Dietary researcher: A recent study reports that laboratory animals tha

IMO A.

Basically A simply illustrates the explanation provided in last two sentences of the question: reduction in calorie doesn't prolong life-span, but restate the normal life-span because humans over-eat.

Also by elimination B C D E can't be right either.

ok B weakens the author's conclusion ....we need to weaken the researcher's conclusion so it is actually a strengthen question not weaken question


My answer: A

can someone please explain this in detail? The premise has been so badly written that it very difficult to understand what is the dietary researchers conclusion and what is the authirs conclusion.

Dietary researcher:

Premise:
1. A recent study reports that laboratory animals that were fed reduced-calorie diets lived longer than laboratory animals whose caloric intake was not reduced.

Conclusion:
1. Some doctors advocate reduced-calorie diets, in the belief that North Americans’ life spans can thereby be extended.


Author:

Premise:
1. Laboratory animals tend to eat much more than animals in their natural habitats, which leads to their having a shorter life expectancy.

2. Restricting their diets merely brings their caloric intake back to natural optimal levels and reinstates their normal life spans.

Conclusion:
1. Doctors' conclusion is not supported.

I'm so enjoying to do GMAT , LSAT CR . They are so freaken cool

In this sentence , it is clearly that A is the winner .

Reseacher found that when you are old enough to have sex , sex is good for you and for your partner . But it is not applicable for you .

Reseacher assume that you are not old enough to have sex --> to weaken it you need to say that you are old enough to have sex .

This is an analogous comparing with this sentence . Research claim that this only work because the subject eat more than its normal diet --> to weaken it, we can say that Northern American consume larger that the norm does

GMATNinja, Could you please explain this it to me why A not C?

Dietary researcher: A recent study reports that laboratory animals that were fed reduced-calorie diets lived longer than laboratory animals whose caloric intake was not reduced. In response, some doctors are advocating reduced-calorie diets, in the belief that North Americans’ life spans can thereby be extended. However, this conclusion is not supported. Laboratory animals tend to eat much more than animals in their natural habitats, which leads to their having a shorter life expectancy. Restricting their diets merely brings their caloric intake back to natural optimal levels and reinstates their normal life spans.

Which one of the following, if true, would most weaken the dietary researcher’s argument?

(A) North Americans, on average, consume a higher number of calories than the optimal number of calories for a human diet. - CORRECT. POE helps. Not good to choose but anyway. This is not best since nothing about life expectancy is mentioned or inferable.
(B) North Americans with high-fat, low-calorie diets generally have a shorter life expectancy than North Americans with low-fat, low-calorie diets. - WRONG. Already low calorie diet. Fat is not a factor here. Importantly the comparison is not helpful.
(C) Not all scientific results that have important implications for human health are based on studies of laboratory animals. - WRONG. 2nd best for me. Which ones are or which ones not? Nothing specific about the study in the passage.
(D) Some North Americans who follow reduced-calorie diets are long-lived. - WRONG. Exceptions which is not helpful to make a generic statement or support it.
(E) There is a strong correlation between diet and longevity in some species of animals. - WRONG. Is it positive one or a negative one? we don't know so eliminate.

Answer A.

­First, let's review the argument:

• In the lab, we had two groups of mice: Group A was fed reduced-calorie diets while Group B's caloric intake was not reduced. Group A lived longer, and some doctors concluded that reducing calories in human diets could increase human lifespans.
  
• But the dietary researcher disagrees: the researcher notes that Group A's "reduced" diet actually represented a natural/optimal diet for animals in their natural habitats and that Group A's "increased" life spans were actually just "normal" life spans.
  
• In other words, the researcher is pointing out that the study did NOT involve (1) mice eating a natural/optimal diet and (2) mice eating LESS than natural/optimal. Instead, it involved (1) mice eating a natural/optimal diet and (2) mice eating MORE than natural/optimal. So even though the study does suggest that eating MORE than natural/optimal is bad, it does NOT suggest that eating LESS than natural/optimal is good.
  
• So if humans are already eating a natural/optimal amount, there's no evidence that eating any less will increase their lifespans. Who knows, maybe it will actually be bad..?

There's an implied assumption in the logic, which is that humans are generally eating natural/optimal levels of food. If that is indeed the case, then the researcher is right: the study only tells us about natural/optimal vs. MORE than natural/optimal, so we shouldn't use it to draw conclusions about natural/optimal vs LESS than natural/optimal.

But what if humans are generally eating way more than natural/optimal levels of food? In that case, the study IS in fact relevant, and the doctors are justified in suggesting that we all reduce our caloric intake, to go from "above natural/optimal" down to "natural/optimal". 

So (A) would support the doctors' advice and thus weaken the dietary researcher's argument.

As for (C): if this is true, then SOME scientific results that have important implications for human health are NOT based on studies of laboratory animals. Well, who cares? All sorts of other studies -- studies of plants, studies of humans themselves, studies of computer models, and so on -- could have important implications for human health. That doesn't mean that studies of laboratory animals are (or are not) useful, so this has no bearing on the dietary researcher's argument, or on the doctors' conclusion. 

(A) is our winner.­­­