Q24

[logicfiend]

Q asks if someone is given drug that inhibits actions of serotonin, what would expected to happen?

What do we know?

Paragraph 3 tells us:
-Originally rats with both carb and protein rich foods, alternate between foods.
-After given drug to interrupt serotonin actions, rats would fail to respond to carbs intake, would keep eating.

Paragraph 4 tells us:
-drugs inhibiting serotonin can have various effects, depending on the drug.
-if drug blocks releases/blocks serotonin to selectively suppress carbs, can help someone successfully suppress cravings and avoid weight gain seen in other drugs.
-another drug that only blocks serotonin has opposite effect of encouraging carb craving, and leading to weight gain.

While presented in different ways, paragraphs 3 and 4 both agree that inhibiting serotonin actions without additional factors will generally increase one's cravings for carbs.

Now the answers:

A) Correct. Subjects would show preference for carbs vs. proteins—The only place proteins are mentioned are in paragraph 3. Here we need to connect a few points. That the rat when given drug to inhibit serotonin did not respond to carbs intake, kept eating. So you can assume when given the drug and given a choice between carbs vs. proteins, he would choose carbs more frequently because he cannot suppress the craving.

BUT, the passage doesn't give a comparison of protein intake during carb cravings. The saving grace of this answer choice is the word "probably" which lets us more comfortably make the leap that between the two, when he is craving carbs, he will PROBABLY choose carbs over proteins.

B) Sleep after carb rich meal—sleepiness, feeling refreshed after carb rich meal, these are all attributes of people that crave carbs. Not related directly to drug inhibiting S actions.

C) Subjects more likely to lose weight than before drug—upon reviewing, I choose this answer after crossing out A, but I hated myself for doing it. As I mentioned above, serotonin inhibiting drugs can have multiple consequences. All we know about this drug in Q is that it inhibits serotonin, we don't know if it functions like d-fenfluramine as mentioned in paragraph 4. We also don't know if it functions like the drugs mentioned in line 51. Therefore, we can't make an inference on the weight gain or loss that can be had here, because there are other factors that affect this.

D) blood tryptophan would increase—well, we now that T leads to S, so if S is inhibited (or decreases), doesn't make sense that T would increase. Or if we're pushing the chain backward, we don't know what affect decrease on S would have on T.

E) desire for both carbs and proteins would increase—The same issues I originally had with A. We don't know when serotonin is inhibited and carb cravings increased, what happens to cravings for protein. Passage does not make any comment on protein cravings or desire in conjunction with levels of serotonin.

Please correct anything that is wrong here!

[rinagoldfield]

Thanks for your post, logicfiend !

The effects of these drugs are confusing, so let’s make sure we have them straight:

Paragraph 3 tells us:

Drugs that enhance serotonin lower carb cravings in rats
Drugs that inhibit serotonin* induce carb cravings in rats

*they interrupt serotonin neurotransmission, meaning the serotonin doesn’t get properly released.

Paragraph 4 tells us:

Drugs that enhance serotonin* lower carb cravings in humans
Drugs that block serotonin induce carb cravings in humans

*this kind of drug “releases serotonin into brain synapses and then prolongs its [serotonin’s] action by blocking its reabsorption into the presynaptic neuron” (lines 46-48). In other words, these drugs make serotonin extra-strong

This can be boiled down to: serotonin and carb cravings are inversely related.

The question asks about the effects of a drug that inhibits serotonin; it can be inferred that carb cravings will go up.

(A) talks about carb-cravings going up, but protein? Hmm. Hold onto this one for now.

(B) is the opposite of what we’re looking for. This is the result of a drug that lowers carb cravings.

(C) is also the opposite of what we’re looking for. Subjects lose weight when their carb cravings go down, not up.

(D) is unsupported. We don’t know the relationship between serotonin-focused drugs and tryptophan.

(E) also talks about carb cravings going up, but again, what’s up with the protein?

Down to (A) and (E). We can choose (A) because of the rat experiment described in paragraph 3. That paragraph describes undrugged rats eating proportionally similar amounts of carbs and protein. After the rats were given serotonin-blocking drugs, they started eating more carbs. The author use this study to support the idea that carbs and serotonin are specially linked, so we can infer that they chose these carbs over protein.**

**If the rats were still favoring protein as much as carbs, the implications of the study would be different.

***Yeah, we’re looking for the most provable answer here.

Hope that helps!

[logicfiend]

Ah your breakdown makes this question a lot easier when you boil it down to the essentials (i.e. how serotonin or lack there of, impacts cravings).

Thanks so much for clarifying!

P.S. this forum is so incredibly helpful. Thanks for all your efforts!