Question 1.19

1.19 Walnuts and cholesterol. Does eating walnuts increase the level of good cholesterol (HDL) and reduce the level of bad cholesterol (LDL)? Here are two ways to study this question.

  1. 1. Researchers in Australia recruited 58 adults with diabetes for a research study. These subjects were randomly assigned to two treatment groups: a low-modified-fat diet group and a low-modified-fat diet group that included a handful of walnuts each day. After six months, researchers compared changes in HDL and LDL levels for the two groups.

  2. 2. Another team of researchers recruited 58 adults with diabetes who regularly eat walnuts as part of their diet. The researchers match each with a similar adult with diabetes who does not regularly eat walnuts. The researchers measured the HDL and LDL for each adult and compared the results for both groups.

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  1. (a) Explain why the first is an experiment and the second is an observational study.

  2. (b) Why does the experiment give more useful information about whether walnuts increase HDL and reduce LDL?