PrepTest 126, Section 3, Question 22
In a study, one group of volunteers was(72 more words not shown)
Which one of the following,(7 more words not shown)
- AA low-protein, high-carbohydrate(30 more words not shown)
- BMany people who(12 more words not shown)
- CA high-protein, low-carbohydrate(21 more words not shown)
- DIn the experiment,(26 more words not shown)
- EMany of the(26 more words not shown)
Reading the argument
Best out of two doesn't mean best of all.
The study compares a high-protein, low-carbohydrate diet with a low-protein, high-carbohydrate diet. Holding calories equal addresses one possible difference, but I still have questions. Did the groups exercise equally? Were they comparable in other relevant ways? And after just ten days, we learn that one group lost more weight—not necessarily more body fat. Weight could also change through losing something other than fat, such as muscle.
Even if the study established that one of these diets was better, why call it the most effective way? There could be another diet that works better than both. The comparison hasn't examined every possibility.
What we’re looking for
For the weaken question, my first choice would be evidence of a better alternative. The exercise question and the shift from weight to fat give us other possible ways to challenge the inference. Let's see which one the answers develop.
Working the answers
- ACorrect
This takes the weight-versus-fat route. The high-carbohydrate group retains water that largely offsets the weight of fat it loses. Its smaller change on the scale may therefore hide meaningful fat loss. The low-carbohydrate group doesn't have that same offset.
So the diets' different weight results don't give us a clean comparison of fat loss. This isn't the better third diet I first predicted; it questions what the existing comparison measures. A doesn't prove the high-carbohydrate diet loses more fat. It gives a concrete reason that losing less total weight needn't mean losing less fat, which weakens the evidence for the claimed winner.
- B
Eating lots of protein isn't the whole recommended diet. These people might also eat lots of carbohydrates, while the recommendation combines high protein with low carbohydrates. B doesn't establish that they're following the proposed approach, much less compare its effectiveness under the study's conditions.
- C
Take the answer's described effect as a hypothetical for this question: body fat decreases even though overall weight doesn't significantly fall. That isn't evidence against the recommended diet's ability to reduce fat. Although it also distinguishes fat loss from scale weight, it describes a fat-reducing effect of the high-protein, low-carbohydrate approach rather than showing that the competing approach's fat loss was hidden.
- D
The exercise difference goes the wrong way for the objection. It is the high-carbohydrate group that exercises, yet the low-carbohydrate group loses more weight without it. That doesn't explain the low-carbohydrate group's advantage as the result of extra exercise. It still wouldn't prove the claim about the best way to lose fat, but it supplies no such weakener.
- E
Regaining weight after returning to the old diet doesn't establish how effective the tested diet was while people followed it. The conclusion concerns losing body fat, not a promise that its effects will persist after the diet stops. We also still lack a comparison of fat loss between the diets.
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