How Diet Affects Psoriasis

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Editor’s Note: This story is part of a new series on HealthCentral called “Get Your Ph.D.!”, which is geared toward people who’ve got the basics of their condition down and want to up their expertise. Who’s ready to go pro?!

Scientists have long known that obesity and psoriasis go hand-in-hand. Like chips and salsa or gin and tonic, if you have one disease, you’re likely to have the other. The reason is that a high BMI can lead to inflammation in the body, which increases the risk for developing the challenging skin condition known as psoriasis—or worsening existing symptoms if you already have it. Now, a new study published in the Journal of Investigative Dermatology suggests there may be another mechanism at work: Fat cells themselves may not be the culprits, say researchers, but rather specific types of foods are to blame.

In the study, conducted at the University of California, two groups of mice were fed different diets. Once group got a typical mouse meal; the other one was given a characteristic “Western diet” (basically, the mouse equivalent of a moderate-to-high fat, processed-sugar diet that mimicked what humans would eat on the same meal plan). The mice kept it up for four weeks, after which scientists took stock of their skin, and found that the creatures who’d been chowing on the rodent version of burgers, fries, and shakes showed visible inflammatory changes including redness, scales, and thickened skin—the same hallmark symptoms consistent with human psoriasis—even if the mice hadn’t appreciably gained weight.

“This is important because many people think that it’s obesity alone that leads to the increased risk for psoriasis,” says senior study author Sam T. Hwang, M.D., Ph.D., department chair and professor of dermatology at the University of California Davis School of Medicine. “What this shows is that dietary changes can have a radical impact on the skin—so it’s not just weight that makes a difference for developing psoriasis, but the types of foods you eat.”

These so-called “Western” foods are typically high in saturated fat (butter, red meat, cheese and other dairy products made from whole milk, for example), plant-based oils (such as palm oil, coconut oil, and canola oil) and processed ingredients, like those in many baked goods. The foods also contain high levels of simple sugars, found in fruit juices, soda, candy, and even some whole fruits like apples, bananas, and watermelon.

A Gut Reaction

So, what is it about these foods, common in American diets, that causes inflammation in the first place? Researchers believe they alter the composition of the microbiome, those billions of bacteria living in your gut that help maintain general health and the health of your immune system. Changing the balance of these bacteria through diet may ultimately lead to an inflammatory response related to psoriasis.

To break it down even further (we know, it’s complicated), “high-fat foods cause bile acids from your gall bladder and liver to go into the gut to help with digestion,” says Ronald Prussick, M.D., an assistant clinical professor of dermatology at George Washington University and medical director of the Washington Dermatology Center. “These acids then cause bad bacteria to form, leading to inflammation inside the body.”

What this all means: The study proposes that what you eat can alter the gut microbiome, causing changes in bile acid levels, which can affect inflammation.

This theory was tested in the study when the researchers administered cholestyramine, a drug used to lower cholesterol (high levels of which are found in fast foods and other “western” fare), to the mice and found that it helped reduce the risk of skin inflammation. “Cholestyramine was shown to bind to bile acids in the intestine and release through the stool, allowing for inflammation to be lowered in the mice,” Dr. Hwang says.

Food for Thought

Doctors have long maintained that there is no single food that can treat or cure psoriasis, and that’s still true. But if you have the skin condition or are at risk for the disease (which is frequently genetically determined), limiting or eliminating foods high in saturated fats and simple sugars can lessen the chances for inflammation—and therefore possibly psoriasis, Dr. Hwang says.

What to eat instead? A Mediterranean-type diet, characteristically rich in healthy fats and omega-3 fatty acids, is known to help fight inflammation. It includes foods such as olive oil, avocados, nuts, seeds, fish like salmon and lake trout, and some meat or dairy from grass-fed animals, as well as fresh vegetables and fruits low on the glycemic index, like berries. “Switching to a healthier diet can increase the chances of treating psoriasis more effectively,” says Dr. Prussick.

Additionally, Dr. Prussick suggests cooking on lower heat by stewing, poaching, boiling, and steaming foods rather than grilling, frying, or toasting them. “Heat causes sugars in foods to bind to proteins, known as advanced glycation end products (AGEs), which causes more inflammation,” he says. He also recommends cooking with acids such as vinegar or lemon juice, which can reduce AGEs by 50%.

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