There are 3 things you need to keep a diary of: food, exercise and body shape. Read below on how to use them:

Food Diary

A food diary records all the food and drink you consume day-in, day-out. Also, a food diary allows you to take an objective look at your real eating patterns. Many people who feel that they “hardly eat anything” will be amazed at their forgotten or unintentional eating activities.

How to Fill It Out
Record what you ate and drank for breakfast, lunch, dinner and anything in between for everyday of the week. Also be sure to record the times you ate.

How to Utilise It as a Tool
If for example you lost 0.5kg of weight in a week, you could look back over your food dairy and see what foods you consumed and what eating patterns you followed that helped you get such a fantastic result. Then you could replicate the same eating habits (and activity levels) for the following week and see if you get another weight-loss. Alternatively, if at the end of a week you didn’t loose any weight, you could look back over the diary and see where you can reduce food (calorie) intake (or increase activity levels).
NOTE: This tool is best used in conjunction with the other diaries.

Exercise Diary

An exercise diary records all the physical activities you have done day-in, day-out. This includes shopping, taking the dog for a walk, playing sport, going to the beach, house chores, hitting the gym, etc.

How to Fill It Out
For everyday of the week, record what activity you did, how long you did it for and what time you did it. Then record the total amount of time for the activities undertaken that day. Then, at the end of each week, record the grand total amount of time for the activities undertaken that entire week.

How to Utilise It as a Tool
If for example you lost 0.5kg of weight in a week, you could look back over your exercise dairy and see what types of activities you performed and how much time you spent exercising during the week, which resulted in such a fantastic weight-loss. Then you could perform similar exercise patterns (and eating habits) for the following week and see if you get another weight-loss. Alternatively, if at the end of a week you didn’t loose any weight, you could look back over the diary and see where you can increase exercise and activity levels (or reduce food intake).
NOTE: This tool is best used in conjunction with the other diaries.

Body Shape Diary

A body shape diary records information about your body shape, so you can compare data taken at a later date and gauge progress.

How to Fill It Out
At the beginning of your weight-loss journey, write down the date and record various information using any of the following methods.

• Weight reading from scales (be sure to write down the time you weighed yourself and the last time you ate, so you can closely replicate later on)

• Girth measurements (measuring certain body parts. e.g. waist, thighs, arms)

• How your clothes feel 

• Pants, shirt, belt or dress sizes

• A current photo of youself

• Fitness tests (e.g. how long it takes you to walk 500m, how long it takes you to cycle 2km)
  

How to Utilise It as a Tool
At the end of each week, fortnight or month, retake the body shape data and compare it to the original/previous record. If there was a positive result, then use your exercise and food diaries to replicate similar exercise patterns and eating habits for the next period and see if you get another positive result. Alternatively, if you retook the data and did not get a positive result, you could look back over the exercise and food diaries to see where you can make changes in food intake/timing and/or activity levels to get a positive result next time.

NOTE: You can still get results without using a diary system. The above is just one method that can be implemented.