If you've tried fasting or are planning to do so, you're bound to run into at least some of the problems mentioned below. Based on my personal experience, they appear to some degree regardless of whether you're doing intermittent fasting or the occasional longer fast.
While these side effects of going without food may not be pleasant, the good news is that there are ways to deal with them. And, at the very least, knowing what they are beforehand helps you to prepare yourself mentally. Once you get acquainted with them, it becomes easier to detach yourself from them and to see them more objectively for what they really are: mere hurdles on the way to better health.
1. Feeling of hunger
This is the obvious one, of course. The feeling of hunger is the first effect to kick in once you stop eating. Depending on what and how much you ate prior to the fast, it may take anywhere between an hour and half a day before your stomach starts to growl again.
The key to tackling this problem is understanding how the feeling of hunger comes and goes during fasting. Many people who fast for several days at a time report that the hunger subsides after the first few days, after which the whole thing gets much easier. Thus, it may in fact be easier to do a 4-day fast once a month rather than a 2-day fast twice a month.
However, there is a definite hunger cycle noticeable even during one-day fasts (e.g. intermittent fasting or alternate-day feeding). I find that I usually experience my first hunger pang about 4 hours after the last meal. At this point, it's not even a feeling of needing more energy, it's just a slight craving to eat something, and thus pretty easy to ignore. Drinking something helps.
The cravings then disappear for many hours, and about 18 hours into the fast, a more serious hunger emerges. This is the point at which the temptation to break the fast is at its greatest. However, if you can force yourself to pull through, the hunger subsides after a few hours. Drinking coffee or tea is helpful; just don't forget to drink water also. Another efficient way is to find something else to think about. When you're concentrating on, say, your work or a hobby, you'll find that it's quite easy to go through this phase, and it's smooth sailing from there on again.
2. Fatique and brain fog
Well, almost smooth. With the disappearance of hunger comes a new hurdle: physical fatique and brain fog. At this point, the idea of eating seems appealing not so much because of cravings but because you find your energy reserves temporarily depleted. Sitting on a chair and staring at the wall seems like a strenous exercise. You can forget solving complex mathematical problems during this time.
As with hunger, the key is to know that these negative effects will pass. In fact, they will pass even more quickly than the hunger. I find that during a 24-hour fast, the brain fog and fatique start to subside after an hour or so. While focusing on something else is a good way to skip through the hunger phases, it's very difficult to focus on anything during the brain fog phase. Hence, I just tend to wait them out, staring at the cubicle wall in my fasting-induced trance. Trying to lift the fog with a couple of shots of espresso is... interesting. But don't take my word for it, try it for yourself.
A note about dry fasting (which is going without food and water): the fatique and brain fog phase seems to last much longer with dry fasts than normal fasts. Though you may go into ketosis quicker with this method, be prepared to endure some hours of fatique before the switch happens. I did not find any good way to get around this during my dry fast experiment.
3. Dry mouth
I must admit I haven't read that many reports about this particular difficulty from other fasters, but I frequently notice it myself. The obvious solution is of course to drink more water. It does indeed help, but I find that a dry mouth during fasting is not only related to drinking water but also to the lack of food itself. That is, no matter how much water you drink (and if you're not eating, most of it will just flush out quickly), the feeling of a dry mouth may persist. Still, the problem can be minimized with enough hydration.
My suspicion is that the lack of nutrients during fasting may explain this phenomenon; for example, on some days taking a magnesium supplement seems to help, and eating something even without drinking (after the fast, of course) often gets rid of the problem. Whether it's really related to dehydration at some level, I don't know. Tea and coffee are good ways to boost energy levels while on an empty stomach, but keep in mind that they also make the dry mouth worse. This can be relieved by drinking a glass of water for every cup of coffee or tea.
During dry fasting, this was a major problem for me. While it's easy to tell yourself that going without food is good for you and that the hunger will pass soon enough, it's much more difficult to do the same with water. Even half a glass seems so tempting that it takes quite a bit of willpower to endure the thirst and dehydration.
4. Sensitivity to cold
An increased sensitivity to cold is a common problem with those who practice (chronic) calorie restriction, but the "less energy, less body heat" rule applies to fasting as well. However, in the case of short-term fasts, the effect is only temporary. During the first 12 hours of the fast, nothing really significant happens, but from there on, the sensitivity to cold begins to make its appearance. The most pronounced effect is seen towards the end of the 24-hour fast.
Happily, this is probably one of the easiest problems to fix. If you're just sitting at your desk the whole day, the feeling of cold will creep up on you and make you wonder who turned off the heating. But once you've made it past the dreaded hour of brain fog, a great way to crank up the internal heat system is exercise. It's at this point that you begin to feel many of the positive effects of fasting: increased energy, improved mood, feeling of lightness, etc. I find my motivation to do some exercise is also enhanced.
I've tried both aerobic and anaerobic exercise, and the latter seems to me much more enjoyable towards the end of fasting. With running, I get exhausted fairly quickly compared to running after a breakfast, but with strength training I feel a tremendous boost in mental and physical energy compared to just doing nothing while waiting for the fast to end. I'm sure you won't break any records at weight lifting under a fasted condition, but for improving your well-being and avoiding the feeling of cold, strength training is highly recommendable.
5. Trouble falling asleep
This is a common problem with longer fasts and among those who have just started to do shorter fasts. With intermittent fasting, it may take a while to get used to going to bed without a dinner or an evening snack, but after an induction period, it's no problem. You may even find that you sleep better than you did before and need less sleep.
With fasts lasting several days, trouble falling asleep at night may persist. Especially if you're trying to call it a night while you're experiencing one of the more serious hunger pangs, you'll probably find it very difficult to fall asleep. You'll just be tormented by vivid images of cheeseburgers and bacon until you pass out from sheer exhaustion. With dry fasting, you can add cans of soda into the imagery.
While my experience is mostly with intermittent fasting, I've heard that the inability to sleep properly continues throughout the fast despite the fact that many of the other hurdles are already behind. So you'll spend your day feeling energetic and your night feeling, well, energetic. Some ways of relieving this problem are: drinking water to temporarily mask the hunger, avoiding caffeine well before bedtime, and drinking relaxing teas (such as rooibos). And of course, you can simply try to use the time for something more productive than sleeping!
Conclusion
Everybody probably reacts to fasting slightly differently, and the length of the fast will surely affect the degree to which you experience problems along the way. Nonetheless, based on my experiences and those of others, the above list describes most of the common side effects of fasting, along with suggestions on how to deal with them.
Here's a summary of the remedies in neat bullet points:
- Identify the hunger cycle and learn how to 'detach' yourself
- Drink enough water (especially if you're drinking coffee or tea)
- Do something that takes your mind off food
- Wait out the dreaded hour of brain fog
- Hit the gym to improve mood and avoid feeling cold
- Don't drink caffeine before bedtime
- If you can't sleep, do something else!
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