Humm - well, assuming you have no particular health issues that would make it a bad idea, and assume that your one ‘meal’ is well balanced, has enough protein, fiber, vitamins and isn’t crazy heavy in fat, sugar or sodium, you’ll probably be fine. I’m basing this on the fact that loads of people eat just this way and are perfectly healthy for years and years. When I met my husband he only ate one meal a day - now, he actually wanted to GAIN weight ('cus he was kinda on the thin side) so I’ve been feeing him more often and he’s up about where he wants to be.
However, just as another data point, when people join Weight Watchers one of their primary tools is to get people to eat more often - not whole meals, but snacks - like a handful of carrots, or an apple, or whatever. This DOES help regulate blood sugar and if you were going to follow GI diet rules it seems like a good idea.
Ultimately, you just need to find something that works for you and is sustainable in the long term. Personally, if I only ate one meal I day I would probably stab someone before noon, but everyone is different.
My understanding is that an average person would likely gain weight on that system. You already understand that in the short term a body responds to intermittent fasting in ways that often end up putting more weight on; what reason is there to believe that doing this in a prolonged manner would change how the body responds?
Most people would end up being ravenous at that meal and eating more than they otherwise would if they spread out their calories over the day.
There is no reason to think that what you propose would decrease your overall calorie intake, increase the nutritional density of what you ate, increase your energy expenditure out, or make your body less efficient at putting what you eat into fat. There is, conversely, some good reason to believe the exact opposite would be true in each case.
IMO, eating one meal a day if you’re trying to lose weight is about the single worst thing you could try. You’re almost guaranteeing that you won’t exercise (which is part of being healthy, regardless of your weight), you’ll have swings of hunger and binge eating, and you will spend a good chunk of your day thinking about food. If you don’t have the discipline to eat healthy with three meals a day, there’s no reason to think you’ll eat healthy with one meal a day.
I get quite a bit of on-the-job exercise and I walk a lot, as well. I drink lots of water and decaf tea or soda throughout the day. I don’t suffer from wanting to binge or have many hunger “pangs.” My cholesterol and bp are quite low and I weigh 107 and am 5’2". Not my only motivator, but I just think it’s fun to enjoy my evening meal without really having to worry about counting calories. I don’t overeat or binge at this meal, as I can’t stand feeling overly full, but I may have that piece of bread or an extra glass of wine. No biggie.
I eat one big meal a day with a few small snacks. One could call them meals. I try to have something right when I wake up, and it’s usually not what most people would eat for breakfast. However, I only eat because I know I need to - I’m struggling with severe depression and very rarely feel hungry.
I’m a bit wary of the one meal a day thing, just because of the possibility that my bod would decide to go on starvation rules.
I get as near that as feasible for me. I have one (100-cal) granola bar for breakfast with my vitamins and tea, a full dinner-sized meal for lunch - vegetarian about 3 times a week, and a bowl of clear soup or a couple pieces of toast for a late dinner. The soup or toast keeps me from getting hungry in my sleep.
I drink tea constantly all day, caffeinated during the day and decaf in the evenings.