Thing is, vegetables have varying amounts of carbs that can set back your low-carb diet. For example, celery, broccoli and lettuce are very fibrous and humans

Thing is, vegetables have varying amounts of carbs that can set back your low-carb diet. For example, celery, broccoli and lettuce are very fibrous and humans don't really digest the carbs, so they have little impact. Probably only ruminants can extract significant nutrition. On the other hand, in roughly increasing order of carb content, tomato (technically a fruit), onion, carrots, potatoes, corn, wheat products, and rice will reduce the effectiveness of a low carb diet, especially if dieters are told it's ok to eat vegetables all day long without specific guidance on what to avoid. I agree that ultimately it comes down to the rate at which we put energy into our bodies vs the rate at which our bodies use the energy and don't store it as fat. Unfortunately, there are confounding factors that make this a simplistic heuristic. Things like underactive thyroids, insulin response to blood glucose fluctuations, our basal metabolic rate, and similar things, many of which are often genetically determined. I believe that a really important reason to do a low-carb diet with moderate protein and enough fat for satiation is that it is much easier to sustain as a permanent lifestyle change than a low-fat diet, which in my experience leaves one often feeling hungry and unsatisfied. And the permanent change is what is needed for long-term success.