For the first time, in a large prospective study, researchers have identified an association between high protein intake and a significantly increased risk of inflammatory bowel disease (IBD). While doctors have long suspected that diet contributes to IBD, little has been assessed, and the studies conducted have been retrospective, which are less informative because they rely on the study participants' ability to recall what they have consumed in the past. This study examined the effects of different sources and amounts of protein.
Using participants in France's E3N cohort study, researchers led by Prevost Jantchou, MD, of the Center for Research in Epidemiology and Population and colleagues identified 77 women ages 40 to 65 with validated cases of IBD. In each case, the onset of IBD occurred after the first dietary questionnaire was administered, thereby assuring that they could be studied prospectively.
Dr. Jantchou examined participants' macronutrient (protein, fat and carbohydrate) intake, and determined that more than two-thirds of them had elevated levels of protein intake. Participants were divided into three groups based on their mean protein intake: the lowest intake group had a mean daily protein intake of 1.08 grams/kg of body weight; the middle group had 1.52 grams/kg; and the highest group had 2.07 grams/kg. The FDA recommends a daily intake of 0.8 grams of protein per kilogram of body weight.
When examining the effects of specific types of protein, Jantchou found that animal protein represented a threefold risk of developing IBD in the highest group compared to the lowest group. Specifically, animal protein from meat and fish, not dairy, created an increased risk, while vegetable protein created no increased risk of developing IBD.
Researchers found that the increased risk from animal protein intake were the same for Crohn's disease and ulcerative colitis. They also found that smoking and hormonal therapy, two factors known to be related to the risk of IBD, did not change their results.
"Our findings represent a tremendous step forward in our understanding of inflammatory bowel disease," said Dr. Jantchou. "For years we've known there was a connection between diet and IBD, and we now know specifically which aspect of diet is related to disease occurrence. The next step is to look at the effect of animal protein in patients already diagnosed with IBD to be able to give them better dietary advice."