Energy Drinks: Popular energy drinks contain green tea extract and caffeine. Do these energy drinks help you lose weight by increasing your metabolism?
Researchers at a medical school designed an experiment to determine the chemical effects of green
tea and caffeine on energy metabolism in healthy, lean, young adults.
Researchers randomly assigned participants to 2 treatments. One group drank Formula A, a beverage
with green tea and caffeine. The other group drank Formula B, a beverage with none of these
ingredients but colored to look like Formula A. The beverages were blinded at the production site, so
the experiment was double-blind.
The researchers chilled the beverages to 6°C. Participants drank the beverages at the same time
each day for three days. During the 3 days of the experiment, the researchers fed each participant
the same diet. On the 3rd day participants spent 24 hours in a calorimeter chamber to measure their
energy metabolism. The medical journal Obesity published the results in 2007.
Which confounding variable is controlled by randomly assigning individuals to treatments?
the physical fitness level of the participants
the effect of green tea and caffeine on energy metabolism
the time of day participants drank the beverages