A Reddit discussion theme brought this up, related to me practicing and following discussion about fasting. I've experienced limited changes in food preferences that seem to relate to fasting, but then I've only ever fasted three times for 5 full days, and two other times when I stopped earlier, after 2 or 3 days, mostly related to getting electrolyte input wrong, I think. I've wrote about that here.
That starting point input is this, from that post and discussion:
I have been fasting for a couple of weeks and apart from losing a bit of weight, realized I obsess less about food now. Anyone else experience this. If so, what are the reason for it?
I don't think I ever did obsess about food so much, but it will work as in intro to describe what I think changed. I had snacking habits before that seemed to mostly drop out. I would eat just a little chocolate regularly, and for awhile (even after the two rounds of fasting) I had switched to snacking on mixed nuts between meals. It wasn't really a negative thing, as I saw it, or an obsession, but I feel even more inclined to just eat three light meals a day now, which really isn't far from how I saw my diet a year ago, before the fasting trials.
Someone mentioned a good reference on food craving experience, the psychology of that, which is a summary of lots of other reference materials. From scanning their definition of food cravings maybe I never did experience what they describe as that. I was more into ice cream before, which I would sometimes eat when it was around, but I never saw that as a craving experience.
Rather than go through a summary of the research paper contents, building up from background and definitions, it could be more interesting to start with what they say about fasting changing food experience or habits:
One area in which food cravings appear responsive to dietary reductions is fasting. The direction of change is unexpected. There is evidence that fasting, in both the short-term (Lappalainen et al. 1990) and the long-term (Harvey et al. 1993), is associated with fewer food-craving experiences. This decrease in craving is generalised across all food groups and does not rebound during re-feeding (Harvey et al. 1993; Martin et al. 2006). While such interventions are effective at bringing about weight loss, there is no relationship between the amount of weight lost and reduction in food craving.
This suppression of food craving is consistent with other observations of reduced appetite during weight loss on very-low-energy diets. The paradox ‘less food, less hunger’ is the headline of a study by Wadden et al. (1987)...
Interesting, right? I'll consider some perspectives from comments in that Reddit discussion and then come back to tying it together with these ideas based on my own experience.
Reddit discussion inputs, versus my experiences
Let's just start with the first two comments, I guess sorted by Reddit karma (upvotes, their version of FB likes):
I usually go through a phase in my fasts where I obsessively scroll r/FoodPorn... so, I guess everyone is different. I do feel more control over my eating though. I use to need to eat every 3 hours or I might punch a baby for looking at me the wrong way. Now 16h is hardly noticeable.
It is interesting how people react to hunger or cravings in different ways, or take the whole experience very differently. There seems to be a divide between people who avoid any contact with food or the idea of food and others who actually keep in touch with the subject while fasting, as that person does. Some contact with food exposure while fasting is fine but it seems as well to avoid that, and scrolling the internet related to food content.
There's probably several reasons why this happens (biological, psychological, changes in environment, etc) but I think biologically it's because fasting has a powerful moderating impact on hormones related to hunger.
Hunger experience, and how it changes with fasting exposure, is one of the most interesting parts of exploring fasting. Not just for abstract self-understanding either; it plays into enabling a different form of control over a main bodily input like eating. Not just related to not eating, also tying to managing inputs, to eating healthier, to placing snacking in relation to meal inputs differently, and better.
These two inputs tie together quite well with a very general exposure theme I experienced, that links to the point about fasting causing less hunger experience in the end.
The first 2 or 3 times I tried fasting the experience of hunger was very intense. It just seemed normal to me that people would always experience that. I might also mention that I decided to fast once when I was 10 or 11 or so (I was a strange kid; I had no exposure to the practice of fasting at all at that point), and only made it through one nearly complete day. Related to how people fasting count the time that probably was 26 hours or so, maybe 28, so one full day. I didn't know what to make of the experience then, beyond that hunger experience would be intense. I wanted to go a full day then, so more like 36 hours, but hunger was driving me crazy, and I ate some cake my family had eaten earlier.
Fast forward 40 years and I tried it again (with some juice fasting in the middle; that's easy enough to do for a number of days, because in a sense you are still "eating," ingesting calories). Experience of hunger was intense. The worst of it lasted 3 days or so, easing up after that. It came in a few different forms, as a base-level feeling of emptiness, as gnawing desire to eat, and as cravings, as immediate urges to eat something I normally would at that time, or triggered by seeing or smelling a food. The very first day--I don't remember if for an attempt that didn't work or the first 5 day duration; I think the latter--I visited a food market with my wife, and it wasn't so bad, beyond the smell. Visiting a local fair and restaurant with her the next day also was fine; somehow working through the expectation of eating was no problem.
I was a four days into fasting at this street festival last year
I ended that fast late into my birthday so I had cake and ice cream
Then on the last 5 day fast hunger had dropped out relatively entirely, at least related to those earlier experiences. My body seemed to adjust, perhaps related to the hormone experience mentioned in the second comment. I think expectation at the mental level was also a factor; it was easy to just not attach to the idea of eating, to not try to not think about it, since that cycle of avoiding thoughts or desire can be problematic, to instead just accept it and let it go.
Back to the "craving" idea I'm not sure to what extent I ever fit the criteria in that paper, which explicitly describes that there is no singular clear definition of that. It's a research review style of paper, so it talks around how different studies interpret cravings a little, but then mostly just sets that aside. I picked up the habit of mostly eating three small meals a day so many years ago that it's hard to keep track; I don't snack that much. In college we had cafeteria meal plans set up that way (freshman and sophomore years in the dorms), and my parents always tended to eat like that, with an evening desert as an exception.
It's hard to summarize how it works out related to "less food intake equals less hunger," but thinking back I have some history with that. I was really thin for my entire 20s and through most of my 30s, in part because I was vegetarian, and because I led a very active lifestyle, for work and sports, and fueled that by eating three moderate meals a day. Through habit I mostly only ate when hungry, channeled down to those meal times, with some evening snacking included. Maybe as much related to the vegetarian diet theme I think I kept caloric intake to an absolute minimum, to the extent that whenever I wasn't working or exercising if I would just sit down my body would crash. Reading was a favorite hobby interest then, which matched well with that.
I tried to practice what I later heard referred to as "intuitive eating," which I didn't have a name for. I tried to eat what I felt hungry for, adjusting for tuning into what my body needed, versus letting ice cream, potato chips, and McDonald's food become that default. I didn't drink soda or eat candy much, even though I think I was cutting it close on caloric input, so it would've been natural to crave that. Maybe a work-around was eating foods like trail mix as a snack, eating just enough to fuel the exercise and other processes. I kept busy so I never noticed being hungry, until the next meal time brought it up, and by then I needed more food intake, so it all seemed quite natural. I was 5' 8" and weighed 150 pounds or so, as skinny as could be, but my body was fine with the cycle.
camping in Canyonlands in Utah in the 90s; I would've hiked 10-15 miles a day back then
what that looked like, but this was across the border in Colorado
I'm an inch shorter now (people do tend to shrink as they age), and weigh 15 more pounds, but I seem to eat less than ever. We seem to get into equilibrium states, and then change to become heavier or lighter isn't as natural as continuing on, if it all balances.
Fasting as a diet reset
One other part links, that is so distinct that a new section seems in order. Even though I've just described eating a fairly healthy diet in my 20s (and I'm in my 50s now, and that never completely changed) fasting has seemed to help serve as a positive diet reset. More than ever I appreciate and desire eating healthy, nutrient dense foods, like fruits and vegetables, complex salads, and healthy versions of soups and stews, or plain grilled meats and vegetable. I've been eating a lot of pumpkin and sweet potatoes for years; that didn't change.
It's not really directly related but I've been supplementing protein intake for about a year, drinking powder mixed into milk or juice, because I try to not eat too much meat, eggs, or dairy, but my protein demands seem considerable related to running a good bit (15 to 20 miles a week). Why wouldn't I crave meat, dairy, and eggs, if I'm implying here that natural intuition can guide more ideal diet inputs? I don't know. Maybe it all doesn't actually work, and I'm only experiencing what I expect to experience. I don't crave the protein shakes, at all; I have to remind myself to include that, and often skip it when I planned to but forgot (like with breakfast recently, and yesterday's).
Where I go (physically) seems to partly guide diet as much as these mental factors I'm bringing up. In visiting malls or shopping complexes I walk by Dairy Queen (which is still more popular here than back in the US), and in the past I'd eat more of that.
some product offerings are a little out there but I like others
I'm separated from my kids now, and my normal routines, because they're in Honolulu in school and I'm working in Bangkok, so I've not been in malls much for six weeks, and haven't eaten any ice cream in that time. Thai foods tend to be fairly healthy but I'm almost entirely off those now too, cooking simple and basic food versions at home more. I go to work in an office infrequently, about once a week, and what I eat there is mixed; sometimes food I bring, sometimes just a pastry or snack out doing an errand, or a couple of times fast food (back to McDonald's, once in that month or so). It's not like I'm on an ideal diet; I saw Oreos on sale at the grocery store and picked some up, and since I was craving chocolate (maybe from mentioning it here) I bought chocolate covered digestives too.
So what really changed for me, related to this "reset" idea? I had mentioned that when fasting I noticed a few layers of triggers of what or when to eat, and a snacking response was part of that. My main version had shifted from chocolate to mixed nuts, eating a small handful a few times a day, but that was probably based on immediate triggered impulse as much or more than a real dietary need, caused by an intake gap. It's not problematic, eating a half a cup of mixed nuts a day, so it doesn't really work as an example of "corrective action," but the theme isn't different than if it had been chocolate, ice cream, chips, or whatever else. I've eaten a lot of salads at different times, but cycling back to that as a habit is another example.
Living in Honolulu with my wife in grad school (where we met) if I ever asked her what she wanted me to make for dinner she would always say salad, every time. Then I would make an elaborate version of that, with greens, lots of vegetables, extra inputs like raisins or sunflower seeds, home-made dressings, something like soy and sesame, a fruit input, homemade croutons from seasoning and toasting bread, and often with chili seasoned fried tofu. She loved it because it's not a typical Thai food, and no Thai would ever experience such an elaborate version. Even if they wanted to vegetables are different here (I'm in Bangkok now), and the set in the US somehow seems really well suited for that.
People in that Reddit fasting sub are more concerned with dieting than I am, naturally. They will use rotating fasts (rolling 48s or 72s, two or three day cycles on and off eating), or 2 or 3 week long fast durations to maximize that. I could also stand to lose a few pounds, I guess. Some people in that group talk about shifting habits even more than I've described, cutting out more negative inputs. Here's a typical example, from the thread I mentioned as a main starting point:
It’s because the ultra processed / sugary stuff that most people eat is addictive. If you cut it out you won’t crave it anymore after awhile.
That probably works. Two separate comments second what I've said about the fasting experience time-frame shifting with exposure:
The first few times I fasted I obsessed really bad, that was the most difficult part. Over time it has mostly gone away.
So it wasn't only a research review paper, it summarized a series of papers and ideas presented together, back in 2006 ("The Summer Meeting of the Nutrition Society, hosted by the Rowett Research Institute and the University of Aberdeen"). An excerpt of the abstract points to more overlap with what I'm considering here:
Cravings are hedonic responses to food, characterised by their intensity and their specificity. Food cravings are extremely common, reported by the majority of young adults. They are closely associated with liking but not synonymous with increased intake... Taking dieting as an example of an assumed influence on food craving, the outcomes of cross sectional studies are mixed and unconvincing. Prospective and experimental research shows a clearer relationship. Dieting or restrained eating generally increase the likelihood of food craving while fasting makes craving, like hunger, diminish. Attempted restriction or deprivation of a particular food is associated with an increase in craving for the unavailable food...
It's all worth a read, just a little dry.
To add one more experiential observation before closing I've noticed since fasting that I tolerate short term hunger experience better, seemingly less triggered by expectations. I can skip a lunch and I get hungry, as anyone would, but if I eat a good sized late breakfast that doesn't apply, so it's not just about expectations. Expecting a meal input and actual hunger, bodily demand for calories, seem to be two different things.
One supposed benefit of fasting is "metabolic flexibility," the ability to use body fat as an energy input, and to some extent it seems to work out like that. I can go quite light on eating for a day and still run 10k (6 miles) and don't really notice much difference. Doing light runs during fasts may have helped with acclimation for that. Before the fasting exposure it seemed like draining glycogen reserves during such runs triggered even more immediate hunger response, and now as long as I eat something later it doesn't really matter if it's calorie dense of not; a large salad will do.
My phone health app says that I "only" burn 600 or so calories on a 10k run (actually 529 for a 10.1 k run yesterday), and supposedly we store 2000 calories of glycogen reserves in our body, which is why running a 42 km marathon has people hitting a wall when that supply runs out. Runners can avoid that by eating energy gels and such, or drinking Gatorade, or even by acclimating to use body fat as energy better, back to the metabolic flexibility idea. I suspect that there is a huge difference in running efficiency at different paces, that my phone app really isn't "in on," and someone running a 3 hour marathon versus a leisurely 4 1/2 hours adds extra caloric demands. But what do I know; that's just a guess.
For me fasting is about experiencing the experimentation, along with limited interest in health benefits that I could never really confirm anyway. My own shift in eating patterns and the experience of hunger seems moderate, but it's still interesting.
In the long run I think it can be valuable to switch around how we see food, to change from considering only what would be pleasant to experience as a next flavor input or satiation experience and instead also consider nutrient intake, what balance of foods may support that. Of course that process can start at the grocery store, for people stuck in the past who actually prepare foods, or it would extend to what is purchased through an app for many others. Over time it's easy to appreciate healthier food inputs, or I suppose even to crave them, depending on how you define that.