This question is a hot topic in the debate about how to produce enough nutritious food sustainably for a growing global population, expected to reach approximately 10 billion by 2050. Animal-source foods (ASFs) are controversial, political and personal. What is the evidence for their role in human health? The environment?
This blog is based on a conference hosted by the University of California, Davis, on 14–15 May 2019 titled "Aligning the Food System for Improved Nutrition in Animal-Source Foods". It aims to offer a window into recent scientific research and thinking.
First of all, a caveat. Participants were attending a conference on the importance of ASFs, so those favoring low or no ASF consumption were underrepresented or perhaps altogether absent. As a result, it had a sort of preaching-to-the-choir feel, which limited rigorous debate. Nevertheless, it generated an important finding of relevance to the wider debate—participants agreed that the current way of producing ASFs is largely unsustainable globally, especially in light of climate change and population growth. Moreover, there was much discussion on the challenges of setting optimal amounts or ranges of ASFs and how this varies among subgroups.
The conference began with a series of presentations on the importance of ASF for human health, particularly for infants, young children, adolescents and pregnant women. Interestingly, Lora Iannotti began the first session with an overview of the evolutionary perspective on ASF nutrition. Paleolithic diets on average were far higher than modern diets in ASF (30–70% of energy), protein (~30% of energy), fat (~35%, including more omega-3 and less omega-6 fats), fiber, micronutrients and beneficial bioactives, and they contained trivial amounts of grains, no refined grains, sugar or processed foods. Yet our ancestors as well as existing cultures that have maintained traditional diets and lifestyles post industrial revolution have a low burden of chronic disease. Furthermore, brain size and height were higher and infection lower before the advent of agriculture 10 millennia ago.
Several examples were provided of evidence for strong correlations between ASF consumption with child growth and cognitive development as well as causal evidence from randomized controlled trials. Some, but less attention was given to potentially harmful impacts of ASFs, such as the association between red and processed meat with colorectal cancer. This was unsurprising given the limited selection of presenters discussed above, and more discussion of the controversies in ASF nutrition would have been beneficial.
Many presenters highlighted the high density of bioavailable nutrients in ASFs compared to most plant foods. An example was given that you would need to consume ~8 times more spinach than beef liver to obtain the same amount of iron. This large difference is attributable primarily to bioavailability, since beef liver only has about twice as much iron by weight as spinach. Of course, other factors in the diet influence absorption, so it’s difficult to predict absorption in any individual. Lindsay Allen pointed out more generally, that diets low in ASFs are often lacking in key vitamins—she cited vitamin B12 (ASFs are the only dietary source, vitamin A (ASFs are the only preformed source), iron (ASFs are the only dietary source of heme), zinc (ASFs are especially bioavailable), calcium, choline and vitamin D (ASFs are the only dietary source).
Does an "egg per day" keep the doctor away?
If you accept that ASFs are important for human health, the obvious question is how much should be consumed at the population level and among vulnerable groups? The EAT Lancet diet recommends an average of 14% of energy from ASFs (although as little as 0%), while other diets like the DASH diet 30-35% and evolutionary diets (for > 99% of hominin past) ~30-70% of energy from ASFs. While it’s clear that you can carefully construct a diet very low in ASFs to meet nutrient requirements, there is concerning evidence that populations with low ASF consumption are more prone to nutrient deficiencies, particularly vitamin B12, iron and zinc. And it may be impractical for many countries to obtain a national diet that meets requirements with low quantities of ASFs. For example, Reina Engle-Stone showed that globally, as the percentage of energy from ASFs in national food supplies increases, micronutrient density and adequacy increase. In fact, the percentage of energy from ASFs needs to reach ~30–35% of energy for most nutrients to be in adequate supply nationally.
Christine Stewart highlighted that interventions to increase ASF consumption will have varying impact depending on the context. For example, the Lulun project in Ecuador, which provided an egg per child each day, had profound impacts on child growth whereas a similar trial in Malawi (the Mazira project) had no impact. This may have been due to (1) ASF consumption being much higher in Malawi, (2) the higher burden of infection and inflammation in Malawi and/or (3) because the base prevalence of stunting was much lower in Malawi than Ecuador.
In many developing countries, like Ethiopia, ASFs are increasing in price relative to staples. Derek Headey showed the vast regional differences in price (relative to the cheapest cereal) between dairy, eggs, white meat, red meat and fish. Interestingly, among these foods, red meat is the cheapest in Southeast Asia and India, by far the cheapest in sub-Saharan Africa, and the second cheapest in the rest of South Asia (after dairy). Of all regions, ASFs are least affordable in Sub-Saharan Africa.
How can programmes best reduce prices, increase access and improve safety of ASFs? By recognising the important role of markets, even in rural areas, resolving value chain bottlenecks like poor infrastructure, involving small-holders when it makes sense (sometimes more effective for dairy than poultry), increasing productivity of ASFs, reducing the cost of feed in Africa (particularly for poultry) and improving trade policies. Steven Staal highlighted the importance of traditional (informal) markets in developing countries, where 80–90% of livestock products are sold; that domestic markets dominate; and that demand for food quality and safety drives both formal and informal markets.
The second half was largely focused on the environmental impact and sustainability of ASF production. Importantly, it was noted that aquaculture has recently overtaken wild fishing globally as the primary method of seafood production, yet little is understood about the environmental implications of this transition. Aquatic systems and oceans are challenged by environmental changes, including acidification, lower oxygen levels, invasive species, disease and sea level rise.
Frank Mitloehner presented on the environmental impacts of livestock production. Interestingly, Americans eat the same amount of red meat or beef today as they did in 1909, but chicken consumption has skyrocketed in the past few decades. There are ~1 billion cows globally, nearly one third of which live in India. A major theme with beef and dairy production was that, to be sustainable, production efficiency in low- and middle-income countries needs to catch up with that of high-income countries, like the United States. But investment in ASF production research is dwarfed by investment in plant crops. Mitloehner also suggested that, globally, two thirds of agricultural land is marginal and could not viably produce crops. Using ruminants to produce high-quality ASFs on these lands while maintaining the ecosystems makes a lot of sense.
Sara Place made the point that because cattle consume mostly non-human-edible feed (e.g. grass and crop residues), they actually produce more ASF (~2.5 times in the US) per unit human-edible feed (e.g. corn and soybeans). Moreover, improving crop residue quality through genetics could have huge environmental benefits, if, for example, rice straw could be fed to cattle rather than burned or left to decompose, like it currently is across much of Asia.