During a Flex Meal (sometimes called a "free meal" or a "cheat meal"), you allow yourself to eat any of the foods that are forbidden on the rest of the diet.

For example, if you're on a low-carb diet you can eat extra carbs and starchy items like bread or pasta. If you've been following specific nutrient ratios, you ignore them. If you're eating low fat, you can eat french fries and pizza. Yes, you can even have dessert. The main idea is to address any cravings you might have

The great thing about a Flex Meal is that one meal isn't going to destroy your diet. Yet it's a big psychological advantage because:

You get built-in breaks for family gatherings, work events, or whatever goes on in your life that might disrupt your dieting plans.
You avoid feeling deprived of your favorite foods
It keeps your sanity by breaking up a strict diet
You don't have to worry about so-called "cheating" because you're doing it on purpose - it's a planned diversion

What's the catch?

You have to limit how often you do the Flex Meals, or it can stop your progress. You want to do them often enough to keep your sanity, but not so much that you don't end up losing any weight or stalling your weight beyond. It's also possible to abuse the meal itself in various ways (see rules below). (Remember the Energy Balance Principle)

Remember: The main purpose of a Flex Meal is to help you stick to your regular weight loss diet plan, so that you do in fact lose weight. If too many Flex Meals or abused Flex Meals stops that progress, obviously it's a useless tactic.

How Often?

We suggest incorporating 1 or 2 Flex Meals per week into your program. They should not be on consecutive days.

There are a few exceptions:

If you are overweight and trying to avoid "Trigger Foods" that contributed to your weight problem, consider waiting for 3 to 6 weeks before starting Flex Meals. We're assuming you'll want to eat those trigger foods during the meal and that will throw you off track. In contrast, if you wait for 3 to 6 weeks, your taste preferences will change and adapt, and your powerful taste for those foods will diminish allowing you to introduce them without them controlling you.
If you're on a short diet (e.g., 2 weeks or so), Flex Meals aren't as necessary. You can probably handle the diet psychologically without them... but it's your choice.

2 Meal Rules

During the meal itself, there are two helpful rules:

No gorging: If you are deliberately attempting to eat as much as you possibly can, or if you eat yourself sick (as if you'll never have another meal again) you're abusing the purpose and reducing the results you achieved during the week. Eat for some pleasure, enjoyment, and to get full and satisfied ...and you'll be fine.
The meal should also be done in one sitting and not consumed over several hours. Consider limiting it to around 1 hour.

In other words, the meal should be less about how MUCH you eat, and more about WHAT you eat (eating the various foods you've been deprived of and enjoy).

If you find it hard to follow those two rules because you've been starving or thinking and dreaming constantly about food during the week, then Flex Meals aren't going to be the solution -- you probably need to make some other significant adjustments to your weight loss program.

Useful Guidelines

Here are several guidelines to help keep you on track while you enjoy your Flex Meals to the fullest.

A Flex Meal is less likely to backfire on you start with a healthy base meal (a source of protein and a salad for instance), and then add those extra forbidden foods to it. In other words, don't toss out all your nutritional sense for this meal.
Space out your Flex Meals as far as possible. If you want one Flex Meal a week, try to space them seven days apart. If you want two Flex Meals a week, try to space them at least three days apart.
Eat your Flex Meal as dinner. If you eat it for breakfast or lunch, it can be psychologically difficult to go back to the diet the rest of the day.
Eat your Flex Meal out of the house. It feels more like a reward and it's less likely to turn into a long binge session. The Flex Meal ends when you leave the restaurant--leave uneaten food at the restaurant, or package up shareable items for someone else not on the diet. If you eat your Flex Meal at home, eat it all in one sitting, then clean up and get busy with something other than food.
Eat your Flex Meal on an exercise day, if possible. Not only does this help reduce any hunger caused by exercise, it also provides your body extra energy to recover from your workout. (You may want to eat a little before the workout, and the rest of it after your workout.)
Savor your Flex Meals. Take your time. Eat slowly and relish the flavors of all these foods you can't eat during the rest of the diet.

Weight gain will come off. Your weight will probably spike after a Flex Meal, especially if you consume lots of carbohydrates. This is normal. It's mostly water weight and it'll come off rapidly over the next couple of days.