When you talk to your patients about inflammatory bowel disease (IBD), how many of you also talk about diet? We talk to them about medication compliance, about taking their tumor necrosis factor (TNF)-alpha antagonists, about immunosuppression, but we rarely talk to them extensively about diet. I think it is really important to start doing so, and discuss putting certain things on and taking certain things off the table because of their incredible effect. A review just published in Gut prompted me to bring this up with you.
We know that IBD is an inflammation of the intestinal track. We know that there is an intestinal barrier made up by the mucus layer that is our primary defense, as well as epithelial cells and tight junctions. When it comes to the translocation of bacteria that potentially mediates disease, problems can occur when the intestinal barrier breaks. We do know that there are taxonomic changes that occur in ulcerative colitis and Crohn disease, with patients with these conditions prone to intestinal disruption and translocation.
If you are of an older generation, you will remember that we used to look at using an elemental diet, particularly in patients with IBD, including Crohn disease. However, it was thought that that was not well tolerated enough to be a mainstay of day-to-day treatment.
In the current landscape, diet is thought to potentially play a pathogenic role in gastrointestinal disorders. Past epidemiologic studies have shown that the standard Western diet (eg, high in red meat and fat, fast food) increases the odds ratio of [ulcerative colitis] by nearly five times, whereas a Mediterranean diet that is characterized by largely avoiding those foods leads to a risk reduction of nearly 70%. We have seen that in a number of epidemiologic studies, more so for Crohn disease than for ulcerative colitis.
When you talk to your patients with IBD, why is it important that you start to really scrutinize diet?
Diet plays a key role in maintaining a normal gut microbiome. Data derived primarily from animal studies shows that a high-fat, high-sugar diet impacts the microbial composition, leading to bacterial dysbiosis, which has been shown to affect gut bacteria integrity and also immunity. In rodent models deprived of fiber, there is an alternative use of carbon sources that has a direct mucosal effect. These rodents display a depleted mucus layer and its ability to protect; disruption of the barrier (ie, translocation); and in a reverse of what we would like to see, there is upregulation rather than downregulation of immune response, leading to consequent tissue damage. Rodent model studies show that going from a plant-based diet to an animal-based diet (eg, from the Mediterranean to the traditional Western) results in clear bacterial taxonomic changes that affect metabolism with alterations in bile acids, in particular sulfide metabolism, which plays a pivotal role in the pathogenesis of IBD.
We know that dietary fibers, fruits, and vegetables provide a vital substrate production of butyrate and other short-chain fatty acids that enhance the immune response. Butyrate is clearly important in affecting defensins, which protect against immune response, and cathelicidins, which protect against some of the pathogenic, enteric infections. Butyrate also downregulates transcription cytokines expressed in IBD. You also differentiate the good T-regulatory lymphocytes that decrease immune activation, which is the positive side of immune suppression. Conversely, low-fiber diets increase intestinal permeability (ie, leaky gut), thereby increasing bacterial content and facilitating the problem of translocation.
Specific Diets' Effects
In animal studies, diets high in fat and starch basically have the same effect as low-fiber diets. This has a negative impact on IBD by upregulating TNF-alpha, increasing interferon-gamma and intestinal permeability, and decreasing the levels of the good T-regulatory lymphocytes that downregulate the autoimmune response.
Another thing to be aware of is that the standard Western diet provides an incredible amount of exposure to diet emulsifiers and food additives, which can have harmful effects.
Carboxymethyl cellulose and polysorbate-80 are traditionally used in baked goods and particularly in ice cream. These are the elements that now allow us to make ice cream without the aid of a crank or addition of rock salt, for those of us old enough to remember that process. They make it easier to palletize food products and get a better sense of fullness in the mouth, but they conversely thin the mucus layer and increase gut permeability.
Maltodextrin is another additive used as a thickener and sweetener, and can also thin the mucus layer. These come from plant products, but in their highly refined form they can have the adverse effects of thinning the mucus layer, increasing gut permeability, and impairing intracellular bacteria.
Carrageenan is also used to increase texture, particularly in dairy products and sauces. These are made from seaweeds, which sounds pretty healthy, but they are again highly processed and can induce intestinal permeability.
Advising Our Patients
In the current world of IBD, we really need to have a serious discussion with our patients about these food items. We should restrict animal fat, processed foods, and processed carbohydrates. The data in support of this approach are very strong for Crohn disease. There is a bit of a data gap for ulcerative colitis, but there is no sense in waiting for those studies to appear before making similar recommendations.
There is tremendous emphasis on a translational message now, to take this message to our patients of moving toward plant-based foods, to healthy fats (eg, away from butter to olive or canola oil), to using herbs for flavor instead of salt, and to lean protein. I recommend to my patients to eat red meat rarely, less than once a week. It is basically promoting what we call the Mediterranean diet, which does allow moderate consumption of red wine.
The emphasis here that you want to provide for patients is that we have biologic evidence that this makes a difference. It is time for us to start taking a good diet history and treat patients with IBD appropriately. Start looking at diet; it has a key role in the pathogenesis of IBD and may offer a tremendous opportunity in its treatment. Hopefully this guides you to your next discussion with your patients and optimizes the outcomes.
Inflammatory Diets: The Foods and Additives That Patients With IBD Need to Avoid
David A. Johnson, MD