If you're on a diet then eating out isn't generally the best option in the first place. You should be staying at home and preparing nutritionally-beneficial meals to complement whatever other measures you're taking to trim down.
Every now and then you're going to get called out for dinner, however, and when you do there are some things you can do to minimize the impacts on your body - not to mention some things you can do to completely ruin all your progress. Here's a listing of some of those restaurant options you'll want to avoid.
1.) The drive-thru. Drive-thrus SCREAM fast food, and you should be avoiding fast food at all pains. If the restaurant can prepare a meal in the time it takes to move your car from one side of the building to the other then you don't want to eat it in the first place, as any nutritional value the food may have once had has since been eradicated by deep fryers.
2.) The order-in. Not quite as bad as drive-thrus, depending on where you order from, but still bad. Ordering food over the phone usually indicates fast food as well, and again you want to avoid speedy delivery whenever possible. The most infamous of order-ins is probably the pizza, and a single large pizza can be enough to ruin several day's worth of progress on a diet, depending on what's topping it - and most pizza places that deliver don't offer the healthiest pizza choices.
3.) Buffets. Buffets are a mixed lot. Most offer a nice selection of vegetables that, while probably not of the highest quality, are still much healthier than the rest of their selection - food that's been coated in batter and deep fried. Avoid buffets when possible, especially if you don't have the willpower to avoid giant plates of breaded shrimp. And if you must go to one, minimize the number of plates of food you pack away, and balance your meat selections with plenty of greens and grains.
4.) High-calorie drinks. Okay, so you've made it successfully to a sit down restaurant. The drink you order alone can kill your diet. Normally you might think that alcohol is the worst offender in this category, and while it can be people gain the most pounds by ordering something heavy and creamy, like an ice cream float or a milkshake. When possible stick with water, as you'll not only save money you'll keep your waistline small.
4.) Greasy foods. Grease is the worst, and unfortunately most foods you order i a restaurant are laden with the stuff. Chicken wings and burgers are big offenders in this category. If possible try to order greens, and keep whatever salad dressing you have light. Barring greens you might want to try a nice pasta dish with a minimum of cheese to help balance out your food intake for the day.
5.) Dessert. It's so tempting to get dessert. Just look at those lovely pictures on the menu. Resist the urge, however: these desserts will turn your flat belly into a nice, big hill in no time, almost regardless of which one you choose.
Eating out need not be a major roadblock to maintaining a diet. You just need to keep your wits about you when you're ordering. And, if you take nothing else from this article, just remember one thing: NO FAST FOOD. You couldn't be making a worse choice for your belly when you go with fast food.