"I don't understand, like, why would anyone think this is a good idea?" Michaels says bluntly.
"'You know what we need to do? All fat and animal protein. Ding, Ding, Ding,'" she mocks creators of the diet. "No -- bad plan for a million reasons."
Michaels goes on to explain why she would never recommend the diet to anyone.
“Your cells, your macromolecules, are literally made up of protein, fat, carbohydrates, nucleic acids," she notes. "When you do not eat one of the three macronutrients -- those three things I just mentioned -- you’re starving yourselves. Those macronutrients serve a very important purpose for your overall health and wellbeing -- each and every one of them.”
The Biggest Loser trainer says there's no shortcut to cutting out processed sugar and processed grains and eating a well-rounded diet.
"To make a very long story short, avoid the keto diet," she says. "Common sense -- balanced diet is key."
“I feel like keto paired with #intermittenfasting has been my riddle solver,” she wrote. “I’ve officially weaned off my poison sugar free creamer and am now drinking black coffee with stevia and coconut oil.”
Of course, some stars are just genetically blessed. ET spoke to supermodel Heidi Klum last March, who insisted that while she eats "super healthy" in her day-to-day life, she doesn't "do anything diet."
"When I drink milk, I drink whole milk," she explained. "Or if I have a Coca-Cola, I drink real Coca-Cola. I don't do anything fat-free."