How come when i eat sandwich and fruit & veggie stix for lunch i get hungry by 3 but not when i eat fast food?

Because you aren't eating as many calories. The fiber in fruit is filling, but it only works for so long. I recommend that you load your tummy with protein at lunch, that should keep you going. But really, the answer to your question is that when you eat fast food, you are getting a meal of 1000+ calories. Your healthy lunch is only about 300. Maybe add some yogurt/cheese and some form of complex carbs to it. A bigger meal with lots of fiber and protein should do the trick. Also, fast food is loaded with fat, which sticks in your stomach for a while. To achieve this effect without the burger, throw in a handful of nuts. They are so healthy and full of unsaturated fats, thee good kind. And the fast food is sooo bad for you. Although it keeps you full, that's only because it's packed with empty calories. You're really not getting any energy from it, which is what good food SHOULD provide you with. Nice job on picking the healthier lunch, though.

The amount of fat in the fast food is higher than in the sandwich and veggies. That's why you're fuller with it...

The fast food may keep you full longer, it really isn't better! Eating healthy smaller meals more often will keep you full and speed up your metabolism. OR try adding more protein to your sandwich!

The fat content in fast food remains in your system longer making you feel fuller then your sandwich and veggies. If you're still hungry, eat more veggie sticks! Or try eating a salad for lunch with a meat product (chicken strips/ham ect) and a low-fat dresing.

Well, you didn't say what was in the sandwich or the fast food but I can tell you that research has shown that high protein meals will keep you from feeling hungry longer than high fat or high carbohydrate meals. Even when all three have the exact same number of calories.

I frequently eat left-overs for lunch which could be something from spaghetti to mashed potatoes to soup to grilled hen sandwich to chili. I many times have carrot and celery sticks with lunch too. at the same time as there are not any left-overs I many times make a peanut butter and grape jelly sandwich or a Swiss cheese sandwich with mustard.

That happens to me too. Fast food has more meat and fat in it and grease which takes longer to digest. You can eat fast food a couple days a week, but try to eat healthy the rest of the week.

Fast food has much more calories, but is unhealthy. If you used whole grain bread (fiber), more peanut butter/turkey/chicken(whatever you put on you sandwich) (protein) and drink water with the sandwich it will fill you up faster and keep you full longer.