In cases 1-3, the data are judged inconsistent with a population mean difference of 0. In cases 4-6, the data are consistent with a population mean difference of 0. There is a difference between the diets, but it is of no practical importance. The difference may or may not be of practical importance. The interval is too wide to say for sure.
More study is needed.
We are confident that if there is a real difference it is of no practical importance. We cannot claim to have demonstrated a difference. The population mean difference is not well enough determined to rule out all cases of practical importance. Cases 5 and 6 require careful handling. While neither interval formally demonstrates a difference between diets, case 6 is certainly more suggestive of something than Case 5.