Well, yesterday I started to thinking about my health,. I've been thinking about how terrible my diet can be sometimes.

When the quarantine started, I didn't plan what would I do with my diet, so I ate whatever was much easierst in the moment.

TogglAlternating between fast- foods and normal's ones food, I didn't figured out how terrible Irealize how bad it was goetting.

Before the quarantine, I was training to run a half of a marathon, so I was running about 10 km two or three time a week.

Today I can't run plusmore thean 8 km.

I know that I can't do more because my conditional physic, thataerobic fitness, which I didn't train during this period, is not the best.

I took a guess at what you meant by "conditional physic" but I might have guessed wrong. Aerobic fitness, or cardiovascular fitness, is the type of fitness developed by endurance exercise such as running, cycling, swimming. It works your heart and lungs.

But if I restart the training with seriously again, I will achieve my last result or much morebe as good as before or even better.

My body can't stand atolerate training for too long because onwith my diet I haven't the leastdon't have enough nutrients to do harddemanding sports.

So if I want to do anything, first I need to change imy diet.

It wasn't necessarily wrong, but I think it would be better style here to be more clear about "it."

When the quarantine started, I didn't plan what I would I do with my diet, so I ate whatever was much easierst in the moment.

Toggling between fast-foods and normal's ones I didn't figured out how terrible I was goeating.

no need for the 's on normal. There is no possession going on here.

Before the quarantine, I was training to run a half of a marathon, so I was running about 10km two or three time a week.

Half marathon is used as an expression. It's never half of a marathon although this seems like it would make more sense.

Today I can't run plusmore then 8km.

In English we never say plus than

I know that I can't do more because my conditional ing/physic, that I didn't train in this period, is not the bestque is not the best because I didn't train much.

Conditioning, physique, or endurance are all applicable here

But if I restart the training with seriously, I will achieve my last result or much more.

we don't say with seriously in English

My body can't stand a training too long because oin my diet I don't haven't the least nutrients to do hard sports.