Is the following an experiment or an observational study?

to examine whether eating brown rice affects metabolism, we ask a random sample of people whether they eat brown rice and we also measure their metabolism rate.

It's observational study

Explanation:

In observational study, researchers gather the data by simply observing the subjects without necessarily controlling the subjects. Inn experiment study, researchers will control the subjects. They wll determine what the subjects can or cannot eat, what substance they should take , etc.

From the example above, the researchers only ask the people (subject) about what they eat and measure it based on the answer. They do not control what type of nutrition that the people are taking, they gather the data based on the subjects' natural behavior.