Data from this large prospective cohort of men followed for 18 years indicate that frequent nut, corn and popcorn consumption are not associated with an increased risk of diverticular complications. Indeed, nut and popcorn consumption appear to be inversely associated with the risk of diverticulitis independent of other known or potential risk factors including age, body mass index, dietary fat, fiber and red meat, physical activity, cigarette smoking and the use of non-steroidal anti-inflammatory drugs and acetaminophen. No associations were found between nut, corn or popcorn consumption and diverticular bleeding.
To our knowledge, no prior study has examined the association between nut, corn or popcorn consumption and diverticular complications. Nonetheless, in a recent survey of colorectal surgeons, 47% felt that patients with diverticular disease should avoid these foods.8
The commonly held belief that these foods can incite complications of diverticulosis, and the recommendation that individuals with this condition avoid them apparently evolve from the theory that luminal trauma is a causal mechanism.5
In this model, inflammation or bleeding is precipitated when a fecalith or particulate fecal material lodges within a diverticulum and erodes the mucosa.1, 13
Foods with poorly digested particles, such as nuts, corn, and seeds are presumed to be particularly abrasive, or apt to lodge within diverticula. While fecal matter is commonly found within wide-necked diverticula, the relationship between the ingestion of a particular food and subsequent trauma to a diverticulum is largely speculative, and the exact mechanisms leading to diverticular complications are not known.
The differences in our results with respect to diverticulitis and diverticular bleeding may be explained by potentially distinct mechanisms underlying these complications. A histological study of bleeding colonic diverticula found an absence of mucosal inflammation or evidence of diverticulitis at the bleeding sites.42, 43
Abnormalities were confined to the vasa rectum and included eccentric intimal thickening near the site of bleeding, and asymmetric rupture towards the lumen, findings consistent with a nonspecific vascular response to injury.
There are several plausible mechanisms by which nut intake may protect against diverticulitis, although our data do not enable us to make causal inferences. Nuts are rich in nutrients with anti-inflammatory properties such as vitamin E, α-linolenic acid and other unsaturated fatty acids, and phytochemicals. Nut consumption is inversely correlated with levels of inflammatory markers including C-reactive protein and interleukin-6,24
and is protective against certain inflammatory disease states.22, 27, 28
The high mineral content in nuts including zinc and magnesium may also favorably influence the colon. Alterations in the structure and content of collagen in the colon have been noted in diverticular disease, which may in part be due to decreased expression of zinc-containing endopeptidases.44, 45
Magnesium may reduce oxidative stress in the colon, a mechanism that is also postulated for the inverse association seen between magnesium intake and colon cancer.46, 47
Popcorn is less nutrient dense than nuts, but does contain lutein, a micronutrient with anti-inflammatory and chemoprotective properties that is also found in nuts, as well as modest amounts of magnesium.
The high fiber content of nuts and popcorn does not appear to provide adequate explanation for the observed inverse associations between nuts and popcorn and diverticulitis. The multivariable analyses adjusted for total dietary fiber intake, and the consistency between the age-adjusted and multivariable models does not imply significant confounding by fiber or the other covariates. Nor do nuts and popcorn appear to be markers for generally healthy habits, since the data on other lifestyle and dietary factors such as physical activity and red meat consumption do not suggest a health conscious pattern in men with frequent nut and popcorn consumption. Notably, the majority of our data were acquired during a time period when nuts were not perceived as a healthy food. Nonetheless, given the observational nature of the study, we cannot exclude the possibility of residual confounding by a lifestyle or other unmeasured factor.
We were unable to specifically study the effect of nut, corn and popcorn consumption in men with established diverticulosis because the presence of diverticulosis was not known at baseline in all individuals. Men with known asymptomatic diverticulosis likely represent a biased subset of men who have undergone lower endoscopy or colon imaging, and men with known diverticulosis are likely to alter their behaviors including decreasing the consumption of nuts, corn and popcorn. However, the prevalence of undiagnosed asymptomatic diverticulosis was presumably quite high in this cohort of middle-aged and elderly men, and therefore, our findings likely apply to patients with established diverticular disease.
A long-term influence of nut and popcorn consumption on the development of diverticulosis does not appear to account for the inverse associations with diverticulitis observed in this study. We did not find significant associations between nut and popcorn consumption and incident uncomplicated diverticulosis. Furthermore, our results remained unchanged after adjustment for baseline consumption. The later analysis aims to distinguish the independent effect of very recent diet (relevant to the risk of diverticular complications) from past diet (relevant to the development of diverticulosis).
In the 2-year time lag analysis, the inverse relationship between nuts and diverticulitis was strengthened, but the results for popcorn were attenuated. Some men may have reduced their consumption of popcorn in response to symptoms of undiagnosed diverticulitis under the assumption that popcorn is harmful. However, if recent popcorn is protective, their subsequent risk of diverticulitis would increase. This would enhance the inverse relationship seen between popcorn consumption and diverticulitis in the standard analysis, and attenuate it in the time lag analysis. Overall, there was no evidence from the time lag analysis that consumption of nuts, popcorn or corn was positively associated with diverticular complications.
Our study has certain limitations. As noted above, it is possible that the associations found between nuts and popcorn were the result of residual confounding. In addition, diverticular complications and dietary intake were based on self-report. However, several factors limit the possibility of misclassification bias. Study participants were health professionals, review of 179 medical records endorsed the validity of self-report, and secondary analyses supported our findings. Food consumption was assessed prior to the development of diverticular complications using a validated food frequency questionnaire. On the whole, any misclassification bias would likely be random, and thus would weaken any true association. The generalizability of our results to younger patients and women may be limited. However, diverticulosis is rare before the age of 40,1
and there are no clear gender differences in diverticular disease.1, 48
Lastly, we were unable to directly examine the relationship between seed consumption and diverticular complications. However, consumption of strawberries and blueberries (fruits with small seeds) was not associated with diverticular complications.
In conclusion, our results suggest that nut, corn and popcorn consumption are not associated with an increased risk of incident diverticulitis or diverticular bleeding, and may be protective for the former. These findings refute the pervasive but unproven belief that these foods invoke diverticular complications, and suggest that the recommendation to avoid these foods in diverticular disease should be reconsidered.