The fact is that nutritional depletion following bariatric surgery can lead to protein wasting, loss of iron, depletion of biotin, B12, Vitamin A, Vitamin D, calcium, zinc, magnesium, fatty acids, and sufficient calories each day. This can lead to stress on the hair shaft. Very few structures metabolize as rapidly as hair. This means that hair needs more nutrition daily than other body structures. When protein is lost in sufficient quantities along with vitamins and minerals, hair shafts cease to elongate, go into the resting phase, and shed. All the factors lead to hair loss. The question is whether this hair loss is permanent. This has not been properly addressed over time, but it needs to be evaluated.
Bariatric (Weight Loss) Surgery: Metabolic, nutritional, psychological and physiological Consequences
You will often see sources that recommend protein, biotin, silica, and snake oil shampoos such as Nioxin to promote hair growth following bariatric surgery. Many of these sources are just trying to sell your products because you have hair loss and it bothers you. They often suggest a single product and offer to sell it to you. Perhaps dietary manipulation will help to retard hair loss, but it may be that you must reverse the bariatric surgery to overcome the associated hair loss from long-term nutritional depletion.