Not sure if you should work out on fasting days?
And if exercise will increase your hunger and cause you to cheat on your fast? Or whether the time of day that you work out will make a difference?
These are all important questions to us intermittent fasters. The last thing I feel like doing is too much exercise so that I overeat and undo the benefits of my fasts. That sounds about as much fun as running a marathon backwards.
If you’ve read our previous article about how chronic cardio exercise can increase appetite and cravings for high calorie foods, I’m sure you’ll be interested to know whether you’re doing the right thing by adding exercise to your fasting schedule. Thankfully Krista Varady looked at the effect of mixing exercise and intermittent fasting on weight loss in a recent study and has answered these questions for us.
If you watched the documentary ‘Eat, Fast and Live Longer’, Krista Varady was interviewed about her study where the participants fasted every second day (Alternate Day Fasting or ADF) by only eating 25% of their daily calorie needs on their fasting days (similar to the 5:2 method).
She found that the subjects did not overcompensate for these calories by overeating on their non-fasting days so they managed to lose weight successfully. And in this study they looked at ADF again but added exercise into the mix, to see what happens.
They split 64 men and women into four groups:
- One fasted as well (ADF) as well doing exercise
- One group only fasted.
- One group only did exercise
- And the last group did nothing at all.
The exercisers did 25 minutes of moderate exercise on a stationary bike or elliptical machine three times per week and gradually increased to 40 minutes per session over the 12 week study.
They asked them to rate the following factors:
- How hungry they felt after exercising and for the rest of the day.
- How full they felt after their fasting meal.
- How satisfied they felt after eating.
- Their level of ‘restrained eating’ (the conscious restriction of calories in order to lose weight).
- Their level of ‘uncontrolled eating’ (their tendency to eat more than usual due to a loss of control).
- The amount of ’emotional eating’ (eating when not hungry for emotional reasons).
- They also took note of what they all ate on their non-fasting days.
What Did They Find?
There was no difference in appetite in the fasting with exercise group regardless of whether they exercised on a fast day or a non-fast day. There was also no increase in the urge to cheat on a fast day if they chose to work out on that day.
The amount of ’emotional eating’ decreased in the fasting with exercise group. However there was no difference in hunger, satisfaction and fullness in the fasting with exercise group. Strangely these all improved in the group that only fasted (with no exercise) which was a very interesting discovery.
In summary they found that with ‘moderate level’ cardio for up to 40 minutes:
- You can work out on a fast day and it’s not likely to lead to overeating.
- Your hunger should not increase if you work out on a fast day.
- Your feeling of fullness after eating should not decrease if you work on a fast day.
- Your feeling of satisfaction after eating should not decrease if you work on a fast day.
- Your level of ‘restrained eating’ and self control around food should improve!
- The amount of uncontrolled eating (binge eating) and emotional eating should also improve!
- There should be no difference and time of day you exercised and the amount of food consumed on that day.
So In Summary…
This was an interesting study because all of the benefits mentioned above also applied to the group who only fasted and did no exercise at all. Not only that, but the fasting only group also had a reduction in hunger and an increase in satisfaction and fullness and the exercise group did not!
I should also mention that aside from these benefits in ‘eating behaviours’ the study showed the fasting with exercise group had a higher rate of weight loss than the ADF-only group that did not exercise, but only by 7%. So it seems intermittent fasting and working out only has a small advantage over intermittent fasting without exercise.
So I guess the take home point is that if you do choose to add exercise to your fasting schedule (and obviously I recommend that you do for the other health benefits) you’ll probably lose weight fast but keep an eye on how much exercise you do and whether it changes your eating habits. Otherwise you could be undoing the 7% benefit that it has over intermittent fasting without exercise.
Remember, the exercise in this study was only done three days a week and would not be classed as heavy exercise and can be replicated with by other activities such as fast paced walking cycling, playing golf, swimming etc. They estimated the calories burned in each exercise session to be around 150–250 calories, so keep that in mind when planning your workouts.
My advice is to keep a food diary for the first two weeks of a new exercise regimen so you can look over your eating habits and see if there are any changes and adjust your workouts accordingly.
What has your experience been with exercising on fast days? And what type of exercise do you usually do? We’d love to hear your comments below!