Is vegetarianism a good way to lose weight?
The key is to make your meals from scratch, and if you do, a high fiber, nutrient rich vegetarian diet will work almost like magic for weight loss.
But if you consume too much sugar and ultra-processed vegetarian food — and there's more and more of it these days — you will surely gain weight. Some processed foods like refined seed oils (soybean, canola, safflower, etc.) are obesogenic regardless of calories. Stick with virgin olive oil, avocado, and coconut.
With a vegetarian diet, as with any other diet, food quality is what matters most.