Dietitian: Eating fish can lower one' s cholesterol level  In a study of cholesterol levels and diet, two groups were studied  The first group ate a balanced diet including two servings of fish per week  The second group ate a very similar diet, but ate no fish  The first group showed lower cholesterol levels, on average, than the second group
The two groups had displayed similar average cholesterol levels prior to the study
It rules out an alternative explanation of the data collected in the study.