Recently, Soylent reported that a small number of consumers have reacted negatively to the Soylent Bar and Soylent Powder 1.6. Soylent has decided to remove algal flour from its formulations, but has released no data that shows algal flour is the cause of the adverse reactions. I have conducted a preliminary review of the ingredients list for "Soylent Powder 1.6" and "Soylent Bar.” Although no concentrations are provided for either formula, both represent a complex witch's brew of over 25 substances and at least one drug, Phytonadione (a prescription form of vitamin K). Some of the ingredients are identified specifically, but others are identified only by generic names, which does not distinguish the ingredient from other forms of the same substance (e.g., chromium chloride).
In regard to the complaint of "nausea and other stomach issues," there are a number of ingredients incorporated into the Soylent products that may cause this problem. For example, copper gluconate is known to cause stomach upset, zinc sulfate may result in acute stomach distress in high doses, and ferrous gluconate is known to be corrosive to the gastrointestinal tract and may cause diarrhea, nausea and vomiting of blood.
Substances more associated with lower tract issues (including, but not limited to diarrhea, cramping, gas and bloating) are often associated with the fermentation of carbohydrates and creating an osmotic diarrhea; this is typical of isomaltooligosaccharide which contains digestion resistant alpha-(1,6)-glycosidic linkages. Other ingredients potentially leading to discomfort include the soy protein isolate and modified food starch. Certain phosphate salts (such as certain species of magnesium phosphate and tricalcium phosphate) are used clinically to induce bowl evacuation prior to colonoscopy. There is at least one report of diarrhea from manganese sulfate. Magnesium oxide (in the bars only) is routinely used to relieve chronic constipation.
The Bloomberg news article points out the claim by Soylent, that because the new formulations of both the bar and drink powder (Soylent 1.6) contain the Whole Algal Flour, which had hitherto not be present, the algal flour must therefore be the causative agent. This conclusion is premature without additional investigation of the other possibilities recited above. While it is entirely possible that there may be some synergistic effects between ingredients resulting in an undesirable effect, I do not believe Whole Algal Flour or any single ingredient (at normal, sub-clinical use levels) can be identified as the causative agent; there is just no evidence to indicate a cause-effect relationship for a single ingredient in such a complex mixture.
A more likely scenario and especially in consideration of all the other ingredients with documented potential for gastrointestinal side effects, is that there may have been a formulation error in the new product and/or an increase in one ingredient or another that has tipped the balance in a negative manner to favor a combination of ingredients producing stomach upset.