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The Promise

This isn't a 4-day crash diet. It's actually a monthlong program that you tackle in 4-day bursts. And you can do anything for only 4 days at a time, right?

Before you start dieting with the 4-Day Diet by Ian Smith, MD, there's a little up-front work. You keep a food diary and record your exercise and your mood for 10 days before you even start the diet.

You also do a little self-evaluation, trying to figure out why you're overweight, why you've had problems losing weight, and what your challenges are.

Once you set a weight-loss goal, you start the actual diet. The diet is made up of seven phases that each last 4 days. Each phase has a different focus with lots of food choices, so you shouldn't get bored.

The seven phases go like this:

  1. Induction: This first phase is about getting rid of toxins by eating mostly fruits, vegetables, beans, and legumes.
  2. Transition: You start reintroducing foods without overdoing it.
  3. Protein Stretch: You’ll load up on protein, such as lean meats, fish, and eggs.
  4. Smooth: This is where you can "cheat" a little. You can add some pizza, pasta, burgers, or hot dogs. Just don't pig out.
  5. Push: This is a hard part. You’ll need all your mental energy to get through these 4 days of limited calories and at least an hour of cardio a day.
  6. Pace: You keep a steady exercise and balanced diet going.
  7. Vigorous: This one is the strictest part -- 4 days of mostly vegetables and fruit, plus lots of cardio.

What You Can Eat and What You Can't

Food choices vary between stages, but Smith keeps things simple with a list of foods and portions you can eat each day. Eat until you are satisfied but not stuffed.

The 4 Day Diet doesn’t say much about alcohol, other than it’s a temptation and you should practice the 80-20 rule. That means that if 80% of what you eat and drink is healthy and on the plan, and the remaining 20% is off the plan, you will still succeed in losing weight.

Level of Effort: Medium

Limitations: You may make smart substitutions for some of the foods on your daily list, but generally, you can’t eat high-fat, high-carb foods.

Cooking and shopping: You’ll cook or eat out as usual, as long as you stick to the guidelines.

Packaged foods or meals: No.

In-person meetings: No.

Exercise: Required. Each day has specific exercise goals including cardio, strength, and resistance training, ranging from about 40 to 70 minutes per day, excluding the occasional rest day.

Does It Allow for Dietary Restrictions or Preferences?

The 4 Day Diet is generally geared toward low-fat, low-salt foods. You can easily adjust it to meet gluten-free, vegetarian, or vegan needs.

What Else You Should Know

Cost: You’ll spend roughly the same amount on groceries.

Support: No.

What Dr. Melinda Ratini Says:

Does It Work?

Though there has been no specific research done on the 4 Day Diet, some aspects of the plan have been well studied. Weight loss is very likely whenever you restrict your calories, and the 4 Day Diet cuts calories in almost all of the seven phases.

There is no science, however, that says 4-day blocks of alternating restrictions will work any better for weight loss. On the other hand, certain behavioral strategies, like keeping a food diary, have been shown to help both long- and short-term weight loss.

Is It Good for Certain Conditions?

The 4 Day Diet fosters weight loss by choosing foods that are low in salt, fat, and carbs. This type of diet promotes heart health by helping lower cholesterol and blood pressure.

Weight loss and exercise are the two keys to preventing diabetes. But if you are already being treated for diabetes, an alternating diet may leave you with dangerously low blood sugars. You have to clear this diet with your doctor before trying it out.

The Final Word

In theory, this should be an easy diet plan to follow. It has simple instructions and includes foods that are easy to buy and prepare.

But in practice, this is going to be a hard plan to stick with.

It will take a lot of determination and willpower to make it through even 4 days of some of these phases. Choices and amounts are limited. And you will need to find time in your busy day for the food prep and the exercise.

This diet plan includes a very challenging exercise requirement that will definitely help with weight loss but may be too ambitious for someone who has been inactive or has a medical problem. Check with your doctor first.

WebMD Diet A-Z

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