Dear Dr Adam,
I travel a lot with work which often derails my attempts at consistently intermittent fasting. Is there any data to show that inconsistently fasting would have adverse effects?
This is an interesting one.
Part of the beauty of intermittent fasting is by nature it allows for diet freedom. It has a lot of value as a method for maintaining body composition, say post-diet, because it’s a strategy rather than strict dietary guidelines. By nature, it has periods of control and periods of uncontrol, and so you’d hope that intermittent fasting, intermittently wouldn’t have any adverse effects.
And my first thought would be that no, it doesn’t have any ill effects because intermittent fasting in any form is going to have some benefits, of which you can learn plenty about in the email short course I put together for Form.
Let’s take the most popular forms of intermittent fasting as our examples, 16:8, where you consume your food within an eight-hour window in the day and abstain for the remaining 16, and 5:2, where you eat what you like for 5 of the 7 days in the week and dramatically restrict calories for the remainder.
Doing 5:2, where you’re effectively going through a 32 hour period of severe energy restriction, I don’t think there is going to be any issues in doing this type of fast for three or four weeks and then missing one.
Where you might hit a stumbling block is with the sort of grace period attached to the 16:8 method. To abide by this eating pattern, there’s likely to be a few weeks of entrainment, so going back and forth between doing it and not doing it will likely mean you struggle to fall back into the pattern.
But that said, you can probably re-entrain yourself over the course of several days, so it shouldn’t be all that hard to get back on track. And really, any adverse effects, as far as I’m aware, haven’t been looked at in any depth.
My feeling is that because it’s a diet strategy, rather than a strict nutrition plan, there shouldn’t be any metabolic changes caused wholesale by stopping here and there. Yes, you get spontaneous behavioural changes amongst people on 16:8 and 5:2 strategies alike – even people who indulge for five days on 5:2 don’t overeat so much to overcompensate for the two days of fasting. But it’s only one of many strategies to help fulfil a certain goal.
As a mindset, though, intermittent fasting is great – it entrains you to have natural compensation. You can have a big blow-out one day and naturally compensate in the subsequent days. If you can take any part of that mindset with you when you’re travelling and not able to stick strictly to your given eating windows, it can really only be of benefit.
For more insights from Dr Adam Collins on Intermittent Fasting, sign up to his email short course here.
A qualified nutritionist for 20 years, Dr. Collins holds an MSc in Nutrition & Metabolism and a PhD focusing on energy expenditure and body composition. He is Director of MSc and BSc Nutrition at the University of Surrey. His research interests lie in exercise nutrition, body composition and energy metabolism and current research includes exercise intensity, intermittent fasting and timing of food around exercise.
To have your nutrition questions answered by Dr Adam Collins, please email [email protected]