Background on me: Male/5’11”/Starting Weight: 250lb/Current Weight: 235 lbs; doing the 16:8 method and my fasting window is from 10pm-2pm (I eat from 2pm-10pm).
I was enjoying a snack the other night pretty close to when my fasting window started (I believe I finished eating it at 9:50) and I thought to myself, “If I eat this close to my fasting window, wouldn’t I technically be breaking my fast since digestion takes time?” I turned to google for answers but none of the articles/blogs I found really answered that question directly or they provided the infamous “technically yes, but no” answer that a lot of IF sources give. So, I figured I’d pose the question here and get a little discussion thread going.
My personal opinion is yes, eating within 30-40min before your fasting window officially begins will break your fast; or at least dampen the positive effects of IF such as higher energy, suppressed hunger, and efficient/optimal autophagy. I’ve always been really bad at measuring the effectiveness of IF aside from fat loss/weight loss so I wouldn’t even know how to figure out if the mentioned effects are even being affected, but from what I’ve read thus far about IF I’m making an educated guess as to what is actually happening.
After consulting the Cleveland Clinic about digestion (https://health.clevelandclinic.org/how-long-does-it-take-to-digest-food/) I think it is safe to assume that, without accounting for the time food remains in your small intestine, the time it takes to digest solid foods is anywhere from 30-120min and 10-60min for liquids depending on the how complex the carb-chains are and various body factors such as weight, age, and medications you take (essentially digestion time is different for everyone based on key variables).
Therefore, given the digestion time lengths listed above, if I eat an apple 10min before my fasting window begins, then my body will still be digesting that apple well beyond the start of my fasting window. Hypothetically, this would be breaking my fast.
Again, I have no conclusive evidence that this is the case. I just think it is a neat discussion topic, especially if we can get any nutritionists in this community to give their input.
The described duration of the fasting window (particularly the ‘minimum’ 16:8 for bonus effects) already accounts for this. All this thinking has already been done and applied, the numbers literally describe the time during which you can swallow food and the time during which you cannot.
To me, that’s the major point of setting an eating window. You have a cutoff to allow your body time to digest, and then get into the extra benefits.
Perhaps I’m naive or misinformed, but my fasting app tells me, based on when I start fasting, what stage I am currently in. I presume these calculations assume that I ate right up until the time I told it I was specifically NOT eating, and takes that into account. I don’t expect that it’s 100% accurate, as it doesn’t know my specific metabolism and how quickly I digest, but it’s giving me the general idea based on averages.
If you’re really concerned that you’re actually hitting something like increased autophagy, which my tracker says I hit about 18 hours after starting my fast, (and which I’ve seen from various sources start anywhere between 16 and 24 hours) then you might do well to tighten your eating window. I don’t go below 19 hours of fasting, and more often than not I’m at 22 hours of fasting. This way I am pretty confident that I’m getting at least an hour of increased autophagy (and realistically, my body is performing it before then because I’m not eating, it’s just ramped up by then.) It’s why I’ve never gone for a 16 hour fast, because it’s right on the cusp, if you even hit it at all.
Like, I want to try to hit increased autophagy most days (let’s just say there’s enough illness in my family tree to be pretty confident that I’m at risk for some not pleasant things) but I’m not obsessed about hitting it every day. Pretty sure that the other benefits of IF (calorie reduction/losing weight and not eating crap, which is critical for me in sustaining my fasts) are going to have plenty of positive impact on my chances.