SlimFast is an American company headquartered in Palm Beach Gardens, Florida, that markets an eponymous brand of shakes, bars, snacks, packaged meals, and other dietary supplement foods sold in the U.S., Canada, France, Germany, Iceland, Ireland, Latin America, and the U.K. SlimFast promotes diets and weight loss plans featuring its food products.

The product was rolled out nationwide in a marketing campaign that began on July 11, 1977 for "a fat-free, carbohydrate-free, animal-based fortified cherry-flavored protein supplement formula" that promised to make purchasers "feel better, cleaner, stronger and healthier.

[6] After the sale, KSF Acquisition invested with Kainos Capital in order to take responsibility for the SlimFast brand in the UK, Ireland and Germany.

[12] In a 2009 study involving 300 overweight and obese males and females aged 21–60 years published by Cambridge University Press, the SlimFast programme achieved weight losses of between 5 kg (11 lbs) and 9 kg (19 lbs) after six months compared to a control diet.

The results were comparable to that of both the Weight Watchers 'Pure Points' programme and Rosemary Conley's 'Eat yourself Slim' Diet and Fitness Plan.