Leptin, a protein occurring naturally in the blood, appears to

Question

Which of the following most logically completes the passage?

Leptin, a protein occurring naturally in the blood, appears to regulate how much fat the body carries by speeding up the metabolism and decreasing the appetite when the body has too much fat. Mice that do not naturally produce leptin have more fat than other mice, but lose fat rapidly when they are given leptin injections. Unfortunately, however, leptin cannot be used as a dietary supplement to control fat, since __________.

(A) the digestive system breaks down proteins before they can enter the bloodstream
 
(B) there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism
 
(C) people with unusually low levels of leptin in their blood tend to have a high percentage of body fat
 
(D) the mice that do not naturally produce leptin were from a specially bred strain of mice
 
(E) mice whose bodies did produce leptin also lost some of their body fat when given leptin injections

NEW question from GMAT® Official Guide 2019 
(CR04159)

Step 1: Identify the Question

The argument contains a blank space, and the question asks which answer choice most logically completes the passage. Fill-in-the-blank questions are typically Strengthen questions; however, to be sure of what problem type this is, read it and determine the logical relationship between the blank and the rest of the passage.

Step 2: Deconstruct the Argument

L: regulates fat (met. ↑, app. ↓)

Mice w/ no L: fat ↑, BUT L injections → fat ↓

BUT: L not a dietary supp. for fat, b/c ??????

The first part of the argument describes the fat-regulating properties of leptin. It appears to reduce fat when injected into mice. But, there’s a catch: surprisingly, it can’t be used as a dietary supplement. The argument doesn’t explain why this is; instead, that section is left blank. Because you’re asked to explain a surprising fact with no prior evidence, treat this as an  Explain the Discrepancy  problem.

Step 3: Pause and State the Goal

On Explain the Discrepancy problems, the right answer will give a reason for the surprising phenomenon to have occurred. In this case, the right answer needs to give a valid reason that leptin can’t be used as a dietary supplement.

Step 4: Work from Wrong to Right

(A) CORRECT . This explains why leptin can’t be used as a dietary supplement: if it’s eaten, it is broken down by the digestive system and can’t enter the bloodstream. Therefore, it would be ineffective. This is consistent with the statements in the argument: leptin naturally occurs in the blood, and is effective when injected.

(B) The surprise in this argument is specifically that leptin is ineffective. Whether other pharmaceuticals have similar effects doesn’t bear on whether leptin itself is effective.

(C) If anything, this suggests that leptin is a useful supplement, which is the opposite of what the right answer should do. However, it also doesn’t directly relate to the argument, since it doesn’t clarify whether leptin is an effective supplement—it only describes naturally occurring leptin.

(D) The mice in the experiment were injected with leptin, not given leptin as a dietary supplement. Therefore, information about the mice doesn’t help determine whether leptin is effective as a dietary supplement.

(E) The mice in the experiment were injected with leptin, not given leptin as a dietary supplement. Therefore, information about the mice doesn’t help determine whether leptin is effective as a dietary supplement. Additionally, this suggests, if anything, that leptin is effective, which is the opposite of what the right answer should do.

D3N0 · Accepted Answer

Ans: A {IMO}
As per the stem Leptin can not be used as a dietary supp to control fat. means so we need a reason for the same to complete the passage that why Laptin can not be used as Dietary Supp.

State A clearly says that because digestive system breaks down the proteins before entering the blood stream and from stem we know Leptin (a type of protein) occurs in blood, so if Leptin is not reaching the blood stream feeding it won't make any difference and it won't serve its purpose.

A. the digestive system breaks down proteins before they can enter the bloodstream (Correct)
B. there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism (Not Relavent)
C. people with unusually low levels of leptin in their blood tend to have a high percentage of body fat (Not rel)
D. the mice that do not naturally produce leptin were from a specially bred strain of mice (Not Rel)
E. mice whose bodies did produce leptin also lost some of their body fat when given leptin injections (this speaks about injection not as food supp so not rel)

GyMrAT · Answer

Question Type: Complete the Argument/Weaken

Analysis: Leptin, a naturally occuring protein, regulates accumulation of body fat by controlling hunger & metabolism. This is supported by the research on mice that do not naturally produce leptin & are injected with supplemental leptin, have shown to lose fat. The leptin in the blood stream of mice is able to carry out its function of reducing fat.

Since the conclusion starts with "Unfortunately..." we need to find a statement that will weaken, the claim of usage of leptin as a dietary supplement to lose fat.

A. the digestive system breaks down proteins before they can enter the bloodstream -  Correct. Since if leptin is broken down by the digestive system, before it reaches the blood stream, it may not be able to carry out its intended function of regulating fat loss.  
 
B. there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism - Incorrect. Out of scope.
 
C. people with unusually low levels of leptin in their blood tend to have a high percentage of body fat - Incorrect. Restates an outcome of the premise of the argument.
 
D. the mice that do not naturally produce leptin were from a specially bred strain of mice - Incorrect. If the mice were from a special bred, we do not know whether they are resistant to leptin & had some other mechanism for loosing fat.
 
E. mice whose bodies did produce leptin also lost some of their body fat when given leptin injections - Incorrect. Supports the usage of leptin, since maybe they produced low levels of leptin & supplemental leptin helped them reduce their body fat.

Answer A.

Thanks,
GyM

ENEM · Answer

time taken 2:58

I got the answer via POE

We need to show why leptin can't be used as a dietary supplement...

B. there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism
 out of scope, even if there are other pharmaceuticals, that doesn't answer why leptin can't be used as a dietary supplement.

C. people with unusually low levels of leptin in their blood tend to have a high percentage of body fat
 out of scope, even if they do have high percentage of body fat, this doesn't tell us why leptin won't help reduce that fat.. .

D. the mice that do not naturally produce leptin were from a specially bred strain of mice
 so what? out of scope

E. mice whose bodies did produce leptin also lost some of their body fat when given leptin injections
 this tells us a case in which leptin has helped in reducing body fat, doesn't address the issue at hand.

hence via POE answer is  A

strange but I feel I've seen this question before :/

aragonn · Answer

pre-think - We need to tell why leptin can't be used as dietary substance. Well we know that when injected direct in blood it is working as intended but taking is as diet its not working. it means something in b/w in working on it. in this case A is explaining in perfect way. A must be the answer.

A. the digestive system breaks down proteins before they can enter the bloodstream

A. the digestive system breaks down proteins before they can enter the bloodstream

jayarora · Answer

Argument: Leptin, a protein found in blood, appears to regulate fat. But leptin cannot be used as a dietary supplement to control fat because __________

We are looking for a choice that shows despite consuming leptin, it will not regulate fat. Option A states that digestive system will break it down. Thus it's the answer we are looking for.

Skywalker18 · Answer

Leptin, a protein occurring naturally in the blood, appears to regulate how much fat the body carries by speeding up the metabolism and decreasing the appetite when the body has too much fat. Mice that do not naturally produce leptin have more fat than other mice, but lose fat rapidly when they are given leptin injections. Unfortunately, however, leptin cannot be used as a dietary supplement to control fat, since __________.

A. the digestive system breaks down proteins before they can enter the bloodstream - Correct -- so injection works but eating won't
 
B. there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism -- Irrelevant
 
C. people with unusually low levels of leptin in their blood tend to have a high percentage of body fat -- Incorrect - this does not explain why leptin CANNOT be used as a dietary supplement to control fat
 
D. the mice that do not naturally produce leptin were from a specially bred strain of mice -- Irrelevant
 
E. mice whose bodies did produce leptin also lost some of their body fat when given leptin injections -- Incorrect -- this says that Leptin is effective to a certain extent even when one produces it

Answer A

Businessconquerer · Answer

Ok look guys, I know that the option A will take a lot of time to process and understand that leptin occurs in blood and since break down happens before that protein doesn't reach blood.

That is ok if you got it,

if you don't understand that, skip the option and look at B,C,D,E
It is easier to understand and eliminate them

REMEMBER
On GMAT if one option is wayyyy to technical to understand, try to eliminate the others, this way, you get to be the boss, and avoid the unnecessary waste of time.\

If you find two option that you do not understand, either skip the question or, if you can, take about a minute more and solve it

emcheeks · Answer

I agree with what  Businessconquerer  said. If you can't get you logic straight when working on technical answer choices like A, simply skip it and see if POE can help you.

Here is my 2 cents for choosing A anyways:

If digestive system breaks down protein, so it does to Leptin (also a protein). Therefore, Leptin can never reach bloodstream, and doesn't have any effects. Why? From the passage, we know that mice are given leptin injections, and we know injections work by going into the bloodstream.

CEdward · Answer

Which of the following most logically completes the passage?

Leptin, a protein occurring naturally in the blood, appears to regulate how much fat the body carries by speeding up the metabolism and decreasing the appetite when the body has too much fat. Mice that do not naturally produce leptin have more fat than other mice, but lose fat rapidly when they are given leptin injections. Unfortunately, however, leptin cannot be used as a dietary supplement to control fat, since __________.

(A) the digestive system breaks down proteins before they can enter the bloodstream 
Correct. However, note that this choice does have a flaw. The assumption being made here is that leptin, a protein naturally occurring in the blood, must also function in the blood. Is it likely the case? Yes…but we don’t actually have further information to tell us about the complex signalling pathways …maybe there are other alternative pathways that leptin can exert its effects.

(B) there are pharmaceuticals already available that can contribute to weight loss by speeding up the metabolism X
-Does not explain why leptin cannot be used as a supplement

(C) people with unusually low levels of leptin in their blood tend to have a high percentage of body fat X
-This just gives us a little more detail about what is already known in the passsage

(D) the mice that do not naturally produce leptin were from a specially bred strain of mice X
-besides the point

(E) mice whose bodies did produce leptin also lost some of their body fat when given leptin injections X
-Validates the function of leptin, but sidesteps the issue of leptin as a supplement

mSKR · Answer

Leptin in dietary supplement goes in stomach but digestive system break down all proteins in stomach , it means leptin is also broken down. It means it can't reach to blood stream. Thus it can't have any effect. 
It strengthens the conclusion.

kaomanfen · Answer

I'm super confused now, if "the digestive system breaks down proteins before they can enter the bloodstream", how did it work on the injection for mice ?

mSKR · Answer

protein works when given as injection beccause it enters directly in the blood stream( injection is inserted in blood streams) . --> so far so good
but it doesnt work as DIETARTY SUPPLEMENT because
you eat---> digestive system ---> then was supposed to go in blood stream to function properly 
A says: it can not reach to blood stream ,
So this protein is useless if directly eaten.

I hope it helps .

VerbalBot · Answer

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Leptin, a protein occurring naturally in the blood, appears to

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