Earlier quoted context omitted.
Slimfast has 4x as much sugar as Soylent (per-calorie). To get 2000 calories from Slimfast you'd be getting 180g sugar, while with Soylent it would be 45g. Now 45g is a little higher than recommended, but 180g is way too high. http://d8m5oga7foiu.cloudfront.net/wp-content/uploads/2016/1... http://files.soylent.com/pdf/soylent-drink-nutrition-facts-e...
not sure where you got the slimfast nutritional info but they have 1g of sugar: http://slimfast.com/advanced-nutrition/#shakes if it had that much sugar, it wouldve never gained a reputation for losing weight.
Ah, I see you've forgotten about the 'low-fat' era.
Efficacy has very little to do with the popularity of diets.