A man on a quest to find the best diet tried eating ultra-processed foods for a month. He quit after five days.

Gavin Wren/Getty

• Gavin Wren, a food policy expert, challenges himself to eat a different diet every month.
• He tried eating only ultra-processed foods but gave up after five days.
• He told Business Insider that the diet made him feel "sluggish" and gave him a low mood.

A food policy expert who challenged himself to eat only ultra-processed foods for a month...