13 Jun Nutritional Prowess and Environmental Impact: Insight from two Global Studies on Milk Supply
Milk and dairy products are currently essential nutritional components of the global food system, providing rich sources of human-consumable nutrients that address nutritional challenges. However, concerns have been raised by the scientific community about the impact of dairy production on greenhouse gas emissions and other environmental issues. In this context, a recent study published in the Journal of Dairy Science aimed to evaluate global contributions of milk to human food and nutrient supplies, greenhouse gas emissions, and water withdrawal. This paper overlaps with previous SNi research, but using a slightly different approach.
Using data from the United Nations Food and Agriculture Organization, the authors found that milk is a significant source of human-consumable vitamins A, B2 (riboflavin), B12, and calcium globally, contributing to over 10 % of the total available supply. Specifically, they found that milk provides 35% of the global calcium available for human consumption. It also supplies 24 % of vitamin B2 (riboflavin), approximately 36 % of vitamin B12, and about 10 % of available lysine, potassium, and phosphorus.
These findings differ somewhat from the previous results of the DELTA Model, which showed that milk accounts for 49 % of available calcium, 24 % of vitamin B2, 18 % of lysine, 22 % of vitamin B12, about 17 % of phosphorus, and 12 % of potassium. Some of the differences relate to the nutritional targets used: this study used US values where DELTA uses European targets. Key differences in nutritional targets are a higher US value for calcium and a lower US value for vitamin B12. The relative vitamin B12 contribution of dairy in this study is strengthened by the lack of accounting for the contribution of edible offal, which is the largest source of vitamin B12 in DELTA. For the essential amino acids, DELTA uses bioavailability adjusted values which leads to a higher weighting for animal sourced foods compared with plants.
Both studies confirm that milk ranks among the highest food items in terms of nutrient-to-calorie ratio for various amino acids, phosphorus, calcium, and riboflavin compared to other foods. Notably, milk is the largest contributing food item for calcium, lysine, phosphorus, choline, dietary fat, and vitamins A, B2, B12, and D. Despite its significant contribution to individual nutrients, milk only accounts for 5-7% of food energy availability, suggesting that its contribution to global nutrition does not necessitate high energy intake.
While both studies used similar publicly available databases for their data, differences exist in their approaches to assessing nutrient supplies and their focus on different aspects of the food system, as mentioned above. This study adopted a disaggregated approach, combining multiple data sources, including environmental impact data. The food waste fractions used are also different. It utilised a regionalised modelling framework to assess nutrient supplies in their pre-processed forms (e.g., fluid milk rather than processed dairy products; whole grains rather than bread) and environmental impacts associated with different supplies of milk and meat products at a more localised level.
Notably, the study reveals conditional dependencies (probabilistic) between greenhouse gas emissions and ruminant milk and meat, indicating that changes in one variable can influence the other. However, no such dependencies were found between water withdrawal and milk production. The global production of ruminant-derived products also presents a trade-off in nutrient use and provision, with net increases or decreases in key nutrients depending on whether milk or all ruminant products are prioritised. The specific nutrients affected, and the direction of the change, depend on production practices and the type of ruminant product. However, it is important to interpret these findings with caution, as probabilistic relationships do not necessarily imply causation. They describe the statistical associations between variables based on specific data and assumptions, but emphasise that there is not a simple linear relationship between production and environmental impact.
In summary, both studies highlight the importance of milk as a significant source of critical nutrients for the global population. The inclusion of environmental impact assessment expands the analysis beyond nutrition, highlighting the interconnectedness of nutrition and environmental sustainability. It provides insights into the environmental consequences associated with different food supplies. The combination of these perspectives offers a more nuanced and holistic understanding of global nutrition, allowing for identifying regional variations and developing solutions that optimise both nutrition and sustainability outcomes. This ultimately contributes to more effective strategies for improving nutrition worldwide. Moreover, the study cautions against reducing milk production solely to lower greenhouse gas emissions, as such an approach could have adverse consequences for the global supply of essential nutrients, including amino acids, vitamin A, vitamin B2, riboflavin, and arachidonic acid. Instead, better alternatives involve adopting on-farm approaches such as effective manure management, feed optimization, and genetic selection to mitigate the environmental impact of dairy farming while safeguarding the sustainability and availability of this food source.
This Thought for Food was written by Ejovi Abafe, a PhD Fellow in the SNi® team.
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