I've read that because of the higher temperature specially vegetables lose more nutrients in a pressure cooker as opposed to a normal cooking method. Is this true?
According to Eating Well who consulted a food scientist, yes, some heat sensitive nutrients are lost, but no more so than other forms of cooking:
Pressure cooking can reduce heat-sensitive nutrients (e.g., vitamin C, folate) and bioactive phytonutrients, such as betacarotene, glucosinolates (helpful compounds found in cruciferous vegetables) and omega-3 fatty acids, that are beneficial for human health. But so do other cooking methods—and generally to more or less the same extent.
but in other cases, as in grains and legumes, the pressure-cooking is helpful:
in the case of grains and legumes, although the vitamins and heat-sensitive vitamins and phytonutrients are vulnerable to deterioration, the net result of pressure-cooking is a positive nutritional gain—from the increased digestibility of the macronutrients (protein, fiber and starch) and the increased bioavailability of the essential minerals.