Inflammatory Bowel Disease (IBD) is an umbrella term for a group of complex and multifactorial disorders affecting the intestinal tract. As the name implies, acute and chronic inflammation of the intestine is a major symptom in IBD. Crohn's disease and ulcerative colitis are two of the main disorders captured under IBD, and both conditions are characterized by relapsing inflammation of the intestinal tract.
IBD onset is typically in patients between 20 to 40 years of age and usually persists for life, although disease symptoms can be unpredictably exacerbated or occur intermittently, followed by variable-length periods of remission. Although the highest disease incidences are currently in Canada and Europe, incidence rates are increasing worldwide.
Ulcerative Colitis (UC) and Crohn's Disease (CD)
Though both Crohn's disease and UC fall under the IBD banner and present with similar symptoms, the physiology of the disease within the intestine as well as the histologic (tissue) changes are different in each condition.
A Perfect Storm
A few factors - genetic predisposition, environmental factors, and alterations in the intestinal microbiome - combine in a perfect storm to bring about the inflammation that is characteristic of IBD.
Aspects of the modern “western diet” may act in concert with these aforementioned factors to exacerbate the onset of IBD because genetics, microbes, and what we eat are all factors in maintaining the balance of gut health, a.k.a "homeostasis. When all these factors are in synergy, gut health is optimized, but when the synergy is disrupted, health can be adversely impacted. Disruption of any single factor can tip the system toward IBD, but alone is insufficient to single handedly cause IBD.
Of all these factors, we know the most about the genetics of IBD.
The genetics of IBD
Over 160 loci have been linked to increased IBD susceptibility. These loci implicate a wide and diverse lineup of genes that code for a whole range of physiological processes, mainly:
- Microbe recognition
- Lymphocyte activation, and
- Intestinal epithelial defense.
Environmental factors contributing to IBD
One of the main theories behind increased IBD incidence is the "hygiene hypothesis:" given highly sanitized conditions in developed countries, it's possible that crucial early childhood exposure to a variety of enteric germs fails to occur. As a result, there are crucial gaps in the "training" of immune response.
Another prominent theory is the "cold chain hypothesis," which suggests that prolonged refrigeration of foodstuff promotes the growth of psychotropic bacteria such as Yersinia and Listeria.
In addition, certain drugs and activities - for example, non-steroidal anti-inflammatory drugs, alcohol, smoking, or bacterial toxins - have been observed to damage intestinal epithelial barrier properties.
Behind all of these hypotheses is the underlying idea that any disbalance of intestinal gut flora can potentially trigger immune responses implicated in IBD.
The connection between IBD and diet
A typical "Western diet," one rich in animal fat and protein but low in diverse fibers - has been strongly linked to the development of IBD. A high intake of digestible carbohydrates, starch, and refined sugar has also been shown to upset the gut microbial balance.
Omega-6 polyunsaturated fatty acids and long-chain fatty acids, in addition to the above, act in concert to alter the bacterial components of the microbiome, increasing intestinal permeability and promoting inflammation. The mechanisms of protein-induced inflammation are not yet fully understood, but the consumption of red meat is thought to be a factor in IBD relapse.
Obesity is another fallout of a high-fat diet that, like IBD, is characterized by inflammation and elevated levels of proinflammatory cytokines and adipokines.
On the bright side, high vegetable intake can lower the risk of UC, and greater intake of fiber and fruit can lower the risk of CD. Omega-3 fatty acids, medium-chain triglycerides (MCTs) and nondigestible carbohydrates improve these parameters and thus overall intestinal well-being.
Exclusionary diets, where one food category is left out, have also shown some efficacy in relieving the symptoms of IBD. Further research will reveal how diet can be leveraged to improve the quality of life of patients with IBD.