Abstract
While commission reports and nutritional guidelines raise concerns about the effects of consuming red meat on human health, the impacts of how livestock are raised and finished on consumer health are generally ignored. Meat and milk, irrespective of rearing practices, provide many essential nutrients including bioavailable protein, zinc, iron, selenium, calcium, and/or B12. Emerging data indicate that when livestock are eating a diverse array of plants on pasture, additional health-promoting phytonutrients—terpenoids, phenols, carotenoids, and anti-oxidants—become concentrated in their meat and milk. Several phytochemicals found in grass-fed meat and milk are in quantities comparable to those found in plant foods known to have anti-inflammatory, anti-carcinogenic, and cardioprotective effects. As meat and milk are often not considered as sources of phytochemicals, their presence has remained largely underappreciated in discussions of nutritional differences between feedlot-fed (grain-fed) and pasture-finished (grass-fed) meat and dairy, which have predominantly centered around the ω-3 fatty acids and conjugated linoleic acid. Grazing livestock on plant-species diverse pastures concentrates a wider variety and higher amounts of phytochemicals in meat and milk compared to grazing monoculture pastures, while phytochemicals are further reduced or absent in meat and milk of grain-fed animals. The co-evolution of plants and herbivores has led to plants/crops being more productive when grazed in accordance with agroecological principles. The increased phytochemical richness of productive vegetation has potential to improve the health of animals and upscale these nutrients to also benefit human health. Several studies have found increased anti-oxidant activity in meat and milk of grass-fed vs. grain-fed animals. Only a handful of studies have investigated the effects of grass-fed meat and dairy consumption on human health and show potential for anti-inflammatory effects and improved lipoprotein profiles. However, current knowledge does not allow for direct linking of livestock production practices to human health. Future research should systematically assess linkages between the phytochemical richness of livestock diets, the nutrient density of animal foods, and subsequent effects on human metabolic health. This is important given current societal concerns about red meat consumption and human health. Addressing this research gap will require greater collaborative efforts from the fields of agriculture and medicine.
Highlights
Navigating discussions on red meat and human and environmental health are challenging
In addition to reducing per capita consumption of meat in industrialized countries (Godfray et al, 2018), human and environmental health can be enhanced through livestock management practices that promote good land stewardship, limit environmental impacts (Wepking et al, 2019; Andrews and Johnson, 2020; Richter et al, 2020; Rosenzweig et al, 2020), and enhance the healthfulness of meat and dairy products (Provenza et al, 2019)
While public health recommendations are for reducing red meat consumption to reduce risk of metabolic disease, no consideration is given to animal production practices in these dietary recommendations
Summary
Navigating discussions on red meat and human and environmental health are challenging. In the field of human nutrition, a wealth of epidemiological data associate animal food consumption, red meat, with increased risk of cancer (Chan et al, 2011), cardiovascular disease (Zhong et al, 2020), obesity (Wang and Beydoun, 2009), and diabetes (Micha et al, 2012) This has led to widescale public health recommendations by the American Heart Association (Arnett et al, 2019), the World Health Organization (Bouvard et al, 2015), and the Dietary Guidelines for Americans (USDA, 2015) to reduce red meat consumption in an effort to halt metabolic disease. We discuss the information currently available on the wide range on phytochemicals found in grass-fed meat and dairy products and evaluate their potential health effects
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