Mets first baseman Lucas Duda and Phillies manager Ryne Sandberg believe they know the reason for their recent food-poisoning bouts: tainted Shake Shack burgers.

Sandberg told reporters Tuesday that he lost six pounds in three days after eating a hamburger from the popular eatery at Citi Field.

"A couple of coaches took a bite and didn't like what they saw and threw the rest away," Sandberg said. "I was in a rush, so I ended up putting it away. I had one piece of toast in two days, and I'm feeling fine about that. I don't want anything in my stomach."

A Mets spokesman said Duda's burger was from a Shake Shack -- but not the one at Citi Field. Duda was hospitalized on Friday with an upset stomach. He played Saturday.

Greg Waters, Shake Shack's senior manager of marketing and communications, defended the burger chain's product.

"We've served thousands of guests at our Citi Field Shack over the past week, and this is the first we've heard of any issue whatsoever," Waters wrote in an email to Newsday. "We take every guest concern of any sort seriously, and as such reached out to Ryne Sandberg to get more information since we have not heard from him. We stand by our food quality 100 percent."