Systematic review and meta-analysis of diet quality and colorectal cancer risk: is the evidence of sufficient quality to develop recommendations?

Figures & data

Table 1. The overall quality of evidence on diet quality quantified by dietary indices on the risk of CRC in pooled findings from eligible observational studies^a.

Certainty assessment							Summary of findings
No of studies	Study design	Risk of bias	Inconsistency	Indirectness	Imprecision	Considerations	Effect Size (95%CI)	Certainty
DII and CRC
11	Observational	Not serious	Serious^c	Not serious	Not serious	Restricted to published findings	OR 0.66 (0.56–0.78)	(Score −2)
MDS and CRC
16	Observational	Not serious	Serious^c	Not serious	Not serous	Publication bias and restricted to published findings	OR 0.84 (0.78–0.90)	(Score −2)
DASH and CRC
8	Observational	Not serious	Not serious	Serious^d	Not serious	Restricted to published findings	OR 0.80 (0.77–0.84)	(Score −2)
HEI and CRC
8	Observational	Not serious	Serious^c	Serious^e	Not serious	Restricted to published findings	OR 0.72 (0.64–0.80)	(Score −3)

^a The quality assessment was based on GRADE approach.

^b Overall certainty was downgraded due to the observational design of included studies, inconsistency, indirectness, and detected publication bias.

^c High levels of heterogeneity in the pooled findings.

^d Results restricted to US/Canada.

^e Limited findings from US/Canada/Asia.

Abbreviations: CI, confidence interval; CRC, colorectal cancer; DASH, Dietary Approach to Stop Healthy Index; DII, Diet Inflammatory Index; GRADE, Grading of Recommendations Assessment, Development, and Evaluation; HEI, Healthy Eating Index; MDS, Mediterranean Diet Score; US, United States.

Figure 1. Flow chart of inclusion of relevant studies.

Figure 2. Summary risk estimates for CRC comparing the highest to lowest diet quality.

The data are stratified by study design (i.e., cohort studies/case-control studies), geographic region (i.e., US/Canada, Europe, Central Asia) gender (i.e., men, women), tumor site (i.e., colon and rectal cancers), and overall estimate. The summary risk estimates are pooled ORs for CRC comparing the effect of diet quality by the DII, MDS, DASH, and HEI. For the DII, diet quality is highest with the lowest categories and lowest with the highest categories. For the MDS, DASH, and HEI, diet quality is highest for the highest categories and lowest for the lowest categories. Abbreviations: CRC, colorectal cancer; DASH, Dietary Approach to Stop Hypertension; DII, Diet Inflammatory Index; HEI, Healthy Eating Index; MDS, Mediterranean Diet Score; OR, odds ratio; US, United State

Box 1. The dietary indices used to quantify diet quality.

IDiet quality index	Origin of the index	Included food components
DII	Based pro/anti-inflammatory association of dietary components with inflammatory biomarkers, including IL-1β, IL-4, IL-6, IL-10, TNF-α	Includes 19–45 dietary components Pro-inflammatory components: Carbohydrate, Protein, total fat, Saturated fatty acids, Cholesterol, Vitamin B12, Fe, Alcohol, Energy. Anti-inflammatory components: Onion, Saffron, Garlic, Ginger, Fiber, Folic acid, Caffeine, MUFA, PUFA, n-3 fatty acids, n-6 fatty acids, Niacin, Riboflavin, Vitamin B6, β carotene, Mg
MDS	Based on evident role of foods components in cardiovascular health	Includes 8–11 food components: Foods with beneficiary effects: Cereals, vegetables, Fruits, Legumes, Nuts, Olive Oil, Fish, High ratio of MUFA + PUFA /SFA Foods with adverse effect: Milk and dairies, Meat and processed products, sweets, sweetened beverages, Saturated fatty acids, Cholesterol, Alcoholic beverages, Alcohols (consuming (alcohol >50 gr/day alcohol)
DASH	Based on evidence on diet elements related to hypertension management	Food groups: Fruits, Vegetables, Red meat, low fat dairies, Sugar-sweetened beverages, Oils, Whole grains, Nuts, and Legumes.
HEI	Based on healthy eating guidelines without specific mechanism	Foods with beneficiary effect: Fruits, Vegetables, Whole grain, beans, Dairy, Total protein in food, sea food, PUFA + MUFA/SFA ≥ 2.5 Foods with adverse effect: Sodium, Empty calorie, refined grains, PUFA + MUFA/SFA < 1.2

Abbreviations: DASH, Dietary Approach to Stop Hypertension; DII, Diet Inflammatory Index; HEI, Healthy Eating Index; IL, Interleukin; MDS, Mediterranean Diet Score; Mg, Magnesium; MUFA, monounsaturated fatty acids; PUFA, Poly Unsaturated Fatty Acids; SFA, Saturated Fatty Acids.