#6: Dietitian: High consumption of sodium increases some

[Administrator]

Complete Question Explanation

Assumption. The correct answer choice is (E)

The stimulus contains the following structure:

• Premise: Sodium increases the risk of heart disease.
  
  Premise: The potassium in plant foods helps reduce that risk.
  
  Conclusion: Eat fresh, rather than canned or frozen, fruit and vegetables.

The author recommends eating fresh, rather than canned fruit and vegetables because the potassium
in plant foods counteracts the malign effects of sodium on your heart. It is entirely unclear why
eating fresh foods would be any better than eating canned or frozen ones. Because this is an
assumption question, the answer you select must contain a statement upon which the argument
depends, i.e. a statement that is necessary for the conclusion to be true. Typically, if you see a new
or “rogue” element in the conclusion, look for a Supporter assumption answer that links the new
element back to the premises. Since the distinction between fresh and canned plant foods did not
appear anywhere else in the argument, the Supporter assumption must state that fresh fruit and
vegetables contain more potassium than canned or frozen ones.

This prephrase reveals answer choice (E) to be correct.

Answer choice (A): This answer choice contains the wrong comparison: the higher proportion of
potassium to sodium in fresh fruit and vegetables does not mean that eating such foods will provide
us with a greater amount of potassium than canned or frozen ones. This comparison has no bearing
on whether we are better off eating one type of food over another.

Answer choice (B): This answer choice may seem attractive because it lends further credibility to
the recommendation that eating fresh fruit and vegetables is better than eating canned or frozen
ones. Indeed, if manufacturers often add sodium to canned or frozen foods, and sodium consumption
increases the risk of developing heart disease, it becomes even more likely that eating such foods is
bad for us. However, just because a statement supports the author’s conclusion does not mean it is
necessary for the conclusion to be true. Apply the Assumption Negation Technique and ask yourself,
“What would the author say to this negation?”

• Food processing businesses rarely add sodium to foods being canned or
  frozen.

The logical opposite of answer choice (B) implies that canned or frozen foods would have a
comparable amount of sodium to fresh fruit and vegetables, because no sodium would be added
during the manufacturing process. Nevertheless, it is still possible that fresh foods contain more
potassium than do canned or frozen ones. Since the potassium in plant foods helps to counteract the
effects of sodium, it is still possible that eating fresh fruit and vegetables is better for us.

Because the logical opposite of answer choice (B) does not weaken the conclusion of the argument,
answer choice (B) does not contain an assumption upon which the argument depends.

Answer choice (C): Whether potassium is the only mineral that helps to prevent sodium’s malign
effects has no bearing on the conclusion of the argument.

Savvy test takers would eliminate answer choice (C) immediately, because it does not make any
mention of the rogue element in the conclusion (“fresh fruit and vegetables”). Given that Supporters
connect new elements, one would suspect that the correct answer would include this element.

Answer choice (D): This is another attractive answer choice, because it supports the central premise
that potassium in plant foods protects against heart disease. As with answer choice (B), however, this
statement is not necessary for the conclusion to be true. Even if potassium in fruit and vegetables
did have some negative side effects, it is still possible that in moderate amounts it helps to prevent
sodium’s malign effects, or that the benefits outweigh the costs. Because the logical opposite of
answer choice (D) does not weaken the conclusion of the argument, this answer choice does not
contain an assumption upon which the argument depends.

Answer choice (E): This is the correct answer choice. Try the Assumption Negation Technique—
if fresh fruit and vegetables do not contain any more potassium than canned or frozen ones, the
author’s recommendation would make no sense.

[AlyssaY]

Answer choice (E): This is the correct answer choice. Try the Assumption Negation Technique—
if fresh fruit and vegetables do not contain any more potassium than canned or frozen ones, the
author’s recommendation would make no sense.

For this question, I understand why E is definitely the best answer choice available but I don't see how it is a necessary assumption of the argument. The stimulus does not talk about the AMOUNT of potassium, just that the PRESENCE of potassium (which we know from the stimulus is in all plant food) helps to prevent the negative effects of sodium. There's no reference that more potassium = greater prevention of negative effects of sodium. So negating answer choice E, which gives "fresh does NOT contain MORE potassium than canned/frozen", doesn't really weaken the author's conclusion. What if you only need 0.5units of Potassium to prevent negative effects of Sodium and fresh foods have 5 units and frozen foods have 3 units?

I was initially looking for an answer that said something about the canning/freezing process removing all potassium from plant foods, which would validate the author's conclusion about eating fresh rather than frozen, since only the fresh has any potassium to prevent sodium's negative effects.

Can someone please explain how E is necessary for the argument? Thank you!!!

[James Finch]

Hi Alyssa,

This is a Supporter Assumption, meaning that it introduces a new element in the conclusion that isn't in the premises. This means we need to treat it similarly to a Justify question, in that we can Prephrase joining the premises to the conclusion, although not usually in such a way that the conclusion will become a valid inference. However, if this Prephrase isn't true, then the conclusion will not be true either, so we can use the Assumption Negation technique to test any contending answer choices.

Here the new element is fresh fruits/vegetables being better at offsetting cardiac damage due to high-sodium diets than canned/frozen fruits/vegetables. We're told in the premises that the potassium in *plant foods* (a broad group that would contains both canned/frozen and fresh) helps to prevent damage done by sodium. But none of this helps in telling us why fresh would help more than canned plant foods. So the only logical Prephrase would be "fresh fruits and vegetables have more potassium than canned/frozen," as that's the only element present in the argument that could help make fresh better than canned or frozen fruits and vegetables. It doesn't actually make the conclusion inferentially valid, since there could still be a whole-to-part issue about, for example, how much potassium a fresh apple contains versus a frozen banana, but without it the conclusion doesn't follow because we wouldn't have any basis for the comparison.

It looks like you're bringing in an extra assumption about potassium levels being a set threshold above which more of it has no effect. Since we don't know this, we can't actually make this assumption. Additionally, it sounds like you were looking for a Sufficient Assumption, which would be the correct answer to a Justify question. But Necessary Assumptions are almost never Sufficient as well, so don't expect them to prove the conclusion true the way that your Prephrase would have done. Instead, they only enable the conclusion to be true, they don't prove it by themselves.

(E) is exactly this Prephrase, and when negated (Fresh fruits/vegetables do not contain more potassium than canned/frozen ones) the conclusion would also necessarily be negated (People with high sodium diets don't have any reason to eat fresh fruits/vegetables instead of canned/frozen ones).

Hope this clears things up!

[AlyssaY]

But Necessary Assumptions are almost never Sufficient as well, so don't expect them to prove the conclusion true the way that your Prephrase would have done. Instead, they only enable the conclusion to be true, they don't prove it by themselves.

Hi James,

THANK YOU so much for that explanation - I see now that I was looking for a statement that would prove the conclusion of the argument, not one that enabled it to be logically valid. So basically, the assumption necessary to the author's argument is one that describes why fresh should be selected over frozen. If we did not have that assumption, the author's argument would not follow. It's not necessary that frozen food is bad, just that there is a reason fresh is better than frozen in some way related to their potassium levels since that is the only support given for the author's conclusion.

Thanks again!