[fasouto]

Your basic premise is wrong they are not the same thing at all. Soylent doesn't replace a meal, it is a meal with all the nutrients. Slimfast was designed to supplement food to lose weight. The nutritional aspects of each are totally different.

[kaitai]

SlimFast is designed to "supplement" food in that they suggest you replace two meals a day with it. The difference is that SlimFast doesn't suggest replacing three meals.