The keto diet will likely be a popular choice for people looking to burn body fat now that Thanksgiving is in the rearview mirror. But the time it takes to get into ketosis can be discouraging. Researchers at Brigham Young University found a short cut when they discovered people who began a fast with exercise were able to reach ketosis 3.5 hours faster than those who did not exercise.
Ketosis occurs when the body uses up its available glucose and begins breaking down stored fat for fuel. The body produces ketones during ketosis which is a healthy energy source for the brain and heart and is thought to combat diseases like diabetes, cancer and Parkinson’s.
It normally takes between 20-24 hours for a healthy adult to reach ketosis on their own during a fast but researchers at BYU were looking for ways to speed up that process.
"We really wanted to see if we could change the metabolism during the fast through exercise, especially how quickly the body enters ketosis and makes ketones," said researcher Landon Deru.
Deru and others worked with 20 healthy adults for the study. They completed two 36-hour fasts while undergoing tests every two hours when awake to assess their hunger and mood as well as their levels of B-hydroxybutyrate (BHB), a ketone-like chemical.
The sessions began with a standardized meal. The first fast began without any exercise and the second started with a challenging treadmill workout.
Those who exercised reached ketosis 3.5 hours quicker and produced 43 percent more BHB. Researchers theorize it’s because the exercise caused them to burn up the available glucose quicker which led to a faster transition to ketosis.
"For me, the toughest time for fasting is that period between 20 and 24 hours, so if I can do something to stop fasting before 24 hours and get the same health outcomes, that's beneficial," said Bruce Bailey, a BYU exercise science professor. "Or if I do fast for my usual 24 hours but start with exercise, I'll get even more benefits."
Bailey qualified that statement by saying, "If you carb load or eat a huge meal before you fast, you may not reach ketosis for days, even if you do exercise, so you should eat moderately before fasting," he said. "We also don't know the ideal frequency for fasting. There are definitely certain people who shouldn't fast, such as those with Type 1 diabetes, and obviously it's detrimental to fast 24/7. But for most people it's perfectly safe and healthy to fast once or even twice a week for 24 or more hours."
The study participants ran for an average of 45-50 minutes on the treadmill but researchers were not looking to establish the optimal amount or type of exercise. The thought was the more energy a person can burn, the better.
"You can get a pretty good estimation of how many calories you're burning in most exercises, and the more carbohydrates you burn off (without overdoing it or injuring yourself), the better you set the stage for starting ketosis early in your fast," Deru said.
Click here to read more in the journal Medicine & Science in Sports & Exercise.