The body is a very complex system and it is so amazing that it works the way that it does! Food to us is like gas to a car, we need it and can't function without it. A simple way to determine calorie need is to use the following formula
1.) Take your weight in pounds (Ex. 150#)
2.) Divide by 2.2 to convert to kilograms (Ex. 150/2.2 = 68kg)
3.) To maintain your current weight multiple by 25 (Ex. 68 x 25 = 1700 calories)
4.) For every 1# of weight loss desired per week week subtract 500 calories per day (Ex.1700 - 500 = 1200 calories to lose 1# per week)
5.) Add any calories back that you used up during exercise, maybe 200 calories for walking on a treadmill.
(Ex. to maintain weight 1700 + 200 = 1900 calories)
(Ex. to lose weight 1200 + 200 = 1400 calories)
In this example 1900 calories per day would be needed to maintain weight and 1400 calories would be needed to lose 1# per week.
For the average person it is not advised to decrease calories below 1200 per day, it will slow your metabolism and make weight loss every harder, DON'T DO IT!
In the example above it is not advisable for someone who is 150# to lose more than 1# per week, losing 2# would make the total amount of calories needed per day 900 which is not healthy. For someone who is 200# it is ok to lose more than 1# per week. (90kg x 25 = 2250 calories per day to maintain weight, 1750 to lose 1# or 1250 to lose 2#)
Remember, slow and steady wins the race! Losing weight the correct way will pay off long term, losing weight in an unhealthy way almost always ends in failure and regaining of lost weight.
Once you know how many calories you need per day you can use these meals to plan your day. They are simply building blocks to reach your total caloric needs.
In the example above a person who is 150#, wanting to lose 1# per week and exercising away 200 calorie per day needs 1400 calories from their diet. This can be three 300-calorie meals and five 100 calorie snacks, or three 300-calorie meals with 100 calorie add-ons plus two 100 calorie snacks. You get the idea... it is all a game of math, kind of like a puzzle, have fun, be creative with your meals and the results will show!