Starting fasting with exercise accelerates shift to fat-burning ketosis
Exercising at just about any time could be expected to benefit our well-being, and research has shown how when combined with fasting it can produce some surprising effects, such as supercharging the body's cellular disposal unit. A new study has explored how physical activity at the outset of a fasting period can accelerate a shift to ketosis, a metabolic state associated with the burning of stored fats.
Fasting diets in their various forms have received much fanfare of late on the back of the perceived benefits for our health. In recent years, studies have continued to shed light on the many ways fasting can influence the human body, including potentially boosting long-term memory, increase the efficacy of cancer treatments and improve liver health. Others suggest common forms of fasting are ineffective for the purposes of weight loss and other dietary regimes might be a safer bet.
In any case, our understanding of fasting continues to deepen as studies broaden our knowledge of its impacts on metabolism. The idea is that as our bodies are starved of food, they are starved of their ideal source of fuel – glucose. This sees the body turn to fat stores for energy instead, breaking them down and producing chemicals called ketones as a result. This metabolic state is known as ketosis.
“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,” says Brigham Young University (BYU) Ph.D. student Landon Deru, who led the study.
To zero in on this intersection of exercise, fasting and the human metabolism, Deru and his colleagues enlisted 20 healthy adults and tasked them with completing two 36-hour fasts following a standard meal. The first fast took place without any exercise involved whatsoever, while the second fast saw the participants complete a challenging 45- to 50-minute treadmill workout at the outset.
The scientists observed a big difference between the two. When the fasting period began with the treadmill exercise, the participants reached a state of ketosis on average three and half hours earlier and produced 43 percent more B-hydroxybutyrate, a ketone-like chemical. This is likely due to the workout rapidly burning through the body's glucose stocks, with the participants reaching ketosis around 20 to 24 hours into the fast without the help of exercise.
“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,” says study coauthor 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.”
While a useful addition to our knowledge around fasting, exercise and metabolism, there are still considerable blanks the researchers would like to fill in. They note that eating a big meal rather than a standard one before fasting is likely to negate the benefits observed in this study and prevent the body reaching ketosis for days. There are also questions around what constitutes the ideal fasting diet, and what the ideal amount of exercise might be for each individual.
"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," says Bailey. "But for most people it’s perfectly safe and healthy to fast once or even twice a week for 24 or more hours.”
And this is an important distinction, as this type of intermittent fasting that triggers switching between metabolic states stands apart from diets designed to place the body in a long-term state of ketosis. These ketogenic diets consisting of strictly high-fat foods that are low in carbohydrates and sugars may reduce body weight by burning stored fats, but can invite a broad range of other health risks according to recent research, with some experts even labeling them a "disease-promoting disaster."
With regards to this latest study, the scientists also note that the aerobic exercise at the start of the fasting period had no effect on the subjects' mood, hunger, thirst or insulin levels.
“Everyone’s going to be a little grumpier when they fast, but we found that you aren’t going to feel worse with the intervention of exercise – with exercise, you can get these extra benefits and be the exact same amount of grumpy as you would be if you didn’t exercise,” says Deru.
The research was published in the journal Medicine & Science in Sports & Exercise.
Source: Brigham Young University