This paper was interesting to me because QB has been following a mostly vegetarian diet to help control his ulcerative colitis and IBS. I wanted to summarize the conclusions in this paper for myself, QB, and all you readers. This paper was made available via the CR Society archives, so then link will take you there instead of to the pdf.
Researchers wanted to study the proposed connection between animal protein consumption and increased risk for IBD. The study consisted of 67,581 women living in France between the ages of 40-65 without major diseases at the beginning of the study. The study was conducted over 10.4 years, and questionnaires on lifestyle were given ever 24 months along with an clinical IBD assessment. During the study, a total of 77 cases of IBD were diagnosed during the study, and 458 women checked Crohn’s disease or Ulcerative Colitis on the questionnaire. (further details in link)
High protein intake, specifically animal protein, was significantly associated with increased risk of IBD (particularity for Ulcerative Colitis). Meat and fish, were particularly associated but not eggs or dairy (but eggs or dairy may not have been eaten in as large of quantities).
Specifics of the Results:
In the adjusted model, only total protein intake (not carbs or fats) was associated with an increased IBD risk. Interestingly, only animal protein exerted this IBD risk with no association observed with plant protein. Also, differences between UC (ulcerative colitis) and CD (Crohn’s Disease) were observed. CD was most correlated to total protein intake as opposed to animal or plant, while a strong association was seen with animal protein and UC.
How is moderate to high protein intake defined in this study?
Protein intake fell into three average intake groups. The first was 1.08g/kg, the second was 1.52g/kg, and the third intake group averaged in at 2.07g/kg. High protein intake saw a 3.3 fold risk of developing IBD.
Why might animal protein cause an increased IBD risk?
The small intestines do not adsorb some of the heme and amino acids contained in animal proteins. These are then passed to the colonic lumen and are metabolized by the micro-flora. Products from these reactions include hydrogen sulfide, phenolic compounds, amines and ammonia which are toxic to the colon.
Sulfide may alter the cell membrane of the intestinal wall cells leading to loss of barrier function which in turns triggers an immune response.
Even in healthy people, it has been shown that an increase in dietary protein leads to changes in colonic metabolism which is reflected by an increase in fecal ammonia, fecal volatile sulfur compounds, and urinary p-cresol.
Obviously, one limitation of this study was that it only included middle aged women, but these results highlight the need for additional studies in the younger and male population.