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Drinking Slim Fast shakes in place of meals can help you lose weight.
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With both canned shakes and shake mixes on their list of product offerings, SlimFast makes it easy to have a liquid meal replacement on the go. Despite the easy nutrition, you might find yourself experiencing unexpected side effects.

Read more: Pros and Cons for SlimFast

Substitute a Liquid Meal

Yes, you'll get a lot of nutrition, which can supplement or replace a meal, in a SlimFast shake, but your stomach might be growling at you a short time later. According to the SlimFast product website, the liquid is "packed with protein and fiber to keep you full for up to four hours."

"Up to" is the key phrase. Solid meals stay in the stomach for 20 to 30 minutes before slowly emptying over the course of a minimum of 1.5 hours. But a liquid meal can leave your belly as little as 30 minutes, according to the University of Colorado, leaving you fatigued, hungry and more likely to consume more calories later on.

One 325-milligram bottle of SlimFast Original Formula delivers 180 calories, keeping it below the recommended caloric count for a snack, according to Harvard Medical School. The organization advises keeping meal replacement calories down to 400, or approximately two bottles of SlimFast shake.

Read more: If I Just Drink Slim Fast Shakes, Can I Lose Weight More Quickly?

However, you don't want to eat a regular meal and then drink the supplement, warns Harvard. Doing so will likely result in your body getting too many calories, resulting in weight gain and the complications associated with it, such as diabetes and high blood pressure.

The school advises that meal replacement shakes should contain 10 to 20 grams per protein per 8-ounce serving. There should also be no more than 6 grams of fat or 40 grams of carbohydrates (including sugar).

Count Your Macros

SlimFast shakes come in four varieties: Original, Keto, Advanced Energy and Advanced Nutrition. The beverages come in 325-milliliter (11 ounce) bottles. Choose the formula that best fits your dietary plan, and log the macros into your food journal.


  • Calories — 180.
  • Fat — 5 grams, including 1 gram of saturated fat. The other 4 grams of fat come from canola oil, a polyunsaturated fat that contains Omega 3 fatty acids, according to Harvard T.H. Chan School of Public Health.
  • Carbohydrates — 25 grams, with 19 from sugar and 5 from dietary fiber.
  • Protein — 10 grams.


  • Calories — 180.
  • Fat — 14 grams, which is all saturated fat from MCT (medium-chain triglyceride oil from coconut).
  • Carbohydrates — 7 grams, with 5 grams of dietary fiber, resulting in 2 net grams of carbohydrates.
  • Protein — 8 grams.

Advanced Energy:

  • Calories — 180.
  • Fat — 9 grams, including 1.5 grams of saturated fat from milk protein concentrate.
  • Carbohydrates — 6 grams, including five from dietary fiber and one gram of sugar.
  • Protein — 20 grams

Advanced Nutrition:

  • Calories — 180.
  • Fat — 9 grams, including 1 gram of saturated fat from milk protein concentrate.
  • Carbohydrates — 7 grams, with 5 from dietary fiber and 1 gram of sugar.
  • Protein — 20 grams.

Know Potential Side Effects

Just because SlimFast shakes are chock-full of nutrition, and balanced in macronutrients, doesn't mean that you won't experience significant side effects from ingredients contained therein. There are a few to watch out for:

Sweeteners: Harvard Health recommends sticking to nutritional shakes where sugar is not listed as one of the top three ingredients. SlimFast Original has sugar as its third ingredient, and also contains fructose, high fructose corn syrup, and sucralose — an artificial sweetener derived from sugar, according to Harvard Medical School. Sucralose can cause bloating, diarrhea, migraines and other unpleasant symptoms in those who are sensitive to it, according to Michigan State University.

Stabilizers: Although it's not sugar, maltodextrin can raise your blood sugar levels significantly, according to a study published in the May 2019 edition of Nutrients. This ingredient is a relative of corn syrup solids, although with a dextrose equivalent (DE) of less than 20. The lower a sweetener is on the DE scale, the less sweet and thicker it is. Hence, it is used as a stabilizer for the shake's creamy texture. Another stabilizer in SlimFast is carrageenan, which is made from red seaweed, and generally considered to be safe and without side effects, according to the University of California.

Milk: If you're lactose intolerant, you'll want to avoid SlimFast shakes, as fat-free milk is the first ingredient. The product also contains milk protein concentrate. People unable to digest the milk sugar (lactose) due to a deficiency of the enzyme lactase will find it results in bloating, diarrhea and gas, according to the Mayo Clinic. Although it doesn't take a medical prescription to try a nutritional shake supplement such as SlimFast, it is always wise to talk to your doctor before making any dramatic changes to your diet.

Read more: How to Drink SlimFast Three Times a Day

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