Do These Age-Old Diet Shakes Work At All?

May 5, 2017
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SlimFast Review

SlimFast may be one of the most recognized names when it comes to weight loss shakes. Since 1987, these shakes have been sold in grocery stores as a way to help people safely lose weight. However, though the brand makes lofty claims about the effectiveness and health benefits of its products, we’re skeptical about whether it truly is a smart dieting choice. This review will examine the hard facts of Slim Fast shakes’ ingredients, including the logic behind concerns with specific ingredients. We’ll also compare the diet shakes to basic nutritional standards to put everything in context. Our goal is to help you understand SlimFast better from a factual standpoint so you can decide whether it’s right for you.

SlimFast Nutritional Facts

At first glance, the nutrition label on that back of SlimFast’s bottle sets off a few warning bells. The ingredients list is lengthy and features no fewer than six items we consider controversial and harmful to your health (see the next section for more details!).



On looking at the nutrition facts, the first thing we noticed was the calorie count. Just one of these little 11-ounce beverages has 190 calories. While this is an OK number for meal replacement shake, when you weigh that number against the other nutritional benefits of the shake, it comes down to a lot of calories for not much benefit. The ratio of those calories that come from fat is high, as is the amount of sodium when compared to other weight loss shakes.

One of the worst aspects of SlimFast’s nutritional panel, though, is the amount of sugar it contains. 18 grams is higher than just about any other healthy weight-loss shake out there. Sugar does not promote weight loss, and so much of it in a product calls into question where that sugar comes from.


Controversial Ingredients

Like we said, the label contains five ingredients and one claim we consider questionable at best.

Maltodextrin is a food additive used as a thickener[i]. While it’s technically “natural” (derived from corn, rice, potato, or wheat starch), it’s an incredible processed ingredient often used together with artificial sweeteners.

“Natural & Artificial Flavor” is a confusing term unregulated by the FDA[ii]. While there may be natural components in these flavorings, they are processed and often contain synthetic ingredients. A “flavor” according to the FDA is an ingredient “whose significant function in food is flavoring rather than nutritional.”[iii] These flavors are generally created from starches and contain chemicals that pose potential harm to our health.

Monoglycerides and diglycerides are also food additives containing high amounts of trans fats, the most unhealthy form of fat we can eat. Even though the FDA requires labeling trans fat content[iv], this rule doesn’t apply to emulsifiers (which is what mono- and diglycerides are). Basically, this means that by using monoglycerides and diglycerides, a food can contain trans fat without the manufacturer having to admit it on their nutrition label.

Sucralose is also known as Splenda. This artificial sweetener is calorie-free, making it popular in diet and weight loss food products. However, it contains dangerous organocholorine compounds the human body cannot detoxify[v]. While the FDA claims the body only absorbs up 27% of these toxins, a Japanese study found that number to be closer to 40%[vi].

Carrageenan is a natural thickening substance that comes from red seaweed. It’s most often used to keep beverages from separating and to make low-fat foods taste better[vii].

Finally, SlimFast’s label claims the product is lactose free, and yet the second ingredient listed is milk protein concentrate. A asterisk at the bottom of their website qualifies this claim by saying their product is “99.8% lactose free.”[viii]


Protein Sources (Core Engine)

All of the protein in SlimFast’s diet shakes come from milk protein concentrate (MPC). Derived from milk, MPC is a complete protein made up of casein and whey proteins in similar ratios to regular milk[ix]. The disappointing thing about the protein in SlimFast is how low the number is. There aren’t many shakes advertised as “protein shakes” that have fewer grams of protein per serving than the SlimFast shake. While it at least makes it to the double digits, a good protein shake will have closer to 15 grams per serving. The company does, however, offer an “Advanced” version of the meal replacement shake that contains 20 grams of protein and less sugar at the cost of increasing the amount of fat.


Fiber Sources

With 5 grams of fiber, SlimFast has a passable amount that is likely to improve satiety and keep you full. However, this number is low compared to other weight loss shakes available.


What Are the Sweeteners?

Sucralose – also called Splenda – is the artificial sweetener used in SlimFast shakes. It’s made by chlorinating regular table sugar, and that process is what makes sucralose so harmful. Since the human body can’t rid itself of all the sucralose it ingests, the sucralose begins to concentrate in the liver, kidney, and gastrointestinal tract[x]. There it sits, collecting, slowly but surely negatively impacting your health.

Aside from the fact it’s made with an artificial sweetener, SlimFast shakes have so much sugar in them it’s hard to view the shakes as healthy. In fact, 18 grams is almost half of the amount of sugar fond in your average can of soda.


Who’s Behind SlimFast?

SlimFast began in 1977 as a product under the Thompson Medical Company. Ten years later, the product became a private company that was eventually bought by Unilever and then sold to Kainos Capital in 2014[xi].


Side Effects

Sucralose is a cancer-causing carcinogen also known to cause birth defects and immune dysfunction[xii]. Additional studies have shown sucralose to be the culprit of shrinkage in the thymus gland, enlarged liver and kidneys, and a reduced growth rate.

Monoglycerides and diglycerides contain trans fats, which play a role in increasing the risk of serious health issues. Trans fats can be to blame for diseases such as heart disease, stroke, and diabetes. Health concerns like inflammation, obesity, and high cholesterol levels have also been traced back to trans fats[xiii].

Carrageenan has no nutritional value and has been accused of causing inflammation, cancer, and especially gut problems. Our digestive system’s response to carrageenan is similar to the response our bodies have to pathogens like Salmonella[xiv].


How to Contact

SlimFast’s website has very little information on it about the company itself. The only way to contact the company seems to be through their social media.


Product Returns

The company’s website does not list a return policy or customer satisfaction policy that we could locate at the time of this review. The company has an average rating of 2 out of 5 stars on Consumer Affairs, and does not participate in the accreditation program[xv].


Other Products by SlimFast

In addition to the pre-bottled shakes, SlimFast also has a shake powder. The bottled shakes technically come in 7 flavors, but in reality it’s 3 chocolate variations and 2 vanilla variations alongside cappuccino and strawberries and cream. The company also offers:

  • Meal replacement bars
  • Snack bars
  • 100-calorie snack pack


Does it Work?

SlimFast’s diet shakes are part of their “2-1-3” plan which advises replacing 2 meals a day with a shake, eating 1 500-calorie meal, and eating 3 100-calorie snacks[xvi]. Sticking closely to this plan means you’ll be eating around 1200 calories a day, which is low enough that you probably will lose weight. However, that’s only if you stick to their “2-1-3” plan.

Using just the shakes by themselves doesn’t seem likely to promote any notable weight loss. Aside from that, the ingredient concerns and lack of more protein and fiber make this shake average at best.