In recent decades there has been a sustained and substantial shift in human diets across the globe towards including more livestock-derived foods. Continuing debates scrutinize how these dietary shifts affect human health, the natural environment, and livelihoods. However, amidst these debates there remain unanswered questions about how demand for livestock-derived foods may evolve over the upcoming decades for a range of scenarios for key drivers of change including human population, income, and consumer preferences. Future trends in human population and income in our scenarios were sourced from three of the shared socioeconomic pathways. We used scenario-based modeling to show that average protein demand for red meat (beef, sheep, goats, and pork), poultry, dairy milk, and eggs across the globe would increase by 14% per person and 38% in total between the year 2020 and the year 2050 if trends in income and population continue along a mid-range trajectory. The fastest per person rates of increase were 49% in South Asia and 55% in sub-Saharan Africa. We show that per person demand for red meat in high-income countries would decline by 2.8% if income elasticities of demand (a partial proxy for consumer preferences, based on the responsiveness of demand to income changes) in high-income countries decline by 100% by 2050 under a mid-range trajectory for per person income growth, compared to their current trajectory. Prices are an important driver of demand, and our results demonstrate that the result of a decline in red meat demand in high-income countries is strongly related to rising red meat prices, as projected by our scenario-based modeling. If the decline in the income elasticity of demand occurred in all countries rather than only in high-income countries, then per person red meat demand in high-income countries would actually increase in 2050 by 8.9% because the income elasticity-driven decline in global demand reduces prices, and the effect of lower prices outweighs the effect of a decline in the income elasticity of demand. Our results demonstrate the importance of interactions between income, prices, and the income elasticity of demand in projecting future demand for livestock-derived foods. We complement the existing literature on food systems and global change by providing quantitative evidence about the possible space for the future demand of livestock-derived foods, which has important implications for human health and the natural environment.

近几十年来，全球人类饮食发生了持续和实质性的转变，以包括更多的牲畜衍生食品。持续的辩论仔细审查这些饮食变化如何影响人类健康、自然环境和生计。然而，在这些辩论中，关于在未来几十年中，在人口、收入和消费者偏好等一系列关键变化驱动因素的情况下，对牲畜源性食品的需求可能会如何演变，这些问题仍未得到解答。在我们的情景中，人口和收入的未来趋势来自三个共享的社会经济途径。我们使用基于场景的模型来显示红肉（牛肉、绵羊、山羊和猪肉）、家禽、牛奶、如果收入和人口的趋势继续沿着中等轨迹发展，那么在 2020 年到 2050 年间，全球人均鸡蛋数量将增加 14%，总量将增加 38%。人均增长率最快的是南亚的 49% 和撒哈拉以南非洲的 55%。我们表明，如果高收入国家的需求收入弹性（消费者偏好的部分代理，基于需求对收入变化的响应）下降 100，高收入国家对红肉的人均需求将下降 2.8%与目前的轨迹相比，到 2050 年人均收入增长处于中等轨迹的百分比。价格是需求的重要驱动因素，我们的结果表明，高收入国家红肉需求下降的结果与红肉价格上涨密切相关，正如我们基于场景的建模所预测的那样。如果需求的收入弹性下降发生在所有国家而不是仅发生在高收入国家，那么高收入国家的人均红肉需求在 2050 年实际上将增长 8.9%，因为收入弹性驱动的全球收入下降需求降低了价格，价格下降的影响超过了需求收入弹性下降的影响。我们的结果证明了收入、价格和需求收入弹性之间的相互作用在预测未来对牲畜源食品的需求方面的重要性。我们通过提供有关未来牲畜源性食品需求可能空间的定量证据，补充了有关粮食系统和全球变化的现有文献，