Reference
Bahrami A, Shirani P, Sohouli M, et al. Dietary diversity score (DDS) and odds of colorectal cancer and adenoma: a case-control study. J Nutr Sci. 2022;11:e34.
Study Objective
To determine whether dietary diversity scores (DDS) are significantly different between newly diagnosed colorectal cancer (CRC) patients, newly diagnosed colorectal adenoma (CRA) patients, and matched controls
Key Takeaway
A higher DDS is associated with a lower odds ratio for CRC and CRA, particularly a diet highly varied in fruits and vegetables. DDS may not be a sensitive research tool for measuring differences in the risk of developing various diseases, including cancer.
Design
A hospital-based case-control study
Participants
Investigators recruited patients (aged 30–79 years) in Iran who were newly diagnosed (<3 months) with CRC (n=129) or CRA (n=130) from 3 major hospitals, along with 240 hospitalized controls for comparison. Controls were considered “healthy” and were hospitalized for traumas (25.9%, mostly fractures and sprains), surgical conditions (20.1%, mostly acute abdomen and kidney stones), nontraumatic orthopedic conditions (4.2%), and miscellaneous diseases (49.8%, including acute eye, nose, skin, and throat disorders).
Investigators assessed the patients’ usual diets before diagnosis using a food frequency questionnaire (FFQ), and they used these data to calculate their DDS.
Outcome Measures
Investigators used a version of Kant’s 1993 methodology as modified by Mirmiran to calculate dietary diversity scores (DDS) to make the food selections suitable for the Iranian diet.1,2 They used multivariate logistic regression to estimate the relationship between DDS and odds of colorectal cancer and adenoma.
Consumed food items were categorized into 5 groups: vegetables, fruits, bread and grains, meats, and dairy. These groups were divided into subgroups; for example, the vegetable group consisted of 7 subgroups: vegetables, potatoes, tomatoes, other starchy vegetables, legumes, yellow vegetables, and other green vegetables. Of note, the grain group was also divided into 7 subgroups: white bread; whole grain biscuits; pasta; breads (sangak, taftoon, barbari); noodles; rice; and barley.
One point was added to a study participant’s DDS for each half serving of a food group eaten per day with a maximum of 2 points per group. Since there are 5 groups, the highest DDS possible was 10 points and the minimum score 0.
Primary Outcome the Study Was Designed to Assess
The difference in the eating habits, as represented by DDS, in those with CRC or CRA and those without
Key Findings
After adjustment for potential confounders, an increased diversity of grains in the diet was associated with an increased risk of colorectal cancer. In contrast, increased diversity of vegetables and fruits was associated with decreased risk.
In comparing the upper versus lower tertiles, after adjustment for possible confounders, overall risk for CRC in those consuming a greater variety of grain foods was nearly triple that of those in the lower tertile (ORgrains: 2.96 [1.05–8.32]; P=0.032). Those in the upper tertile of vegetable diversity had nearly a 70% decrease in risk of CRC (ORvegetables: 0.31 [0.16–0.62]; P=0.001).
Those in the upper tertile of fruit diversity had a 63% decrease in risk (ORfruits: 0.37 [0.23–0.61]; P<0.001).
A greater diversity in vegetable and fruit consumption was also inversely associated with risk of colorectal adenoma: Those in the upper third of diversity scores for vegetable diversity had a 59% decrease in risk, and those among the higher scorers for fruit had a 44% lower risk (ORvegetables: 0.41 [0.21–0.78]; P=0.007; ORfruits: 0.58 [0.36–0.93]; P=0.021).
The cooking method was also correlated with risk; those with adenoma were more likely to grill their foods, while controls were more likely to boil.
Transparency
There is no private entity involved in the funding of this study. The authors acknowledge the “National Nutrition and Food Technology Research Institute (NNFTRI) of Shahid Beheshti University of Medical Sciences, Tehran, Iran.”
Clinical Implications
Research on the relationship between dietary diversity and disease is relatively rare, and yet we see hints that diversity is associated with significant changes in the overall risk of disease, in particular cancer. Increasing dietary diversity may be a simple and achievable goal when working with patients.
“Eat a wide variety of foods” was the fundamental advice given by nutritional experts long ago during my college nutrition courses. Yet we have seen few attempts to define or measure such variety. It is only in recent years that studies reporting on dietary diversity are being published regularly.
The first such study reporting on dietary diversity that came to this writer’s attention was Ghadirian’s 2009 paper on breast cancer risk in women with BRCA mutations.3 That small study compared dietary diversity scores among a group of 38 French Canadian BRCA carriers and their eventual risk of being diagnosed with breast cancer. Among those scoring in the top 25% of dietary diversity, risk of breast cancer was 73% lower than those in the lower 25%.
Given how little information was available at that time on how we might influence BRCA risk, this study garnered a solid share of attention.
Three separate papers were published in 2008 by Werner Garavello examining the relationship between dietary diversity in pharyngeal, laryngeal, and squamous cell esophageal cancers. After adjustments for confounders and comparing upper versus lower tertiles of dietary diversity score, overall risk (OR) for pharyngeal cancer was 0.78.4 Similarly, a significant inverse association was seen in laryngeal cancer for vegetable diversity (OR=0.41, 95% CI: 0.28–0.59, for the highest versus the lowest quartile) and fruit diversity (OR=0.40, 95% CI: 0.27–0.59).5 Risk of esophageal cancer was also lower in those with higher dietary diversity. Again, upper versus lower quartiles, high vegetable diversity and fruit diversity were inversely associated (OR=0.34 and 0.51, respectively).6
Recently, in 2022 Mirjalili et al compared 60 cases of prostate cancer with 60 controls and reported an inverse association such that “higher adherence to DDS (OR = 0.33; 95% CI (0.11-0.97)), fruits group (OR = 0.19; 95% CI (0.06-0.63)), and vegetables group (OR = 0.17; 95% CI (0.05 - 0.58)) were significantly associated with lower risk of PC.” However, “greater adherence to the meat group (OR = 3.88; 95% CI (1.32-11.42)) was significantly associated with increased PC risk.”7
These and other studies taken together would suggest that we should encourage those at high risk of cancer or those with a history of cancer and perhaps even those living with cancer to eat a diverse diet with as wide a variety of fruits and vegetables as they can.
The cooking method was also correlated with risk; those with adenoma were more likely to grill their foods, while controls were more likely to boil."
Before we jump wholeheartedly into pushing this idea of diversity, there are a few caveats. For one, the discovery that diversity scores correlate with cancer risk is an incidental finding. This is not what the DDS was designed to do. While there is no rule that says an analytic tool cannot be repurposed, we should still factor in what else these scores were designed to tell us. The entire concept of DDS calculation was developed to assess dietary quality in economically challenged demographic groups. DDS is indeed an accurate method to quickly assess the micronutrient status of an individual’s diet.8,9 The score is meant to spot malnourishment rather than ideal status. To score poorly on a DDS evaluation strongly suggests a significant level of malnourishment.
In these studies, the diversity score may only be a metric for comparing malnourished individuals with slightly better-fed individuals. In other words, these findings don’t tell us if there is a benefit when comparing adequately nourished to very well-nourished individuals. We can’t use this information to know whether a vegetable juice smoothie will provide additional benefit over a nutrient-dense, plant-based diet.
Recall that a top score among Bahrami’s study participants was a 10, a ranking achieved by eating half a serving of each food group (vegetables, fruits, bread and grains, meats, and dairies) per day. To earn a maximum score for fruit or vegetable consumption merely required eating a serving a day of each. Most of us encourage patients to follow the “5 a day” recommendation when it comes to fruits and vegetables, at a minimum.
Beyond nutritional status, DDS scores can also be employed to stratify a population by economic status. More affluent people tend to consume a more diverse diet. Economic status, as we are aware, is closely related to health status.10 Although DDS is calculated via food consumption data, it categorizes individuals by economic status, and that may be the influencing factor.
Perhaps a better study for us to consider is Otsuka et al’s 2020 paper, which examined dietary diversity and all-cause specific mortality in older Japanese adults. This was a relatively large study that followed 386 men and 413 women over a mean period of 15.7 years. During that time, 289 subjects died. The study used a more thorough measure of diversity, a questionnaire that carefully recorded a 3-day period of foods consumed with the results categorized into 13 food groups.
Otsuka reported that compared to the subjects in the lowest tertile, the multivariate-adjusted HR for all-cause and cancer mortality was 0.69 (CI: 0.51–0.94) and 0.57 (CI: 0.33–0.98), respectively, in subjects in the highest tertile of dietary diversity. There were no significant associations between dietary diversity score and death from cardiovascular or cerebrovascular disease. Eating a variety of foods might contribute to longevity in older Japanese community dwellers.11
The finding that greater diversity scores in grains eaten were associated with nearly triple the risk of colorectal cancers needs some consideration. Sliced loaf bread, as eaten in the United States, is uncommon in Iran. There are 4 common types of bread eaten there; all would be considered “flatbreads,” and only 1 type is traditionally made with whole wheat flour. The easiest way to understand these findings is to know that “in the present study, cancer patients consumed lower amounts of whole grains and higher amounts of refined grains.” The majority of Iranian bread is made from refined white flour regardless of shape and baking methods. Those who earned higher scores for consuming diverse bread types may have just consumed more white flour rather than a diversity of whole cereal grains.
When we consider data from elsewhere, a 2011 meta-analysis of 8 studies reported a decreased CRC risk with high consumption of whole grains.12 The idea that whole grain consumption is beneficial still has strong support in most circles and isn’t about to be discarded based on these findings alone. The idea that greater consumption of simple carbohydrates, even if in a variety of different forms, increases risk of CRC remains in keeping with our current guidance.
The other thing we need to do is look more closely at the scores in these studies. Consider how the DDS was calculated in Bahrami’s colorectal cancer study. Each half serving of a food group counted for 1 point, with a maximum of 2 points per food group awarded. Since there were just 5 groups, 10 points was the total possible score. A patient with a top score may have consumed just a serving each in total of fruit, vegetable, bread, meat, and dairy products. The mean score in this study was only 6. These studies are not really telling us about the benefits of eating 5 servings a day of fruits and vegetables, but rather they’re comparing a mediocre diet against an even more minimal diet that is on the verge of malnourishment. While we intuitively want to believe that if a few fruits and vegetables are good for us, then more should be better, these data do not tell us whether the benefits of a healthier diet will reach a plateau with increasing consumption.
