Remember the AD7730 is a very sensitive device - I got caught out when I first used it. If you short the + & - inputs the output value should be close to zero otherwise you will get what is random values. Even when you connect a load cell, the lower bits will be random due to noise - ignore the lower bits. I ended up using a ADUC834 as it is about the same price as just the AD7730. In my application I ignore the lower 8 bits as they are just noise.