leaving nutritional deficiencies, especially in the form of periodic food shortages, as the most likely causative agents.

这是现在分词短语作补充性状语。现在分词leaving的逻辑主语为前面整个主句的内容。这个分词短语的作用类似于非限制性定语从句which leaves..., which 的先行词为主句内容。

leaving sth as sth. leaving在此为使役动词，意为使 A 成为 B, 使得营养不足成为最有可能的原因。as介词短语为leaving的宾语补足语。especially in the form of periodic food shortages 为介词短语作nutritional deficiencies的非限制性定语。有人会认为这是插入语，对nutritional deficiencies作补充解释。