You merely need to visit a western supermarket today to see that many people regard protein as some kind of universal elixir – one food companies are profitably adding to anything they can. 

one food companies are profitably adding to anything they can. 

= an elixir which food companies are profitably adding to anything that they can add it to.

one为名词替代词，= an elixir. 是前面的elixir的同位语，后接省略了关系代词that/which的定语从句。

anything=any food，其后的they can也是省略的that的定语从句。

can为操作词替代形式，即替代定语从句的谓语以及谓语的补足成分（宾语和状语）

译文：

你只需造访一下西方的超市，你就会明白许多人把蛋白质视为某种万能的灵丹妙药，食品公司把这种灵丹妙药加入他们能加的所有食物中，从中获取利润颇丰。