(That comment was in response to Craig, but a glitch apparently decided to delete the quote giving it that context.)
Regardless, as the little infographic that I posted covers quite concisely, weight loss is achieved first and foremost from a net caloric deficit. This means consuming less calories than your body uses in a day.
As far as weight loss is concerned, it doesn’t matter what you eat as long as you’re in a net caloric deficit. You could eat nothing but ice cream, twinkies, and candy bars and still lose weight. On the flip side, if you are in a caloric surplus you will gain weight regardless of what you eat (Even salads, Soylent, and detox smoothies). So why bother eating healthy? Because you’re giving your body what it needs to function like it should. You’re also more likely to feel full, energetic, and less achey/groggy.
To elaborate more specifically though, you can’t expect a single food item to change the whole of your body’s nutrient intake. If you’ll pardon a musical reference, it’s the overall chorus of everything you consume that makes a difference, not an individual note here or there. That’s why fat loss pills don’t work, that’s why “this one simple trick” doesn’t work, etc.
Going back to your original question, “Can Soylent help a 375 lb man lose weight?”, of course it can. But not as the cause of weight loss. Soylent is just food, a convenient and healthy food, but food nonetheless. A net caloric deficit will always be the cause of weight loss. Now you certainly don’t have to count calories if you don’t want to, but you’ll need to be in a deficit regardless. I’m just guessing your statistics here, but at worst it looks like your body might be consuming 2000 calories a day. It’s entirely possible that your body might need 2800 or more calories just to sustain your current weight given more activity (or other variables that I might have guessed incorrectly).
I’d really recommend checking out that infographic though. It explains a lot in a concise and straightforward way. If there is something about it that you don’t get, I’ll be around if you have any questions, or feel free to scour the internet. Good luck!