What kind of exercise did you do, at what intensity, and for how long?
The creator of Soylent will be the first to tell you this (he works out quite a bit).
Weight loss is deceptively simple. Take in less calories per day than you burn, and you will lose weight. That's it. "Types" of calories is important too but is focused on too much. Exercise is very important, but trying to lose weight via exercise is ridiculous. It's much easier to just not intake those calories in the first place.
There are calculators that will help you to figure your BMR (basal metabolic rate) which will allow you to figure out the corresponding amount of caloric intake you can have that will allow you to have a net caloric "loss".
Actually putting this into practice does involve meticulous calorie counting and very probably feeling hungry a lot of the time, as you are used to a higher caloric intake; that is where the "deceptive" bit comes in.
Soylent has none of the complex/unnecessary/unhealthy chemical substances tradional diets (milk,bread,nuts,fish) have that are the frequent object of intolerances.
One of the key "milk" allergies is allergy to whey, which from what has been posted in this thread is the protein source for Soylent..
In his blogs he mentioned that in his head this could ultimately be a drink tailormade for your specific needs, so someone with whey allergy could swap the whey proteins for meat or fish proteins (if those are readibly available at all)
