dose it effect if I eat less than the recommended calories?

Eating less than your goal here or there is fine, assuming you are getting proper nutrition overall. Eating 900 calories per day on a regular basis is unhealthy but a couple of days once in a great while is, IMO, not a big deal.

Once in a while isn't going to hurt you but if you can't consistently eat more than 900 calories there is something wrong. You are either not logging everything properly or you are undereating.
Undereating is not good for your health. It can also set you up for a binge which can hurt the weight loss process.

Part of this whole weight loss thing is learning how to balance food.

Once in a while is fine. Three days in a row, not so much. If you are having trouble reaching your goals, I would suggest you try some higher-calorie foods such as nuts, avocado, etc to get your cals up there. 900 cals is very low.

Anoh93 wrote: »

3dogsrunning wrote: »

Once in a while isn't going to hurt you but if you can't consistently eat more than 900 calories there is something wrong. You are either not logging everything properly or you are undereating.
Undereating is not good for your health. It can also set you up for a binge which can hurt the weight loss process.

Part of this whole weight loss thing is learning how to balance food.

The reason is that I spend 12 hr at my university! and I can't find time to eat or it's simply there is no good food to eat all what they got is fast food.
somedays I have the time to make lunch box but others days I cannot...

by the way thank you for your help

You have about 1500 calories to eat before you reach your goal. You should be able to fit some fast food into your diet. Or you can eat more before/after school. Or buy some higher calorie snacks to keep with you. (Nuts, protein bars, candy bars, beef jerky, granola, trail mix, etc) There are lots of ways to get around a crummy schedule.

Anoh93 wrote: »

3dogsrunning wrote: »

Once in a while isn't going to hurt you but if you can't consistently eat more than 900 calories there is something wrong. You are either not logging everything properly or you are undereating.
Undereating is not good for your health. It can also set you up for a binge which can hurt the weight loss process.

Part of this whole weight loss thing is learning how to balance food.

The reason is that I spend 12 hr at my university! and I can't find time to eat or it's simply there is no good food to eat all what they got is fast food.
somedays I have the time to make lunch box but others days I cannot...

by the way thank you for your help

Learn to pack a lunch and/or snacks. Never should mealtime sneak up on you. The majority of people do it multiple times a day, every day of their life, so it's not like it's a new thing. Get a lunch bag and ice packs. Take a yogurt, cheese sticks, boiled eggs, granola bars, veggies, fruits, sandwich, etc. You can eat a yogurt in the few minutes you have between classes. You can walk and eat at the same time from place to place if necessary. Spending 12 hours at your university doesn't mean you shouldn't plan to eat.

VintageFeline wrote: »

I agree with the just eat the fast food comment, You're 1500 below goal, at that level, it's more important to just eat something and generally, fast food isn't that bad, it's just calorie dense so a poor option most of the time when trying to keep within a goal.

This.
I also agree with the other comments to plan ahead too.

Don't be afraid of food. It worse to just not eat. Check out the menu to find some better alternatives that you can eat when I'm a crunch. And start planning ahead.

If you're someone that doesn't have an issue with snack foods in the house, keep something around that's high calorie for days like that. You don't want to go that low under you calorie goal consistently, so if you've gotten your nutrients for the day, having some cookies or something is perfectly fine.

I am just curious that's all. In regards to me I'm going to eat 1500 a day for the next two weeks. I'm allowed 2000 calories a day, il be under by 500 a day. That should be 2lbs of fat I hope