A question about fiber and diet balance

There is always the 80/20 rule. Saying that if you are on plan 80% of the time, you are doing good. The other side to that is just how far over you go on your off days. If your goal is 1680 and you rarely go over 2000, chances are you are still within your maintenance range assuming you are going for a 1 lb a week loss rate. So though it will take a tad longer to hit your goal, if it's maintainable and works for you. Go with it.

I don't know how you do shakes for more than one meal. I'd be gnawing my arm off. To each their own. Stay with calories 5 days and within maintenance on the weekends and you will lose.

Addressing your title and first-paragraph question head on:

Nutrition is IMO a matter of getting the right nutrients, overall, on average, ideally over small time periods (i.e., over a day or few).

Your dinners have nutrition (protein, fats, you mention veggies which will have fiber and micronutrients, etc.). If those, plus your lunch/breakfast (which also bring nutrients) add up to the necessary minimums of proteins, healthy fats, fiber, micronutrients (broadly interpreted), then you're golden. If you're a little over on one thing one day, a little under the next, averaging out to roughly the right level, you're still golden. Humans are adaptive omnivores.

In the context of weight loss, it's primarily an matter of individual sustainability when during the day you eat particular nutrients, with a couple of quibble-y exceptions**. If your eating schedule makes it easy for you to stick with your calorie goal, that supports weight loss. If it doesn't do that, a change would be a good experiment.

There's some research, most of it not ideal quality, suggesting that eating timing may have some minor impact on people's weight loss rate, and there's other research reaching the opposite conclusion. Even in the studies I've seen finding a benefit from one timing scheme vs. another, the difference is so small that I'm personally convinced it pales in comparison to the impact on whether a person can stick to their calorie goal happily for long enough to achieve their weight-management goals.

** Example of quibble-y exception: There's some research consensus now that aging people, say age 50-60 and up, benefit from spreading protein through the day, rather than concentrating it mostly in one meal, because we metabolize protein less effectively as we age. During weight loss, and in general, spreading out protein can help li'l ol' ladies like me keep muscle mass while we lose fat.

Here's where I get really opinionated and subjective: I'm curious, now, about what your dinners consist of, that you consider "lesser healthy" or "junk".

Personally, I have some skepticism about meal replacement shakes. I'm old (66). Over my lifespan, science has "discovered" many essential and beneficial nutrients - vitamins, minerals, other useful phytonutrients. Once those are discovered, they tend to be formulated into supplements and meal replacement shakes, usually with much marketing fanfare. The thing is, they were in regular foods - foods humans have eaten for centuries and millennia - all along.

I'm doubtful that we've reached a magical point now, where science actually tells us everything we need to know about nutrition. Therefore, personally, I consider it a good bet-hedge to get most of my nutrition from regular traditional foods, and a well-rounded range of those.

I'm not saying there's anything wrong with using meal replacement shakes, if they help you personally reach (known) nutritional goals, and achieve a healthy body weight. Those things are more important, I think, than undiscovered nutrients, in an individual case.

Why I'm saying all this is that we see some people defining foods as "unhealthy" or "junk" using criteria other than nutritional content and calorie density. There are people criticizing "highly processed foods" but relying on protein powder for a big chunk of their protein intake, when many protein powders are objectively "highly processed foods" by any sensible definition. We see people thinking that plain potatoes are unhealthy, because they're white, or "a carb", when a potato (like a baked potato) is quite nutrient-dense for its calories, and survey research has found it to be one of the most commonly filling foods. And so forth.

Categorizing foods as "healthy" vs. "junk", "clean" or "whole" vs. "highly processed", "good" or "bad" for nutrition and health . . . that can distract from what I think ought to be the main goal, getting good overall nutrition and appropriate calories from foods an individual finds filling, practical, and tasty (so that they can stick with their routine long term). That latter, nutrition at appropriate calories, is the key thing for nutrition, weight management, health.

Sorry, long-winded rant! Bottom line: If changing what you eat and when you eat it helps you get nutrition, so stick with your calorie goal happily, that's a good thing. That kind of personalization, IMO, is a key success factor, and details will differ individually.