Updated October 17, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Meal replacements are calorie and portion controlled beverages or food items, such as bars or shakes, that can be used as a substitution for food. The American Academy of Nutrition and Dietetics states, "meal replacements containing a known energy and macronutrient are a useful strategy to eliminate problematic foods choices and/or complex meal planning while trying to achieve a 500 to 1,000 energy deficit." This is the estimated amount of calories you would need to cut or burn to lose about 1/2 pound to 1 pound per week.

The Academy's weight loss position papers also report several studies that have shown equivalent or greater weight loss results when using meal replacements as opposed to reduced energy diet plans. Studies have also shown that those persons with Type 2 diabetes lose about 7 percent of their body weight in one year and consistently report medication reductions when using meal replacements. In these studies, though, people were still exercising, keeping food diaries and learning about nutrition. 

How Can You Use Meal Replacements? 

1. Keep it to a Minimum: If you are going to use a meal replacement to lose weight, don't abuse it. Aim to supplement one to two meals maximum and possible one snack daily. It is still important to learn how to eat because using meal replacements forever is not sustainable. 

2. Use as a Substitution: Adding a meal replacement to your diet plan without eliminating calories somewhere else will have opposite results - weight gain. My advice is to use your meal replacement when you feel the most vulnerable or when you tend to overeat.

For example, if you typically go out for lunch and overeat at this meal daily, then picking a meal replacement for this particular meal might help you to improve your blood sugars, reduce calories and jump start weight loss. 

3. Learn How to Eat Balanced: Some meal replacements, especially shakes, lack one thing - there is no chewing involved during ingestion. Satisfaction can be found from chewing. Also, whole foods take longer to metabolize because the body has to work extra to break them down. Therefore, it's important to learn how to eat balanced meals because you probably won't use meal replacements forever. Learning how to eat balanced meals can help you to adapt a healthy lifestyle, keep weight off and boost your nutrition. Balanced eating includes lean protein, healthy fat, fiber and some complex carbohydrate.

Think about your plate. For instance, use a smaller plate, 9" if possible - this will give the illusion of eating more food. Secondly, aim to make 1/2 your plate non-starchy vegetables which contain fewer calories and carbohydrate, but have filling power. Non-starchy vegetables are also rich in water, fiber, vitamins and minerals. Thirdly, aim to make 1/4 of your plate lean protein - white meat chicken, turkey, fish, lean beef. Finally, the last 1/4 of your plate is dedicated to a complex carbohydrate - 1 small sweet potato (the size of a computer mouse), 1 cup of beans, or 1 cup of quinoa (about a fist full). Generally, you can use the fist as a guiding point for carbohydrate portion control. It is very important to monitor carbohydrate intake because this is the macronutrient that is going to impact blood sugars the most.

4. Know What to Look For: When choosing a meal replacement shake, aim to choose one with limited added sugars. Depending on your calorie needs, a meal replacement shake should be about 300-500 calories, at maximum. The idea is that a meal replacement will yield a calorie deficit and help you to lose weight. 

Aim to keep your meal replacement shake to about 30-45 g of carbohydrate. You also want your meal replacement to have at least 3 g of fiber, which will help to keep you full and slow down the rate at which blood sugars rise. Commercial meal replacements with resistant starch or modified maltodextrin are digested more slowly than refined carbohydrate ingredients, which may help with blood sugar control. 

5. Make Your Own: A great way to control calories, ingredients and sugar is to make your own meal replacement shake. You can use a protein powder such as whey protein, hemp protein or soy protein (if you are vegetarian) and add a serving of milk (or low-fat Greek yogurt to reduce carbohydrate intake) and fruit. I also like to tell my patients to add ground flaxseed meal or chia seed to boost healthy fat and fiber intake. If you don't like the consistency using ground flax or chia you can use almond, peanut, or sunbutter. 

An example shake would be: 

1 scoop of whey protein powder or soy protein or hemp protein (not all protein powders are created equal. Aim to choose one with little sugar and choose one that is the purest in nature) 

1/2 small container (3.5 ounces) of low-fat plain or vanilla Greek yogurt

4 oz of skim milk 

3/4 cup of frozen blueberries 

4 oz of water

3-4 ice cubes

1 teaspoon all natural or organic almond butter (you can substitute for sunbutter, cashew or peanut butter)

*Add a probiotic to help promote digestive health

*Recipe calculated using 100% pure unflavored soy protein powder, 1/2 container low-fat plain Greek yogurt and 1 tablespoon all natural almond butter 

Nutrition Content:

Calories 365 calories, 8 g fat 1.5 g saturated fat, 13 mg cholesterol, 463 mg sodium, 819 mg potassium, 37.5 g carbohydrate, 8 g fiber, 18 g sugar, 41 g protein

*To reduce carbohydrate content you can eliminate the milk and you will save 6 g carbohydrate and 6 g sugar

*All of the sugar content in this recipe is coming from milk and fruit. There is no added sugar. 

Resources: 

J Am Diet Assoc. Position of the American Dietetic Association: Weight Management. 2009;109:330-346. 

Verdi, Cassandra. Making a meal of it; lower-calorie shakes or bars can be part of a safe weight loss plan. Diabetes Forecast. October 2014; 62-63. 

CalorieCount. Accessed on-line. September 30, 2014: Caloriecount.D106