Low calorie diet

I really need some advice, I’m new to all this.

So when I’m trying to lose weight, if I don’t see results quickly I unfortunately get discouraged and give up. I decided to start a low calorie diet, hoping that if I can lose like 5 pounds pretty quickly that will give me some motivation to keep going. I’m doing a 1,000 calorie diet, and I walk about 4-5 miles daily. Most days I usually eat less than 1,000 and more around 700 calories. I’m just worried that I may put my body in starvation mode tho. Has anyone ever lost weight and kept it off with a low calorie diet???

I want to lose 40 pounds