Can you have malabsorption with weight loss?

Yes. Rapid weight loss (intentional or unintentional) due to any reason, including dieting and gastric-bypass surgery (bariatric surgery) of any kind may lead to mal-absorption syndrome. In particular for dietary vitamins and trace elements, as well as essential fatty acids. Thus, working closely with a healthcare professional who is aware of such is impotent in preventing nutritional abnormalities.