I am giving the answer just by thinking mathematically. It may lead you to a better and fruitful answer.You might have already thought of this.
For a gray image, when we set the lower-order bits to zero, the gray values of many of the pixels will decrease slightly. For example, the binary equivalent of 162 is 10100010. If we set the last 4 bit planes to zero, the number will become 160. However, the values of those pixels will not change which have already zeros at the respective positions. The frequencies of 128, 128+64, 128+64+32, etc. will increase. The histogram may slightly shift to the left.
For a color image, this may change the shades of the color or color itself.
As already stated, setting the LBS to 0 will eliminate every 2nd member (the odd ones) of the histogram. At the same time, the remaining members will show the sum of the previous even value (N) PLUS the value of its previous successor (N+1).
Be honest: are we solving your homework questions ?