What is the structure of "For each item of food you eat, you have to weigh it and then find out the number of calories"?

Question

A passage from the book "Fitbit For Dummies" by Paul McFedries:

The main excuse people use to not track the food they eat is that it's just too hard. For each item of food you eat, you have to weigh it and then find out the number of calories. And if you want to track macronutrients such as carbohydrates, fat, and protein, the task is even harder.

I don't understand with what grammar structure the following sentence is made:

(1) For each item of food you eat, you have to weigh it and then find out the number of calories.

I can only understand the usual word order as in my variant:

(2) You have to weigh each item of food you eat, and then find out the number of calories.

Could somebody explain to me the logic of writing (1)? Because I also want to be able to make up the sentences having the structure analogous to (1).

Answer 1

It's a kind of topicalization. None of the examples in that article introduce the topic with "for", (apart from one where the phrase started with "for" in its original position), but it's a natural way to introduce a topic starting with each.

Answer 2

It is simply another way to state the sentence. English allows speakers a wide variety of ways to say something, which are a matter of personal style.

Consider:

Every time I go to the park, I eat a cake.

I eat a cake every time I go to the park.

Either alternative is good. The meaning is identical. Which one a writer uses is down to their preference.

As @Kate Bunting mentioned in a comment, the order chosen by the author in your example might be argued to place a little extra emphasis on "each item of food".

The complexity for an English learner probably arises from the need to use "for each" in your example.

Reversing the order of the clauses in this instance requires the addition of "for" before each. The many uses of "for" in English are difficult to grasp, but one of its purposes is as a function word in cases of enumeration or selection. Eg.:

For every action there is an equal and opposite reaction.

Furthermore the author has slightly over-complicated the sentence with the following construction:

For each item of food you eat, you have to weigh it ...

It's marginal, but the phrase is a little cludgy, although far from ungrammatical. However, it makes it harder to understand why and how "for" is being used.

These two sentences below straighten out the syntax a bit to show you how the clauses can be reversed in normal circumstances.

A calculation of weight has to be carried out for each item of food.

For each item of food, a calculation of weight has to be carried out.

Answer 3

I'll try to answer my own question.

(1) For each item of food you eat, you have to weigh it and then find out the number of calories.

It seems to me I have found that technical way which (1) went through to become itself.

The initial sentence was:

(1a) You have to find out the number of calories for each item of food you eat.

Move “for each item of food you eat” to the beginning:

(1b) For each item of food you eat, you have to find out the number of calories.

Add “weigh it and then”:

(1) For each item of food you eat, you have to weigh it and then find out the number of calories.

And it’s interesting when “weigh” appears “it” must also appear because perhaps if there were not the "it" then "to weigh" would be perceived as "to weigh + for each item of food you eat" (which is incorrect) but not as "to weigh + each item of food you eat" (which is correct).