Dietary Meat Categories and Descriptions in Chronic Disease Research Are Substantively Different within and between Experimental and Observational Studies: A Systematic Review and Landscape Analysis

Abstract

This systematic review and landscape analysis describes patterns in dietary meat (skeletal muscle and associated tissues from mammalian, avian, and aquatic species; i.e., muscle foods) categories (CAT) and descriptions (DESCR) used throughout nutrition-related chronic disease literature, as there is anecdotally noted variation. A total of 1020 CAT and 776 DESCR were identified from 369 articles that assessed muscle food consumption and primary prevention of cardiovascular disease, obesity, type 2 diabetes, or cancer in adults ≥19 y from PubMed, Cochrane, and CINAHL up to March 2018. Specificity of CAT was analyzed on an empirical 1-7 ordinal scale as: 1) broad/undescriptive, "fish"; 2) muscle food type, "red meat"; 3) species, "poultry"; 4) broad + 1 descriptor, "processed meat"; 5) type/species + 1 descriptor, "fresh red meat"; 6) broad/type + 2 descriptors, "poached lean fish"; and 7) specific product, "luncheon meat." Median CAT specificity for randomized controlled trials (RCTs) and observational studies (OBSs) was 3 and 2 points out of 7, respectively, with no differences between chronic disease types. Specificity of OBS CAT was higher in recent articles but RCT CAT became less specific starting in the 2000s. RCT CAT were 400% more likely to include species, 500% more likely to include leanness, but 400% less likely to include processing degree compared with OBS CAT. A DESCR was included for 76% and 82% of OBS and RCT CAT, respectively. Researchers described processed meat, red meat, and total meat CAT more commonly than poultry or fish CAT. Among processed meat DESCR, 31% included a common term used in public regulatory definitions. In conclusion, muscle food categories and descriptions are substantively different within and between experimental and observational studies and do not match regulatory definitions. A practical muscle food classification system is warranted to improve interpretation of evidence regarding muscle food consumption and chronic disease.

Keywords: animal proteins; dietary guidance; dietary intake assessment; fish; flesh foods; food group terminology; muscle foods; poultry; red meat; white meat.

FIGURE 1

Search process of a systematic review and landscape analysis assessing muscle food categorization and descriptions in chronic disease literature. *The search process and data extraction consisted of the following 3 stages: 1) potential eligibility based on information provided in the abstract, 2) confirmation of eligibility based on information provided in the full text if abstract qualified, 3) data extraction from full text articles once deemed qualified.

FIGURE 2

Country of publication for observational studies (A) and randomized controlled trials (B) included in a systematic review and landscape analysis assessing muscle food categorization and descriptions in chronic disease literature.

FIGURE 3

Top 25 most commonly used muscle food categories in observational studies (A) and randomized controlled trials (B) from a systematic review and landscape analysis assessing muscle food categorization and descriptions in chronic disease literature. The larger text implies more frequent use. Land-based and water-based muscle food frequency word clouds are presented in Supplemental Figures 1 and 2.

FIGURE 4

Trends in muscle food category specificity over time for observational studies (A) and randomized controlled trials (B) from a systematic review assessing muscle food categorization and descriptions in chronic disease literature. Results were analyzed via a least squares regression model weighted by total number of muscle food categories assessed per year and adjusted by the yearly average count of muscle food categories per article. *Total number of muscle food categories assessed that year, ^¥number of articles published that year from the final data set. Land-based and water-based muscle food category resolution showed similar trends. Observational studies adjusted and weighted R² = 0.39, coefficient for year = 0.03 (0.01 to 0.05). Randomized controlled trials adjusted and weighted quadratic R² = 0.54, transformed coefficients nonsensical.

FIGURE 5

Distribution of description factors across category resolution from a systematic review and landscape analysis assessing muscle food categorization and descriptions in chronic disease literature. Category resolution, i.e., specificity, was analyzed on an empirical ordinal scale as 1) broad/undescriptive, e.g., “fish”; 2) type of muscle food, e.g., “red meat”; 3) species, e.g., “poultry”; 4) broad + 1 descriptor, e.g., “processed meat”; 5) type/species + 1 descriptor, e.g., “fresh red meat”; 6) broad/type + 2 descriptors, e.g., “poached lean fish”; and 7) specific product, e.g., “luncheon meat.” Number of factors included in the description were analyzed on a discrete 1–5 scale.