Confused about the meat/milk/diet wars? That’s OK. It’s complicated. And poorly fact-checked. And under-studied.

All illustrations by Japanese graphic artist Zenji Funabashi.

Just in time to add fuel to the fire of the current meat, milk and diet wars being waged in scholarly and lay media alike comes the latest issue (Oct 2019) of the scientific journal Animal Frontiers on Foods of animal origin: A prescription for global health, with the term ‘health’, here, covering both human and environmental health.
For readers attending to the ongoing storm of polarized arguments, accusations and evidence about the health risks or benefits of eating meat, alt-meats and other ‘real’ and ‘alternative’ livestock-derived foods, this article may not offer safe harbour.
What it does offer, however, is valuable—a clear-headed, evidenced based, balanced look at the facts as we know them, and the facts that we need. One message that comes through loudest is that we just don’t have the evidence needed to make definitive statements on any sides of the global livestock debate.
Consider, for example, this paper in this issue, on The role of livestock products for nutrition in the first 1,000 days of life, written by three scientists at the International Livestock Research Institute (ILRI) and focusing on the available evidence for the roles consumption of livestock-derived foods play in the first 1,000 days of life.
The paper starts off conventionally for a development-oriented paper by noting that diets of most people in low- and middle-income countries remain nutritionally inadequate, leading to the world’s highest levels of undernutrition, especially among children.

Poor people in poor countries often subsist on suboptimal diets based on cheap staples and have limited access to nutrient-dense foods such as pulses, fruit, or meat . . . As a result of these circumstances, individuals do not receive sufficient nutrient intakes to sustain optimal well-being.

The common reality in Africa, say the authors, is that milk, meat and eggs, while highly nourishing are also relatively dear, and so are uncommon foods for young children in poor households.
The authors then note that while ‘a shift from food security (access to enough food) to nutrition security (access to enough nutritious food) has prompted the development of interventions to increase nutrient intake’ such as by fortifying food with nutrients, ‘[l]ittle attention has been given . . . to the specific role of . . . meat, milk, and eggs (and their derived products) on nutrition and their potential to help achieve nutrition security goals.’
One factor not helping to redress this odd neglect, they suggest, is that ‘Media outlets in recent years, primarily in high-income countries, have increasingly been flooded with reports that are critical of the role of meat, in particular, and livestock-derived foods (e.g., milk and eggs), in general, as part of diets. Their environmental footprint, as well as their suggested negative effects on health, are ostensible arguments used to promote a shift to diets containing little to no animal-sourced foods. . . .’
The remedy for this, imply the authors, is staring us in the face in the manner of all the farm animals populating most poor countries, where ‘it would represent a significant missed opportunity to not harvest livestock-derived food products to optimize the nutrition of the most vulnerable. . . .’

This might seem to be an understatement with all the benefits meat, milk, offal and eggs provide to human nutrition, which they go on to cite at length.

Livestock-derived foods possess a specific nutrient composition that matches well the human body’s needs, particularly during the critical first 1,000 d of life covering the period from conception through pregnancy up to 2 yr of age . . . . Livestock-derived foods could have an important role in reducing stunting and some key micronutrient deficiencies. Indeed, eggs, milk, meat, and offal are all nutrient-dense food products that contain high-quality proteins and several highly bioavailable vitamins (e.g., vitamin B12, only available in foods of animal origin, preformed vitamin A, and vitamin D) and minerals (e.g., iron, zinc, and calcium). Animal-source foods provide these nutrients at sufficient levels and with a great degree of digestibility, what makes them particularly adequate for young children as well as pregnant and lactating women who are in stages of rapid growth and development and have high micronutrient requirements but small intake volumes . . . .

Animal protein is a high quality, easily digested protein that possesses a high biological value, which is conducive for greater net protein utilization compared with nonanimal proteins. Animal proteins have a more balanced essential amino-acid profile relative to human tissues . . . . In addition, different studies have found that intake of milk and meat can have positive effects on nutrition and functional outcomes such as cognitive development, . . . For all these reasons, livestock-derived foods can be interesting targets for interventions to reduce the biological impact of malnutrition, including poor growth or micronutrient deficiencies.

But the authors go on to caution that ‘The scientific literature reveals a relatively large body of literature confirming the link between intake of livestock products and positive nutritional outcomes. The majority of this evidence is however derived from observational studies, which cannot prove a “causal link” exists between intake and the observed improvement in nutritional indicators. . . .’
In particular, they say, regarding the main topic of their paper, ”There is a significant dearth of scientific information examining the impact and trade-off of livestock-derived food consumption during the first 1,000 days of life in poor populations. . . .’
First they note the importance of livestock-derived and other nutrient-rich diets for pregnant women and their infants: ‘Adequate quantity and quality of nutrients are necessary for the period of time from conception, through pregnancy, and up to 2 years of age for individuals to not only survive, but to thrive throughout life . . . . The potential impact of consuming nutrient-rich livestock products at this age is of utmost importance for adequate development, especially in contexts were diets are little diverse and nutrient poor. . . .’

But, but, but, they say, the evidence, while pointing to the importance of these foods, is still relatively weak.

Randomized control trials relative to the impact livestock products have on the first 2 years of life are also limited. The scarce literature seems to suggest that, at these early stages of life, intake of milk is particularly important for linear growth. One of the largest randomized control trials conducted to date showed that toddlers in rural areas of Kenya whose diets were supplemented with cow’s milk grew taller than children consuming the usual diet or a diet supplemented with beef . . . .

A very recent study in Ecuador . . . showed that supplementing nutrient-scarce diets of children 3 to 9 mo of age with one egg per day for 6 mo increased child height. The study also found increased concentrations of essential micronutrients in the plasma and the prevalence of stunting was reduced by 47% in the egg-supplemented children compared with children on the traditional diet. On the other hand, in a study in rural Malawi, provision of 1 egg per day to children had no overall effect on linear growth.

A reason for such weak and conflicting evidence is a sound one.

Most studies however have weak designs which limit their capacity to accurately evaluate the impact of animal foods. Conducting research and, particularly randomized control trials, among these groups is particularly difficult due to stringent ethical considerations and health risks that make it challenging to design studies that will provide robust, sufficient scientific evidence.

Results obtained among school-aged children are generally positive and somewhat clearer, although ‘mixed’.

More research has been conducted targeting school-aged children, revealing results that are mixed. Several studies have recorded improvements in nutritional outcomes from diets supplemented with livestock products compared with the base diet. Milk is believed to improve linear growth in children (particularly in malnourished children), mediated by the stimulation of insulin-like growth factor . . . .

Consumption of livestock-derived foods has also shown positive impact on functional outcomes. For example, research looking at the effects of meat supplementation in children has suggested that consuming meat could improve cognitive development. The improvements in cognitive ability could be a result of meat providing a highly bioavailable source of the necessary combination of micronutrients that may have been missing or undersupplied by the traditional diet.

Meat and milk are among the few products that contain vitamin B12, which is a key element to support cognitive development. Also in this study, meat improved cognitive performance, school test performance, leadership behavior, and physical activity . . . . The influence of meat on cognitive development is thought to be related to greater intake of vitamin B12 and a more bioavailable source of iron and zinc. Together with high-quality protein, these may facilitate specific mechanisms such as the speed of information processing in learning tasks.

The authors then raise some of the non-nutritional aspects of livestock food consumption.

Globally, the livestock sector is one of the most important in terms of land-use, economic value, employment, and use of animals. Unsurprisingly, livestock production can have many impacts, both positive and negative, on societies and ecosystems beyond providing food. Livestock production brings a range of economic, societal, and environmental benefits . . . .

Most of those impacts are particularly important in low- and middle-income countries, where livestock production is the primary source of income and livelihoods for many families, especially in rural areas.

And then the authors lower the boom on the several ‘existential threats’ livestock systems pose in poor countries.

Although this paper focuses on the nutritional benefits of livestock products in the first 1,000 days of life, a balanced discussion must also pay attention to the negative impacts associated with livestock production. Unsurprisingly, these are the issues that have received most attention over the past decades.

The authors focus on four livestock-related threats that, while not nutritional in nature themselves, can and could do large nutritional harm to the world’s poor. The first of these threats is a horrendously large, and as yet overlooked, burden of diseases caused by foods (often meat and milk) that are contaminated with bacteria and aflatoxins and other toxins—diseases that contribute significantly to the poor nutritional status of infants. A second threat is the spread of animal-to-human ‘zoonotic’ diseases, such as bird flu, which make up a staggering three-quarters of all new and emerging infectious diseases of people. The third threat is a climate catastrophe caused by global warming, with livestock systems estimating to generate 14.5% of anthropomorphic greenhouse gases today. And a fourth threat is that of poor animal welfare, which can be especially problematic and hard to address in the growing intensive livestock production systems of developing and emerging economies.
Foodborne disease

Although it is difficult to bring these issues to a common metric, it is likely that the impact of foodborne disease may have the highest ongoing burden, whereas the greatest potential for catastrophic loss (or existential risk) may stem from the contribution of livestock production to climate change and to the emergence of global pandemics.

The landmark first assessment of the global burden of foodborne disease . . .  conducted by the World Health Organization considered 31 food-related hazards. It concluded that foodborne disease has a health burden comparable to malaria, HIV/AIDS, or tuberculosis. Most of this burden (98%) falls on developing countries and 40% on children less than 5 yr of age. Although information on source attribution (that is, what foods are responsible) is weak, livestock products are disproportionately represented as causes of foodborne illness . . . .

Foodborne disease and health hazards found in livestock products (such as aflatoxins) may also directly contribute to poor nutritional status in infants in low- and middle-income countries. A 9-country study found that 25% of stunting could be attributed to experiencing more than four episodes of diarrhea before the age of 24 mo . . . .

Studies find a strong peak in diarrhea after the introduction of supplementary foods and find that weaning foods often have high levels of microbial contamination and adulteration . . . . Aflatoxins may directly contribute to stunting, and there are demonstrated associations between higher toxin levels in food and poorer growth in several contexts, including children consuming milk with aflatoxins in Kenya, although a causal relation is yet unproven.

Zoonotic disease

Livestock production, especially in intensive systems and if accompanied by land-use change, can lead to the emergence of zoonotic diseases  . . . . Around 75% of new and emerging human diseases (including many antimicrobial resistant organisms) are zoonotic . . . . These have the potential to sicken and kill large numbers of people and to damage economies. Emerging pandemics are considered to represent one of the few important risks to societal collapse.

Climate change crisis

Another existential threat to humanity is climate catastrophe, which, under the most extreme scenarios, could make large parts of the world uninhabitable. Although estimates vary, the livestock sector is made responsible for up to 14.5% of anthropogenic greenhouse gas emission . . . .

Livestock production also has implications for other planetary boundaries, notably biosphere integrity, freshwater consumption, land system change, and nitrogen and phosphorus flows . . . . Production of other foods, especially those requiring high levels of inputs and of low nutritional value (e.g., greenhouse grown, irrigated lettuce), also has environmental effects . . . .

Poor animal welfare

As well as environmental, there are important societal impacts of livestock production. Animal welfare is an increasing public concern raised by consumers, especially in high-income countries. Animal welfare conditions currently vary across countries and production systems, and depend on socio-economic and regulatory settings, as well as on religious and cultural traditions, consumer and civil society organizations pressure. However, animal welfare is often especially problematic in intensive systems of low- and middle-income countries. Other social consequences of intensification include rural abandonment, poor working conditions, low wages, vulnerability of migrant labor, and occupational hazards.

So where does that leave us?

While as yet under-investigated and by necessity weak in nature, recent evidence suggests that meat, milk, and eggs consumed during the first 1,000 days of life (from conception, through pregnancy, to two years of age) ‘can significantly improve an individual’s ability to thrive later in life.’ Evidence also suggests that adding modest amounts of meat, milk or eggs to the diets of under-nourished school-aged children supports their physical and mental growth, again with life-long benefits. On the other hand, the rising global demand for livestock-derived foods, while having great potential to advance many of the UN’s Sustainable Development Goals, including ending poverty, hunger, malnutrition and environmental degradation (topics covered in other papers in this issue; see, for example, Sustainable livestock systems to improve human health, nutrition, and economic status, led by ILRI scientist Padmakumar Varijakshapanicker; for an even broader evidenced-based review of the role of protein (meat and otherwise) in our future food supply, see the 2019 World Economic Forum-ILRI white paper on Meat: The Future Series—Options for the livestock sector in developing and emerging economies to 2030 and beyond), could, if inadequately addressed, lead to greater incidences of foodborne illness, zoonotic diseases, climate crises and animal harm.
Although I am loath to end yet another article on research with a ‘more research is needed’ plea, I fear that that is an inescapable conclusion. We don’t know enough and we ought to. Livestock issues sit at the nexus of some of our biggest global opportunities and challenges, and whether we lean towards meat-eating or vegetarianism, towards Northern or Southern diets, we will move the needle on neither the big opportunities nor the big challenges by continuing to neglect the livestock sector.
Read the whole paper, which includes links to referenced research papers, by Silvia Alonso, Paula Dominguez-Salas and Delia Grace, The role of livestock products for nutrition in the first 1,000 days of life, in Animal Frontiers, Vol 9, Issue 4, Oct 2019.
About the authors

Silvia Alonso is a senior scientist at the International Livestock Research Institute (ILRI), based in Addis Ababa, Ethiopia. She has more than 10 yr of experience in public health research, both in Europe and internationally, focusing on the impacts of livestock production on human health. Her current research explores how to leverage livestock value chains to improve health and nutrition. She is leading the first large-scale field trial of an intervention in informal markets to improve food safety and child nutrition in peri-urban Nairobi. She is a Diplomate of the European College of Veterinary Public Health and the Chair of the ethics IRB at ILRI. Contact her at s.alonso [at] cgiar.org
Paula Dominguez-Salas is a veterinarian and a public health nutritionist with a focus in developing countries. She now works as a human nutritionist to optimize the impact of livestock development programs at the International Livestock Research Institute (ILRI) in Nairobi, Kenya, and is assistant professor in nutrition-sensitive agriculture at the London School of Hygiene and Tropical Medicine, from where she also graduated. Her research interests are micronutrients, dietary practices, food safety, and gender. Her professional experience is mostly in East and West Africa and Latin America. Contact her at p.dominguez-salas [at] cgiar.org
Delia Grace is an epidemiologist and veterinarian with more than 20 yr’ experience in developing countries. She graduated from several leading universities and currently co-leads research on human and animal health at the International Livestock Research Institute (ILRI) based in Nairobi, Kenya. Her research interests include food safety, emerging diseases, gender studies, and animal welfare. Her career has spanned the private sector, field-level community development, and aid management. Her research program focuses on the design and promotion of risk-based approaches to food safety in livestock products. She is also a key player on ILRI’s Ecohealth/One health approach to the control of zoonotic emerging infectious diseases and agriculture-associated antimicrobial resistance. Contact her at d.grace [at] cgiar.org