Я редко ем сгущёнку, потому что она слишком сладкая для меня.

Because сгущёнка is the direct object of ем (I eat), so it goes into the accusative case.

• Dictionary form: сгущёнка
• Accusative singular: сгущёнку

This is a very common pattern for feminine nouns ending in -а:

• книга → книгу
• машина → машину
• сгущёнка → сгущёнку

So Я ем сгущёнку literally follows the pattern I eat + object.

Есть is the infinitive, meaning to eat.
In the sentence, you need the 1st person singular form: I eat, which is ем.

This verb is irregular:

• я ем — I eat
• ты ешь — you eat
• он/она ест — he/she eats
• мы едим — we eat
• вы едите — you eat
• они едят — they eat

So Я редко ем... means I rarely eat...

Because the sentence describes a habit or general tendency: I rarely eat condensed milk.

In Russian, habitual or repeated actions usually use the imperfective:

• ем = I eat / I am in the habit of eating

A perfective form like съем would mean something more like I will eat up or I will consume completely once, which does not fit the idea of rarely as a general habit.

So:

• Я редко ем сгущёнку = general behavior
• Я съем сгущёнку = I will eat the condensed milk up

Редко is an adverb meaning rarely, and in Russian adverbs often come before the verb they modify.

So:

• Я редко ем сгущёнку = the most neutral word order

Russian word order is flexible, so other orders are possible, but they may change emphasis:

• Я ем сгущёнку редко — puts a little more focus on rarely
• Сгущёнку я редко ем — emphasizes condensed milk

The original sentence is the most natural neutral version.

Yes, you often can.

Russian frequently omits subject pronouns when the verb form already makes the subject clear. Since ем clearly means I eat, Редко ем сгущёнку is perfectly natural.

However, keeping я is also natural. It can make the sentence sound slightly fuller or more explicit.

So both work:

• Я редко ем сгущёнку
• Редко ем сгущёнку

Because она refers back to сгущёнка, and сгущёнка is a feminine noun.

In Russian, pronouns agree with the noun’s grammatical gender:

• masculine noun → он
• feminine noun → она
• neuter noun → оно

So:

• сгущёнка is feminine
• therefore: она слишком сладкая

Even though in English it is used for things, Russian uses he/she/it according to grammatical gender.

Because the adjective must agree with the noun or pronoun it describes.

Here, сладкая describes она, which refers to сгущёнка, a feminine noun. So the adjective must also be feminine singular:

• masculine: сладкий
• feminine: сладкая
• neuter: сладкое
• plural: сладкие

So:

• она сладкая — she/it is sweet
• сгущёнка сладкая — condensed milk is sweet

Because сладкая is an adjective, while сладко is usually an adverb or a predicative form.

In this sentence, Russian is literally saying:

• it is too sweet for me

So it needs an adjective agreeing with она:

• она слишком сладкая

You would use сладко in different structures, for example:

• Здесь сладко пахнет — It smells sweet here.
• Мне слишком сладко — It’s too sweet for me.
  This is possible, but it is a different structure.

In your sentence, сладкая is the natural choice because it describes the noun directly.

Literally, для меня means for me.

In this sentence, it means for my taste, from my point of view, or for me personally:

• она слишком сладкая для меня
  = it is too sweet for me

This makes the statement more personal and subjective. Without для меня, the sentence would sound more absolute:

• она слишком сладкая — it is too sweet

With для меня, it becomes:

• она слишком сладкая для меня — it is too sweet for me personally

Because потому что introduces a subordinate clause: because it is too sweet for me.

Russian normally puts a comma before subordinate clauses, so:

• Я редко ем сгущёнку, потому что она слишком сладкая для меня.

This is very standard punctuation.

Also, потому что functions together as the conjunction because. Normally you do not split it internally with another comma in a simple sentence like this.

Yes, it is one of the most common and neutral ways to say because in everyday Russian.

Other options exist, for example:

• так как — since / because
• из-за того что — because of the fact that
• ведь — after all / because, but with a different tone

For a straightforward sentence like this, потому что is the most natural choice.

Сгущёнка is the common everyday word for sweetened condensed milk.

The fuller, more formal expression is:

• сгущённое молоко — condensed milk

In everyday speech, Russians very often say simply:

• сгущёнка

So the sentence sounds natural and colloquial.

Also note:

• сгущёнка is a noun
• сгущённое молоко is a noun phrase with an adjective + noun

The letter ё is important because it shows both the pronunciation and the stress.

• сгущёнку is pronounced roughly like sgoosh-CHYON-koo
• the stress falls on -щён-

A key point: ё is always stressed.

Many Russian texts replace ё with е, especially in casual writing, so you might sometimes see сгущенку. But the correct pronunciation is still with ё.

For learners, it is very helpful when ё is written, because it removes ambiguity.

Not if you want the same meaning.

• очень сладкая = very sweet
• слишком сладкая = too sweet

In the original sentence, the speaker is explaining why they rarely eat it, so too sweet fits much better:

• потому что она слишком сладкая для меня

If you say очень сладкая, it only states a strong degree of sweetness, but it does not necessarily imply that this is a problem.