I went on the Subway Diet for a week - and it's clear why the chain is no longer America's destination for healthy fast food

Kate TaylorHow much Subway can one person handle in a week?Subway has gone from the king of healthy fast food to a depressing punchline. But are the sandwiches to blame?

Given falling sales, the company has been trying to win over consumers with new menu items and all-natural adjustments like removing artificial colors, flavors, and preservatives from its US menu.

However, the sandwich chain faces ample competition in the form of fast-casual restaurants like Sweetgreen that offer locally sourced ingredients. Worse, the company faces the stigma from former spokesperson Jared Fogle's descent.

Looking at Subway's sales slump, I wondered if Fogle's diet plan holds up over time - or is it obsolete given the evolution of Americans' dietary preferences?

In a quest to find out, I decided to try one of the most (in)famous diet plans of the 21st century: The Subway Diet.