Slim Fast: Fad Diet or Evidence-Based Weight Loss Tool?

I mention Slim Fast but what I really mean is any product that could be considered a “meal replacement” or a single nutritionally balanced item that you can consume in lieu of a formal meal.  Meal replacements come in the form of shakes, meal bars, or even a bowl of cereal.  Some are high-protein, while others are balanced in protein and carbs.  The typical routine is to consume 2 meal replacements per day, one instead of breakfast and one instead of lunch.  Slim Fast came onto the market originally back in the 70’s, but the concept has held steady all these years and now a huge variety of options are available across multiple companies.

Should you ever use meal replacements in your weight loss plan?

Let’s take a look at the research.  You might be surprised that a great deal of research shows that meal replacements can increase your weight loss potential. A meta-analysis of 6 studies showed that meal replacements produced 6-7 lbs more weight loss than a typical weight loss diet (Heymsfield et al 2003). A recent study found that people who used just 1 shake per day for lunch consumed fewer calories and lost a significant amount of weight compared to when they followed their usual diets (Levitsky et al 2011). Another study compared liquid versus solid meal replacements and found that solid meal replacements had a stronger impact on appetite control (Martens et al 2010). Also, some of the largest weight loss studies routinely use meal replacements in conjunction with a formal lifestyle intervention.  In general, meal replacements work by enforcing portion control, limiting calories at these meals, and taking the work out of food selection and preparation.  An important thing to note is that meal replacements are typically used along with healthy diet and exercise.

When To Consider Using Meal Replacements?

The best time to use meal replacements is during the following circumstances:

–>  A weight loss plateau

–> To jump start weight loss if the pounds are coming off too slowly (i.e., less than 1 pound per week)

–> When you feel your eating is getting out of control

–> When you are too busy to fix a healthy breakfast or lunch

–> When you need a break from diet journaling

In these circumstances I suggest using meal replacements for 2 weeks at a time for 2 meals per day, then reducing to 1 meal per day for 1 week, and then back to portion control with mixed foods.  Think of meal replacements as a yet another tool in your toolbox to help you through a rough spot.

Which product do I recommend?

Use the product you like best, because after all, you’ll have to live with it for 2 meals a day for a while. You might try a few, including shakes, bars, or a cereal.  If you go with cereal be sure to measure or for ease, buy the single serving cups.   My one caution is to be sure the product isn’t too high in sugar, so for example, I would not choose Lucky Charms for a meal replacement.  Find a product that is nutritionally balanced and keep in mind that adequate amounts of fiber and/or protein can help regulate appetite.

Bottom line:  Slim Fast and other meal replacements are not fad diets.  These are helpful weight loss tools with plenty of evidence to support their use while you are following a healthy lifestyle plan.  If you are struggling with your weight loss, definitely consider shaking things up!



Martens et al (2011)  A solid high-protein meal evokes stronger hunger suppression than a liquefied high-protein meal.  Obesity, 19(3), 522-527.

Heymsfield, SB et al (2003).  Weight management using a meal replacement strategy:  Meta and pooling analysis from six studies.  International Journal of Obesity, 27, 537-549.

Levitsky et al (2011). Losing weight without dieting: Use of commercial foods as meal replacements for lunch produces an extended energy deficit.  Appetite, 57, 211-217.

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  1. Mbfgmike says:

    I know I use a meal bar on a busy day when rushing from appointment to appointment. It beats being stuck going to the drive through well hungry & getting a burger and fries.
    No Lucky Charms?? Didn’t anyone tell you they were magically delicious??

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