If you subsist on fast food, you're obviously on your way to health problems, but those problems might not include malnutrition because even fast food inputs are complex compared to something engineered from the most primitive possible inputs to specific macronutrient ratios.

> Soylent could be a very positive change for those people.

It could also be worse. Without long-term, scientifically valid studies, no one knows for sure.

> It's not like meals are an arcane science working some unknown magic on your body, it's about biological needs and chemistry.

The workings of the body are not fully known, even today. There are many unknowns in nutrition, which is precisely why none of the pharmaceutical companies have a "replace all meals!" product.

Believe it or not, if you're eating a variety of junkfood you are probably not on the road to malnutrition. A diverse diet of pretty much any quality of food is likely to get you every nutrient you need, including the ones we don't understand. Most of the cases of people getting malnutrition from junk food seem to be from people who do something like eating nothing but ramen dry packs every day. I think that's usually part of an eating disorder, as people tend to get bored of the same food all the time.

This is why the concept of a general meal replacement (as opposed to an occasional meal replacement) is scary. It has absolutely no diversity. If it's missing something it's missing it for every meal, and it takes a long time to find out that something's missing.

> And it's not like there are chefs cooking healthy food in every home.

You don't need a chef to quickly cook healthy food at home. In fact, most chefs tend to overcomplicate food by aiming for taste instead of healthiness.

Throw some vegetables in the steamer, add some tofu and in five minutes you got yourself a healthy lunch. This is just one example.

> An ensure contains a mere 11% of your daily potassium for example.

If you are referring to Ensure Complete, (rather than regular Ensure, which is not intended as a complete replacement), it may be low in potassium because complete replacements may be used by people with various medical conditions for which reduced potassium intake, below the usual-stated Adequate Intake, is recommended [1] (its possible for other users to supplement potassium, so that design choice would make it more broadly usable.)

Nutrition is more than one-size-fits-all values.

[1] See, e.g., the special considerations that apply to Potassium here: http://www.iom.edu/Global/News%20Announcements/~/media/442A0...