Learn Hardcore Russian: Хотя я не на диете, я тоже стараюсь есть меньше калорий вечером. - Although I am not on a diet, I also try to eat fewer calories in the evening.

диета is a noun, feminine, nominative singular.
After the preposition на in the meaning "on / at (a state or regimen)," Russian uses the prepositional case: на диете.
- на работе – at work
- на пенсии – retired (on a pension)
- на диете – on a diet

You cannot say я не диета because that would literally mean "I am not a diet" (no preposition, wrong meaning).

You also can’t say на диета because на requires the noun to change case: диета → диете in the prepositional.

So the correct form for "I’m not on a diet" is я не на диете.

What exactly does Хотя mean here, and could the clauses be reversed?

Хотя means "although / though" and introduces a concessive clause: something that is true despite another fact.

Хотя я не на диете, я тоже стараюсь…
= Although I’m not on a diet, I still/also try…

You can reverse the order:

Я тоже стараюсь есть меньше калорий вечером, хотя я не на диете.

Both orders are correct. The meaning is the same; the difference is just which part you emphasize first. The comma is required to separate the Хотя-clause from the main clause.

What is the difference between тоже and также, and why is тоже used here?

Both can translate as "also / too", but they’re used a bit differently:

тоже: “too/as well,” usually about similarity to another person or situation; very common and neutral in spoken language.
- Я тоже стараюсь… – I also (me too) try…
также: more formal, often means “also/in addition,” joining items or facts in a more bookish or written style.
- Он читает книги, а также смотрит документальные фильмы.

In this sentence, the idea is "I, too, do this (like someone else)," so тоже is the natural, conversational choice:
…я тоже стараюсь есть меньше калорий вечером.

Why is it стараюсь есть, not стараюсь ем?

In Russian, стараться ("to try/strive") is followed by an infinitive, not a finite verb.

Pattern:

стараюсь + infinitive = I try to do X

So you say:

Я стараюсь есть меньше калорий. – I try to eat fewer calories.
Not:
✗ я стараюсь ем меньше калорий

Compare:

Я хочу есть. – I want to eat.
Я люблю есть сладкое. – I like to eat sweets.

In all these, the verb after хочу / люблю / стараюсь is in the infinitive: есть.

What does стараюсь add compared to пытаюсь? Both are "try," right?

Both mean "to try," but they have different nuances:

стараюсь (from стараться) – to make an effort, to strive; often about ongoing effort and good intentions.
- Я стараюсь есть меньше калорий. – I make an effort to eat fewer calories.
пытаюсь (from пытаться) – to attempt, to make an attempt; more neutral, sometimes closer to "I attempt (but might fail)."
- Я пытаюсь открыть дверь. – I’m trying (attempting) to open the door.

In the context of habits and self-control (food, exercise, study), стараюсь is more natural, because it emphasizes consistent effort rather than just attempts.

Is есть here "to eat" or "there is/there are"? How do I know?

The form есть can mean two different things in Russian:

есть – infinitive of есть "to eat"
есть – present tense form of быть meaning "there is/there are" or "is/are" (in some constructions)

In this sentence:

стараюсь есть меньше калорий – here есть can only be the infinitive "to eat" because:
- It comes right after стараюсь, which requires an infinitive.
- Semantically, "try to eat fewer calories" makes sense; "try there-is fewer calories" does not.

So context and the grammar pattern (verb + infinitive) tell you it is "to eat."

Why is калорий in that form? Why not меньше калории or меньше калорий in accusative?

Калорий is in the genitive plural. After меньше ("less / fewer"), Russian normally uses the genitive case:

меньше воды – less water (gen. sg.)
меньше людей – fewer people (gen. pl.)
меньше калорий – fewer calories (gen. pl.)

So the base word is калория (nom. sg.), and its genitive plural is калорий:

Nom. pl.: калории
Gen. pl.: калорий

The direct object of есть by itself would be in the accusative (есть калории), but once you add меньше, the whole phrase behaves like a quantity, and you switch to the genitive: есть меньше калорий.

Why is it меньше калорий, not менее калорий? Aren’t both "less"?

Both меньше and менее can translate as "less", but they’re used differently:

меньше:
- with quantities / numbers / countable things
- as an adverb meaning "less":
  - есть меньше калорий – eat fewer calories
  - работать меньше – work less
менее:
- with adjectives/adverbs in more formal or bookish speech:
  - менее калорийная еда – less caloric food
  - менее важный вопрос – a less important question

So with a noun like калории, you want меньше калорий, not менее калорий.

What does вечером mean exactly, and why is there no preposition like "в"?

Вечером literally is the instrumental singular of вечер ("evening"), but in practice it functions as an adverb of time meaning "in the evening".

Russian often uses bare case forms as adverbials of time:

утром – in the morning
днём – in the daytime
вечером – in the evening
ночью – at night

So:

Я ем меньше калорий вечером. – I eat fewer calories in the evening.

You could say в вечернее время, but that’s more formal and unnatural here. The standard everyday form is вечером without a preposition.

Can the word order change? For example, can I say Я вечером тоже стараюсь есть меньше калорий?

Yes, Russian word order is flexible, and several variations are possible, each with slightly different emphasis but all grammatically correct:

Я тоже стараюсь есть меньше калорий вечером.
– Neutral: "I also try to eat fewer calories in the evening."
Я вечером тоже стараюсь есть меньше калорий.
– Slightly emphasizes evening first: "In the evening, I also try to eat fewer calories."
Вечером я тоже стараюсь есть меньше калорий.
– Even stronger focus on "in the evening" as a contrast with other times.
Я тоже вечером стараюсь есть меньше калорий.
– Focus on "also in the evening (in addition to other times/other people)."

The original order is very natural, but these variants are all acceptable; Russian uses stress and context, not just position, to show emphasis.

Could I replace стараюсь with постараюсь here? What would change?

стараюсь – present tense, imperfective aspect; describes an ongoing habit or regular effort:
- Я стараюсь есть меньше калорий вечером.
  – I try (in general, as a habit) to eat fewer calories in the evening.
постараюсь – future tense, perfective aspect; usually about a single action or specific future effort:
- Я постараюсь есть меньше калорий вечером.
  – I will try (from now on / on a particular occasion) to eat fewer calories in the evening.

In your sentence, the idea is a habitual behavior, so стараюсь is better. Постараюсь would sound more like a promise or decision: "I’ll try to do this (from now on)."

Is there any difference between я не на диете and я не сижу на диете?

Both can translate as "I’m not on a diet", but:

я не на диете – neutral statement about your current state: "I’m not (currently) on a diet."
я не сижу на диете (from сидеть на диете) – more colloquial; emphasizes "I don’t keep/follow a diet" as an activity or lifestyle.

In this sentence, я не на диете is a simple factual background condition, which fits very well before Хотя…:

Хотя я не на диете, я тоже стараюсь…
– Although I’m not on a diet, I still try…

You could say Хотя я не сижу на диете…, but it sounds slightly more casual and focuses more on not following a diet plan, rather than just the state.