Will eating late at night make me gain weight?

You can argue whether you will have a higher or lower heart rate overnight and whether digestion will hinder your ability to sleep as well and for your body to repair itself.

Whether any of that will affect your weight other than via the presence or absence of processing by products in your system is up for grabs.

Your week long experiment doesn't account for that flaw, therefore it will not give you the real answer you're looking for (assuming that you are looking for one)

So here's the thing. Optimization is awesome! Eat a large breakfast, medium lunch, little dinner, sleep like a baby, exercise like a fiend, eat perfect macros, awesome combination of pristinely produced foods that meet all ethical considerations home cooked lovingly and never over eaten with awesome timing of protein and carbs around your exercise. Oh, and don't forget quantities of fruits and veggies and fish and calcium and vitamins and antioxidants and....

And then there is the real life.

Some optimization may matter a lot to you as an individual especially given your individual medical status . But some of them may not matter as much to Pete or Sue.

So every Pete and Sue had better find what gives them the biggest bang for their buck. Because trying to get everything optimized is likely to lead to nothing happening. Or of overdoing things so much that you end up on with the opposite type of disaster.

Timing of food is one of these things.

Can we come up with support for optimal timing? There's studies that do show advantages. Though I can't say that I've seen too much on exactly how much of an advantage.

So does this mean that nobody on night shift can lose weight?

Or that I couldn't lose a good 125lbs and maintain that loss for more or less the past 10 years while eating food at 8pm, and 1am and 3am including at times most of my calories for the day? I think that you can guess the answer.

And yes, 10 years later I'm actually trying to eat earlier at night because I can see the effects of late meals on my overnight sleeping heart rate. But that is NOT a weight control related optimization.

To lose weight you need a deficit. Period. Full stop. Nothing more and nothing less. And you need to be able to apply it over time.

So doing some optimizations and making some changes IS necessary, I won't hide it. We know how many people regain their losses. But every optimization and complication we introduce has to be evaluated (by us) as to whether it is worth it to us. Will this give me bang for the buck? Does it make my life easier and adds to my ability to create a deficit?

Physiologically I don't see a mechanism (or a believable functional doctor explanation) that explains how a vastly different amount of calories can get burned by eating early vs late. I can see some marginal issues about hunger, about energy availability to muscles, about elevated or lowered metabolic activity through the day (fasting did come partially from people looking to lower metabolic activity to increase life span).

But these margins are maybe discussing 50Cal and not 500Cal. While uncontrolled hunger and binging can easily add up to 1000 or 2000 or 5000Cal.

Make some difference? Maybe. Prevent weight loss? No.

Any studies I've seen show at most minor effects from eating timing.

Here's the thing: Having a routine that's personally achievable matters more. It doesn't matter how good something is claimed to be in theory - not eating close to bed time, drinking green tea instead of Coke Zero, HIIT workouts instead of casual walking, whatever pop-sci stuff is showing up in the blogosphere and tabloids as weight loss magic.

If I can't stick with it, it's not going to work in practice, no matter how ideal it is in theory. Something less theoretically ideal that I can stick with can work, as long as it helps me eat manageably fewer calories than I burn.

I have to admit, not eating all day then getting home so hungry and in pain that I'd want to eat the kitchen and all of its contents . . . that wouldn't work for me, because I'd overeat. Maybe that's not true for you. Certainly, some people report their best success with OMAD, one meal a day time-restricted eating, and some of them eat that at dinner, late in the day. OMAD would make me fail, because it would make me miserable. It makes them successful. These individual differences matter.

Do what works for you.

Me, I eat on a variable schedule, when I feel like it, potentially any time from shortly after I get up the morning to shortly before bed, occasionally even in bed. Sometimes I eat late, sometimes I don't. I've seen no effect of those timing differences on my weight loss trend. That's been true for just under a year of weight loss, and 9+ years of successful weight maintenance since.

Sure, if I eat a big fiber-rich and high fluids dinner right before bed, my routine morning weigh-in the next day will show a higher body weight than if I'd stopped eating several hours earlier, and visited the bathroom a few times before bedtime. That's not about body fat. That's because a serving of plain water or an apple weigh just as much in my digestive tract as they weighed sitting on the kitchen counter, until my body fully digests/metabolizes them and jettisons the undigestible residue. Fat gain or loss shows up in a multi-week trend of body weight, not in the random fluctuations from one day to the next.

My reading and my experience suggest that when it comes to weight loss, worrying about eating timing is majoring in the minors. The main focus is finding a personally tolerable new routine of nearly any description that results in eating manageably fewer calories than the person burns, and repeating that fairly consistently over quite a long period of time.

Best wishes!