"People can criticize me all they want, but the bottom line is it's science and the science is there — and (keto) is bad for your overall health and wellness,'' she said.
The ratio of fat to carbs and protein is 4:1 in the keto diet, with a goal of burning fat for energy rather than carbohydrates in order to lose weight.
He also defended the diet on TODAY at the time.
"My point is, what works for you, works for you,'' he said. "There's science on both sides that says it's not a great idea and science that says it is a great idea.
"I think it's up to people, with their doctor, with their medical professional (to make their own decision)."
TODAY co-anchor Savannah Guthrie also gave the diet a shot last year before ultimately deciding to stop, telling Dr. Mehmet Oz that while her mind was sharper, she had less energy.
She also remarked about the side effect of bad breath, as Dr. Oz said your breath can smell like acetone when you're in ketosis.
Michaels, 45, is still not buying the diet as a worthwhile pursuit.
"It attacks the s--- out of your liver, your thyroid,'' she said. "It shortens your telomeres, it’s bad for your macromolecules. I mean, it makes you stink, but we can table that one!"
She also feels the diet can be dangerous.
"Ketosis is a state of medical emergency, so when the body becomes what is called 'ketotic,' your cells cannot function,'' she said. "Your cells function optimally in a very specific pH. Any endocrinologist will explain this to you."
In her mind, the diet is more about people making money off it than helping improve people's health.
"What you also have to understand is that keto is a very big business,'' she said. "You've got billion-dollar corporations dumping money into this diet. When you see comments (about keto) and things like that on Facebook, a lot of time they're just bots. I promise you it's not good for you and there's better ways of doing this."
Michaels espouses eating a balanced diet with lean protein and fresh produce rather than the high-fat, low-carb ratio called for by the keto diet.
"Here's the thing, we can accomplish (all) of those things: weight loss, fat loss, reversing disease, without going into ketosis,'' she said. "How do I know? I've been doing it for thousands of people for three decades now. You can achieve all the good stuff with none of the bad stuff."