The Effect of the Meat Factor in Animal-Source Foods on Micronutrient Absorption: A Scoping Review.

The EAT-Lancet Commission's planetary health guidelines suggest a reduction in the consumption of animal-source foods for better health and more sustainable food systems. Animal-source foods are highly nutrient-dense, therefore suited to address the widespread issue of micronutrient deficiencies, particularly in low-resource settings where diets are predominantly plant-based. Animal-source foods are also believed to contain the meat factor, a substance enhancing the absorption of micronutrients from plant-based foods. We conducted a scoping review with the objective of systematically mapping the available evidence on the meat factor. The MEDLINE/Pubmed and Web of Science Databases were searched for literature published up to September 2021. Articles eligible for inclusion were all studies assessing the effect of adding animal-source foods and/or animal-source foods fractions on the micronutrient absorption from a plant-based meal or the overall diet in animal models and human subjects. Screening and data extraction were performed, and results were charted into 12 categories. We identified 77 articles eligible for inclusion, 52 of which were conducted in human subjects, 24 in animal models and one in both. The addition of muscle tissue and muscle tissue fractions to single plant-based meals steadily increased absorption of iron and zinc across studies. The efficacy of the meat factor in increasing iron and zinc absorption in the overall diet is less clear. No clear differences emerged between red meat, poultry and fish in promoting the meat factor effect. No clear evidence indicates that milk and egg products contain the meat factor. Our review highlights the importance of muscle tissue for the potential of the meat factor to enhance absorption of micronutrients of concern. While the literature supports including sustainable and economically accessible forms of these animal-source foods into the diet, we found limited studies in resource poor countries and of diets with low meat intake.