Side Effects of Slim Fast

Slim Fast

If you are considering the Slim Fast diet program, be aware of the possible side effects in order to decide if this is the program for you. There are some unpleasant side effects to drinking the shakes and eating the meal replacement bars, but many find that they are not troublesome enough to abandon the use of the products altogether. The side effects can range from headaches to bloating, and some even feel tired while on this plan.

Short-Term Side Effects of Slim Fast Diets

The purpose of Slim Fast shakes and nutrition bars is to replace two daily meals with lower-calorie substitutes. Unfortunately, many dieters rely on the meal-replacement products alone, resulting in a very restricted caloric intake, rapid weight loss, nutritional deficiencies, and health complications. Most side effects are temporary and will cease as the body adjusts to the diet.

Transient side effects of using Slim Fast include the following:

  • Constipation
  • Headache
  • Loose stools
  • Intense hunger
  • Gas and bloating
  • Abdominal discomfort

These side effects typically disappear with continued use of the shakes and bars, but may persist in some people. Dieters who are lactose intolerant may experience significant bloating and gas while using milk-based Slim Fast shakes.

Potentially Serious Side Effects

Serious side effects are typically a result of rapid weight loss, and rarely occur with proper use of the product. Some dieters report hair loss, gallstones, low blood pressure, abnormal blood glucose levels, abnormal QT intervals, ECG abnormalities, and cessation of menstruation.

Using the shakes and nutrition bars as directed will generally not reduce your total daily caloric intake to a dangerous level. However, if your dinner meal is inadequate in the amount of calories or nutrients it provides, you may experience potentially dangerous side effects to Slim Fast.

Health Complications

Doctors often recommend low-calorie and very low-calorie diets to obese patients at risk for weight-related health complications, such as diabetes, high cholesterol, and high blood pressure. When used as directed and under medical supervision, these diets are very beneficial. However, the National Institute of Diabetes and Digestive and Kidney Diseases warns that these diets can be dangerous when used by mildly or moderately overweight dieters.

Gallbladder Disease

Gallbladder disease is the most common severe side effect associated with rapid weight loss. According to the University of Maryland Medical Center, rapid weight loss increases the production of cholesterol by the liver, resulting in super saturation and an increased risk of gallstones. Losing more than 3 pounds per week impairs functioning of the gallbladder, decreasing its ability to contract and expel bile. This risk is as high as 12 percent following 8 to 16 weeks on a restricted-calorie diet.


Replacing meals with Slim Fast shakes may result in fatigue or feeling weak. This is because the body will have fewer calories available for use.

Stomach Problems

Slim Fast may upset the stomach of some people. This can be due to the change in diet or to the artificial sweeteners used in some types of Slim Fast.

Weight Gain and Fluctuation

Slim Fast only helps with weight loss if the user eliminates more normal food calories from their diet than the shakes contain. If shakes are consumed in addition to a normal diet, they can contribute to weight gain.

Using the products as directed can promote weight loss, but unless reduced calorie levels are sustained, weight can easily return.


Slim Fast may cause feelings of hunger since the body may demand more calorie intake. The body often adjusts to reduced calorie intake over time

Muscle Loss

While very low-calorie diets cause considerable loss of fat, they also cause dangerous muscle loss. Moreover, it is very difficult to maintain weight loss once eating habits return to normal. Unless you commit to healthy eating, engage in regular exercise, and change your lifestyle, you will very likely regain the pounds you shed during your diet.

Seek Doctor's Advice

If you are using Slim Fast products and experience any severe side effects, you should seek the advice of your doctor before continuing the use of these products. To ensure your weight loss attempt is successful, consult your doctor before beginning any new diet program and follow the program guidelines carefully.

Minimal Risk of Side Effects

Short-term use of meal-replacement products can help jump-start a weight loss program and offer a convenient way to shed a few pounds. When used as directed, Slim Fast provides numerous health benefits with minimal risk of side effects.

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Side Effects of Slim Fast