I happened to see this paper, which may be of interest to those experimenting with Soylent. The title is "Long-term feeding on powdered food causes hyperglycemia and signs of systemic illness in mice".
They fed different batches of mice the same food, except that one was in the usual pellet form and one was powdered and needed no chewing. They also tested both short- and long-term feeding on powdered food. Their conclusion:
The hyperglycemia associated with long-term powdered-food feeding may lead to certain systemic illness signs, such as elevations of blood glucose, hypertension, and abnormal behaviors in mice. Mastication of food of adequate hardness may be very important for the maintenance of systemic (physical and mental) health, possibly via reduction in the levels of blood glucose and/or adrenal stress hormones (catecholamines and glucocorticoids).
Missing masticatory stress is also discussed here:
https://groups.google.com/forum/#!topic/less-wrong-parents/EF3CE9JPQQU (actually an LW parents post)
The cited article is this:
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