I used to have the student fly a low level downwind turn In two ways. First fly it looking out at the ground- result invariably a loss of airspeed. Second fly the same turn looking only at the instruments- result no loss of airspeed. The problem in this scenario is the visual effect of the apparent gain in speed as you turn downwind. HOWEVER, I have observed that if it is a climbing turn onto the downwind, that is climbing with an increasing tailwind component, maintaining airspeed does need a more nose down attitude to maintain airspeed.