Question on impact of Caloric Intake

When you eat food, the weight of the food is transferred to your body immediately. The nutrients and calories are processed over the next few days. So you see different effects from the food over different periods of time, but no -- the calorie impact doesn't show up immediately.

It takes a certain amount of time, which can vary. I don't have a cite on hand, but saw a research study that suggested full digestive transit can take up to 50+ hours. Presumably large amounts of nutrients/calories are absorbed early in the process, but some potentially along most of the route.

I'm wondering why this is useful (or is it just curiosity)?

I've been tracking my weight daily for years, even before I seriously started trying to lose some (and now I've been maintaining a healthy weight for 5+ years, still tracking food & bodyweight). I think it can be informative to weigh daily (under as consistent conditions as feasible), and that it can help a person understand what their own individual body does under different circumstances. (People who are very stressed by scale fluctuations should probably *not* do this. To me, as a data geek by nature and professional background, it's just a fun science-fair thing, not emotional at all).

When I materially over-eat (substantially over maintenance calories), it's normal for the scale to go up for reasons having nothing to do with fat gain, and to start that immediately. (At first, purely the extra weight of food/liquid in digestive transit; later, what enters the picture is more about water retention that's a normal part of metabolizing carbs and balancing electrolytes from the additional food.) Usually, the scale will be up for a couple of days, for these essentially meaningless reasons. (Meaningless because not about fat gain/loss.)

So, I won't see any fat-based fluctuation on the scale for a few days (it's obscured by the meaningless stuff). By then, I will have had other days, maybe below/at/calorie goal, and they have their own effects. If you made me guess, I would guess that in a practical sense it takes fat gain at least a couple of days to show up.

However, a person needs to eat around 3500 calories above their maintenance calories to gain a single pound of fat. That means, for me, I'd have to eat something in the 5000-6000 calorie range to gain a pound of fat from one day's overeating. I can do that (even as a quite-small li'l ol' lady), and on the rare occasion do. Thing is, if I do such a thing, various after-effects happen.

For one, I think I will have overwhelmed my body's usual mechanisms for harvesting calories & nutrients at the levels I've trained it to expect. My suspicion is that when this is a *rare* event, it will absorb a *slightly* reduced fraction of the calories/nutrients in that food, and pass it through to waste. By observation, I (and others on whom actual lab tests have been done) will see my resting heart rate up the next day, be more likely to have hot flashes or generally feel warm, may have extra-energetic workouts or get more stuff done around home. Bodies aren't static. Sometimes, given them more input causes more output.

tl;dr: It's complicated, and really doesn't matter much, if you ask me. What matters is the cumulative effects of habits, over much longer time periods.

You might find this fun:

https://www.youtube.com/watch?v=j6cIbIvEGJM

You can easily find her video of the day where she did the over-eating, too, on YouTube.

Observe your general weight level change over (sufficient) time by using a weight trend app that "smooths" out temporary fluctuations