Most of the information that I present here is public knowledge, based on scientific understanding, proven by scientific methods and decades of experience by dieticians, drug-free bodybuilders, and other people who have successfully reduced their body fat. As you will read, the most successful method to lose body fat in a sustainable manner is through a combination of reducing daily calorie intake (how much you eat and drink), eating correctly (what you eat and drink), hunger control (what and how you eat and drink), and physical activity (exercise). 
It is not my intention to tell here a very extensive story that explains every aspect in a detailed and highly scientific manner. I rather prefer to keep this a concise and practical guide that can be used by anybody, irrespective of age and background. If you want to know more on any specific topic, I advise you to consult wikipedia.org or search the internet. 

Reducing your Daily Calorie Intake 
Body fat is stored energy that the body will only use during periods in which there is not enough energy directly available from your food intake. The amount of energy is expressed in terms of calories. One kilogram (2.2 lbs) of body fat contains 7,000 calories. The only way to reduce your body fat is by lowering your daily food intake so that the body starts burning the stored energy supplies (body fat) to get the energy it needs. 
The body needs energy (calories) to perform its basic functions to stay alive (body temperature, thinking, breathing, digesting food, etc.) and to perform physical work (walking, working, exercise, etc.). The total number of calories that your body uses daily depends on your gender, age, length, weight, muscle mass, and physical activity. The simplest (but not so accurate) method to estimate your daily caloric need is to multiply your body weight in kg by 33 (or multiply your body weight in lbs by 15). The most accurate way to determine your personal daily caloric need is to count your average daily caloric intake during a long period of stable body weight. 

The only way to reduce your current body fat is by letting your body burn more calories than you eat and drink. This can basically be accomplished in two ways: by keeping your daily caloric intake below your daily caloric need, or by increasing your physical activity so that your daily caloric need increases above your daily caloric intake. Simply said: eat less and move more. 
If you want to lose body fat, it is recommended to eat between 15 and 30% calories less than your daily caloric need. In order not to shock and block your metabolism, which is very contra-productive, always change your calorie intake gradually. I recommend you to do it in steps of 5 or 10% and letting your body adjust for at least a couple of weeks between consecutive changes. 
An average weight loss between 2 and 5 pounds (1 kg = 2.2 lbs) per month is best to reach a sustainable long-term result. Note that, as your body weight goes down, you will have to further decrease your daily calorie intake to stay below your new daily caloric need, and because your metabolism will gradually slow down during a calorie restricted diet. Daily calorie levels should never drop below 1200 calories for women or 1600 calories for men. 
When you finally have reached your target body weight, increase your calories very slowly (over a period of several months) back to your new daily caloric need. If you do it too fast, you will start gaining weight again, and might end up even fatter than you were before your diet. 
There exist four different kinds of nutrients that contain calories: protein, carbohydrates, fats, and alcohol. Let's take a closer look at them. 
Protein 

One gram of protein contains 4 calories. Sources of protein are: chicken, turkey, meat, fish, eggs, milk, yogurt, protein powder, nuts, beans, peas, and soy. Proteins from animals (meat, poultry, milk, fish) are more nutritious than proteins from plants (nuts, beans, peas, soy). 

Carbohydrates 
Carbohydrates (carbs or sugars) contain 4 calories per gram. Sources of carbohydrates are: potatoes, rice, pasta, table sugar, fruit, vegetables, bread, couscous, candy, sweet drinks, fruit juice, milk, cookies, chocolate, corn, cereals. 

Fats and oils 
Fats and oils contain 9 calories per gram. Sources of fats are: butter, oil, fat meat, fat fish, sausages, egg yolks, sauces, fat milk, cheese, cookies, fries, chips, nachos, nuts, chocolate. Fats from animals are worse for your cardiovascular health than oils from plants. 

Alcohol 
One gram (1 ml) of alcohol contains 7 calories. For example: 1 liter of sweet wine (15% alcohol, 15% sugar) contains 150 ml of alcohol (= 1050 calories) + 150 g of sugar (= 600 kcal) = 1650 calories per liter. As a comparison: non-fat milk contains only 340 calories per liter and orange juice contains 425 calories per liters. 
If you want to know the exact nutritional content of a food product, you can look it up on the internet. The USDA National Nutrient Database is a very good starting point. 
Eating Correctly 

Fats and oils 
Fats and oils are the worst nutrients for people who want to lose body fat. They contain the highest amount of calories (9) per gram, and the body stores them very easily as body fat. As fats contribute to the delicious taste of many food products, people usually tend to eat more if their meal contains lots of fat. Eat as little fat and oil as possible. 

Alcohol 
Alcohol has a very high caloric density of 7 calories per gram, and is easily converted into body fat. It is rather easy to drink relatively large quantities of it, and it invites to drink more as it tastes so well. One liter of sweet wine (15% alcohol, 15% sugar) contains 1650 calories. People who want to lose body fat should avoid drinking alcoholic drinks. 
Carbohydrates 
There exist several different kinds of carbohydrates. Some of them have a sweet taste, others not. All of them have their own characteristic glycemic index. The lower the glycemic index (GI), the lower the chance that they get stored as body fat. Let's take a closer look at some of the most important kinds of carbs. 

Glucose 
Glucose (also called dextrose) is a monosaccharide with a sweet taste that occurs a lot in products such as grapes, honey, and sweet fruits. Most carbohydrates that you eat are slowly transformed by the body into glucose during digestion. Glucose is the most important carbohydrate in the blood. If you eat products that contain lots of glucose, the glucose enters your blood almost immediately (GI>90), it is stored as body fat very easily as soon as there is too much glucose in the blood, and you become hungry again very fast. Products that contain lots of glucose must be avoided if you want to lose body fat. 

Sucrose 
Sucrose (table sugar) tastes about 33% sweeter than glucose and occurs in products such as white table sugar, honey, candy, jam, biscuits, chocolate, soft drinks, etc. Sucrose is a disaccharide that is split into glucose and fructose during digestion, and has a GI of about 75. Avoid products that contain lots of sucrose as much as possible. If you like soft drinks, pick the artificially sweetened ones that are sugar-free and contain zero calories. 

Fructose 
Fructose is the sweetest carbohydrate (about 70% sweeter than sucrose) and is the most important carb in fruits and some vegetables. This monosaccharide is converted into glucose very slowly and has a GI of about 20. Because fresh fruits mainly contain water and lots of fiber, it is fine to eat a few pieces of fruit every day. Don't eat too many grapes and other sweet fruits that contain too much glucose. Do not eat dried fruit and jam because they contain too much sugar per gram. Also don't drink any fruit juices (orange juice contains mostly glucose; apple juice contains mostly fructose). 
Lactose 
Lactose is the carb that occurs in milk and milk products, and it does not have a sweet taste. Lactose is a disaccharide that is split by the enzyme lactase into glucose and galactose during digestion. Lactose is a very good carb because it digests very slowly and has a low GI of about 45. This way, it is unlikely that is will be stored as body fat, and it takes a long time before you become hungry again. Drink only zero-fat milk and eat low-fat yogurt and cheese. Be careful, most cheese contains lots of fat. 
Complex carbs 
Complex carbs are basically long chains of glucose molecules, that mainly occur in products such as starch, maltodextrin, bread, pasta, rice, potatoes, corn, cereals, and vegetables. Complex carbs don't taste sweet. They digest rather fast into glucose (GI>80), especially when the products are cooked (not eaten raw) and/or contain little fiber. Don't eat too much bread, rice, potatoes, and pasta. It is better to eat uncooked vegetables because they contain lots of fiber that slows down the digestion. 

Protein 
Proteins are without doubt the best nutrient to eat for people who want to lose body fat. Eat as much as 1 gram of protein per pound of body weight (1 kg = 2.2 lbs). Proteins digest very slowly, they slow down the uptake of glucose in the blood, and they reduce the hunger feeling significantly. Proteins do not easily convert into body fat (the body burns about 1.5 calorie to convert 1 gram of protein into body fat. Therefore, 1 gram of protein can only be converted into 0.35 gram of fat). 
Protein is also an essential nutrient for maintaining your muscle mass during a low calorie diet. Be careful, egg yolks, cheese, milk, nuts, fish, and meat can contain lots of fat. Therefore it is better to chose products that are high in protein and low in fat, such as chicken and turkey breast, egg whites, non-fat milk, non-fat cheese and yogurt, low-fat fish and low-fat meat. Avoid chicken skin, sausages, hamburgers, and other meat products that are prepared with lots of fat or oil. Grill you meat and boil your eggs instead of baking them in butter or oil. 
Eat slowly digesting food 
It is important to eat mainly products that digest slowly (low glycemic index) because of two reasons. Because their nutrients are released more slowly into the blood stream, they are less likely to be converted into body fat. Secondly, it will take longer before you become hungry again. Protein, lactose and fructose are the best nutrients for a slow digestion. Foods that contain lots of fiber (dark bread, brown rice, fresh fruit, raw vegetables), and uncooked products also slow down the digestion. The longer you cook your products, the faster they will digest. 
Meals 
It is very important to eat at least 4 small meals per day, rather than 1 or 2 big meals. A couple of hours after a meal all food will be digested and all its nutrients are entered into the blood stream. If your blood is overloaded with nutrients (glucose, protein, fat) from a big meal, the body will start storing it as body fat. Moreover, by eating big meals, your stomach will become larger, resulting in a stronger hunger feeling. There are basically two things that result in a hunger feeling: an empty stomach and a low level of blood glucose (or other nutrients). Several small meals spread over the day keep your stomach smaller and keep your blood glucose level high enough throughout the day. 
Each of your meals should contain some protein and some carbs. Avoid fats, oils, sugar, and alcohol as much as possible. I would recommend you to eat at least 4 small meals per day, each of the same size. In the middle between each meal, drink a protein shake containing zero-fat milk and milk protein (casein) powder. Try to eat every day 2 grams of protein per kg of body weight, less than 30 grams of fat and oil, no sugar, and no alcohol. Drink at least 2 liter of water per day (the water in your tea, milk, and juice, obviously also counts). 

Recommended food products 
zero-fat milk, non-fat yogurt, non-fat cheese 
low-fat meat such as beef and horse 
low-fat fish such as tuna 
turkey and chicken breast without skin 
egg whites 
fresh fruits 
un-cooked vegetables, peas, and beans 
dark bread, brown rice, potatoes, dark pasta 
milk protein (calcium caseinate) powder 
water, sugar-free tea, zero calorie drinks 
Food products to be avoided 
fruit juice, dried fruit, grapes, honey, jam 
candy, cakes, biscuits, nuts, chips, nachos, fries 
fat meat, fat fish, egg yolks, sausages, hamburgers 
fat sauces, chocolate, sugar, butter, cream, oil 
white bread, white rice, white pasta 
alcoholic drinks such as wine, beer, vodka 
sugar containing drinks such as lemonade, cola 

Hunger Control 
These are some ways to manage the hunger feeling during a low calorie diet. 
Eat at least 4 small meals instead of 1 or 2 big meals. 
Eat foods that digest slowly (high in protein, lactose, fiber, raw vegetables and fruits). 
Drink and eat foods with a low caloric density (low number of calories per serving or per 100 grams). They fill your stomach while keeping your calorie intake low. 
Drink a zero-fat milk protein (casein) shake between your meals. 
Drink lots of water (or zero-calorie drinks) before, after, and between your meals. 
Avoid thinking about food. Be active, be busy, and avoid being bored. 
Avoid seeing and/or smelling delicious food. 
These are some tips to help you to avoid eating too much (bad food). 
Don't make it a habit to eat during other activities, such as watching TV, studying, etc. 
Avoid activities, social events, and places where people eat and drink lots of (bad) food, such as parties, restaurants, drinks, cinema, etc. 
Don't spend much time with people who have bad eating and drinking habits. 
Be outdoors and active. 
Don't grocery shop while being hungry, as you will more likely buy bad food. 
The more delicious your meals are, the more you will eat. Be careful. 
Physical Activity 
While reducing your daily calorie intake, and eating correctly are essential to be successful in losing body fat, your results will probably not be very impressive if your level of physical activity remains very low. Physical activity includes activities such as walking, working and sporting. Unless you are physically very active in your daily life, I recommend you to do at least 4 times per week some sport for about 1 hour. Two types of sport are particularly effective in helping you to reduce your body fat. 
Cardiovascular exercises 
Cardiovascular exercises specifically focus on burning calories by means of endurance exercises such as jogging (very strainful for your joints), swimming, cycling, or training on one of the cardio machines that you will find in your local gym: stationary bike, elliptical machine, stairclimber, treadmill, row machine, etc. Depending on the intensity these exercises can help you burn several hundreds of calories per hour. The best timing for cardiovascular training is in the morning, before your breakfast. That is because during the night, your body switches into fat burning mode, as the energy supply from food intake is no longer available. The best fat burning results are obtained while training at a heart beat rate between 130 and 165 beats per minute. 

Bodybuilding training 
While bodybuilding workouts also consume lots of energy, the main goal of bodybuilding is to increase the lean muscle mass. As the muscles are one of the main energy consumers in the body, having bigger muscles implies that the body burns more calories throughout the day, even during rest. A high protein diet in combination with bodybuilding training, is the best way to increase your lean muscle mass, and therefore to increase your daily caloric need. By combining bodybuilding with cardiovascular exercises, you will get without doubt the very best results. 
Tips and Tricks 
Don't eat during the first 2 hours of the day because your body is still in the fat burning mode of the night. Don't eat any fats and not too much carbs during the last 3 hours before you go to bed. During the night your body does not need much energy. Therefore, food eaten late at night will get stored as body fat during your sleep. A small amount of protein before going to bed is fine. 
Prepare your meals yourself so that you can control which ingredients go in. Meals from (fast food) restaurants contain usually too much fat. 
If you want to go through life with a certain body fat percentage, it is important never to let your body fat rise significantly above that level, because it is much easier to stay lean than it is to get lean. Your body will always easily slip back to its highest level of body fat, as it has some kind of memory. Approach it in a proactive preventative way rather than a reactive therapeutic way. 
Don't play yo-yo with your body weight. Keep your body fat constant once it is at the right level. Don't allow your calorie intake to jump up fast after a long period of dieting. It may take a long time (over 1 year) before your body is completely used to your new body composition. Finally your metabolism will find its new equilibrium and it will become easier to stay there. 
To be successful in losing body fat and staying lean, it is very important to be motivated, determined, devoted, disciplined, strict, and well organized in terms of planning your meals. 
How to follow your diet successfully 
Be motivated and determined. Ask yourself why you want to reduce your body fat, and how important it is to you. Less body fat makes you more beautiful and healthy. 
Change your mindset: stop thinking about food as an item of pleasure, consider its nutritional value as a means to feed your body, to get slim, and to stay healthy. 
Make sports a part of your life. Do your exercises every week on the same days and the same time. 
Allow yourself one junk day per week, on which you can eat whatever you want, without going above your daily calorie intake. The other 6 days you follow your diet very strictly. The junk day is very important from a psychological standpoint. 
Plan every morning when, what and how much you will eat that day. 
Eat every day around the same time. 
Don't make eating a big social event. Eat alone or with your family. 
Don't let other people decide or influence when, what, and how much you eat. You should be in control of your diet yourself. 
Don't buy or prepare more food than you are planning to eat. It's harder to stop eating when the table is still full of food. 
Leave the table as soon as you finish eating. 
Summary 
The following are the most important aspects for losing body fat: 
Eat fewer calories per day. 
Eat at least 4 small meals per day, equal in size. 
Eat and drink only products that are low in fat, oil, sugar, and alcohol. 
Eat and drink only slowly digesting products that contain lots of fiber, protein, water, lactose, fructose, and carbs with a low glycemic index. 
Eat lots of protein. 
Be physically active. Work, walk, exercise (cardiovascular and bodybuilding). 
The perfect fat loss day 
06:00: wake up 
06.30: cardiovascular training (about 45 minutes) 
08:00: breakfast 
10:00: zero-fat milk protein shake 
12:00: lunch 
14:00: zero-fat milk protein shake 
16:00: dinner 
17:00: bodybuilding training (about 45 minutes) 
18:00: small meal 
20:00: zero-fat milk protein shake 
22:00: bed time
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