Even Soylent is healthier than the typical western diet. I spent 2 weeks on Soylent and my health improved quiet a bit surprisingly.
That said I don't even eat the American diet, but I suppose if I had to choose between a life of American diet of fried chicken and hamburgers vs drink Soylent it would be easier to drink Soylent (probably healthier too). And that says something about just how bad fast food is where if you live a month on fast food your health will dramatically decline dangerously.
Look at this survey. How bad american healthcare is :( This is so sad. http://www.commonwealthfund.org/publications/fund-reports/2014/jun/mirror-mirror