Katie Couric is the latest celebrity to publicly sing the praises of the Keto diet, which generally calls for eliminating sugar and grains, eating low carb, moderating protein, and piling on the good fats. However, she also experienced a common side effect right after she kicked it off.

"So I've been doing the keto diet for a week now and I actually do feel better," the journalist posted on Instagram Stories. "The fourth or fifth day, I felt a little shaky and headachy, but I feel much better."

Women's Health recognizes these symptoms as being part of what is commonly known as the "Keto flu," as people transition from burning fat instead of carbs for energy, which puts the body in a state of ketosis. 

Katie also shared her new food and beverage routine so far on social media.

"I'm eating mostly protein and some cheese," she wrote. "And I'm putting half-and-half in my iced coffee, and I gotta tell ya, it's damn good."