Whats more, demand for animal products in developing countries is growing so fast that meeting it will require an extra 300 million tons of grain a year by 2050.
【分析】本句为复合句，主架为 demand is growing so fast that。Whats more为插入语。that by 2050为结果状语从句，其中meeting it为现在分词短语作主语。
【译文】此外，发展中国家对动物制品的需求上升很快，要满足这些需求，需要在2050年之前每年增加3亿吨谷粮。