With soy protein. Simply replace one meal a day with a delicious, healthy Slim Fast shake. Walk or exercise 30 minutes a day and eat sensibly, including lots of fruits and vegetables. Slim Fast shakes give you the healthy nutrition of a balanced meal with only 1.5 grams of fat and 220 calories. Many people enjoy a delicious Slim Fast shake, a piece of fruit and a cup of coffee or non-caloric beverage in place of a meal.