one more fallout to the list: a compromised microbiome and immune function.

Scientists have characterized this diet pattern as one that focuses on highly processed foods, which are high in saturated fat, sodium, and refined sugar; and one that skimps on whole, minimally processed foods, thus low in healthful nutrients, such as omega-3s, fiber, and phytochemicals. Dietitians know this diet pattern all too well: It's a diet filled with an array of packaged foods, junk foods, and fast foods, filled with refined ingredients and fueled with few "real," nutrient-rich foods. So, it's no wonder that more and more studies have linked this eating pattern with poor health, including compromised immunity.

Western Diet and the Gut Microbiome
A new National Institutes of Health review tackling the impact of the Western diet on the gut microbiome and immune function was published last summer in the Nutrition Journal. The author investigated the current knowledge base on the effects of the Western diet on the gut microbiome, trying to paint a picture of the mechanisms by which poor eating can influence the gut and our genes that are passed along to future generations. While much of the research available on this subject has been based on in vitro and animal models, the sheer volume of data helps researchers gain a better understanding about how diet impacts immunity. The review identified key observations that Today's Dietitian shares in this article.

Obesity Weighs In
The state of obesity itself is a major factor in immunity. Animal research shows that adipocytes release inflammatory substances that can act as false alarms, which over time can cause the immune system to dial down its responsiveness.1 In addition, obese people tend to have fewer white blood cells to fight infection, and the ones they have don't work as well, which may be why they have a higher risk of infections.

Diet Choices and Immune Function
Dietary factors impact immune function, too. Processed, simple sugars reduce white blood cell phagocytosis, and possibly increase inflammatory markers. Sodium also may have a similar effect. Saturated fats, which are noted to be proinflammatory, may enhance the prostaglandin system and alter immune cell membranes, thus disrupting their function.1

The jury is still out on how omega-6 oils impact inflammation and immunity, although omega-3 fats have known anti-inflammatory effects, with benefits in a variety of conditions, such as cardiovascular disease and allergic disease.1

The Gut Microbiome and Beyond
So what does this mean for the gut microbiome? Inflammation leads to an altered host environment, shifts in immune cell membrane functions, and changes in nutrient availability, which lead to the favoring of less beneficial microorganisms in the gut over others.

More disturbing is the observation that harmful dietary effects can influence future generations. We know a mother's diet may alter many health factors in her unborn children, even down to their flavor preferences and diet choices. But a mother's diet also may influence her child's microbiome, which may be seeded into the unborn fetus while still in the womb. When a mother's diet causes a harmful imbalance of her gut bacteria, she passes this imbalance on to her unborn child, thus failing to provide an ideal immune system during a critical period and leaving the child prone to infection as well as autoimmune and allergic disease. Just as small changes that occur in the environment can have dramatic effects—for example, the loss of honeybees in an orchard—one small shift in the gut microbiota due to diet can have far-reaching effects.

— Sharon Palmer, RDN, is the nutrition editor of Today's Dietitian and author of Plant-Powered for Life.

1. Myles IA. Fast food fever: reviewing the impacts of the Western diet on immunity. Nutr J. 2014;13:61.

Strategies to Combat the Western Diet
The following tips can help your clients swap their Western-style eating pattern with a more healthful one:
Reduce the frequency of dining out. Identify how many times your clients eat out, as well as the type of restaurants they patronize, and set a reasonable goal along with action steps to help them eat more home-cooked meals.
Build better breakfasts. Let breakfast be the first opportunity of the day to swap refined, sugary grains such as pancakes, waffles, bagels, sweetened cereals, and high saturated fat offerings, such as bacon and sausage, for a more healthful start that can include whole grain oatmeal with nuts, fruit, and low-fat milk or soymilk.
Trade junk foods for fruits and vegetables. Choose fruits and vegetables at each meal and snack instead of highly processed foods, such as sugary and salty snacks, desserts, and packaged mixes. Help your clients create an individualized plan that works for them.
Ban sweetened beverages. Suggest flavorful alternatives such as home-brewed teas, and waters flavored with herbs and citrus.
— SP