What you eat really matters when trying to lose weight. Quality calories should be your goal. Junk food, like chips, donuts and sodas aren't nutritious and have loads of calories. They also have you wanting to eat more in just a short time. Control your eating with a nutrition plan and food journal.
We are kings and queens of "too large" servings of food and that's without even "super-sizing" anything! Keep your daily food journal to track what, how much and why you are eating. This will help you with portion control.
Pack your lunches and snacks instead of eating out at work. If you eat at a restaurant for dinner, check out the menu online so you know what to order. Most restaurants now have a "healthy foods" menu. One way to eat quality calories is to "eat your calories" instead of "drinking your calories." When you eat food, you have more satiety and you are more likely to take in fewer calories.
Another way to control calorie intake is to eat more water based foods (volume eating). The basics of volume eating is to eat as many foods with high water content/low calories as you can. Foods such as fresh fruits and vegetables are examples. These types of foods help you to feel fuller (satiety) while eating fewer calories.
For instance, grapes with the same calorie amount as raisins will provide more satiety and theoretically help you eat less the rest of the day. Also, the energy density of food is a key component when trying to add volume to your diet. Energy density (ED) is defined as the amount of calories of a food divided by its weight in grams.
You should basically focus on foods rich in fiber with high water content (or low ED value). Fresh fruits (apples, etc.) and vegetables (such as tomatoes and broccoli) whole grain pastas, rice, whole grain breads and cereals, soups, salads and skinless white chicken/turkey are some examples.
Other dryer foods could be added to your diet on a limited basis. Dryer foods would be starchy fruits and vegetables, salad dressings, crackers, etc.
The old rule still applies: a caloric surplus (consume more calories than you burn) will cause you to gain weight.