Because a "diet" isn't something you go on and go off of, like a prescription.

因为饮食并不是像处方一样你必须遵守的规定。

youdao

He had never been afraid of failure: he was a gambler, ready to go off somewhere else and start all over again.

他从不害怕失败：他是个冒险家，随时准备去别的地方重新开始。

《柯林斯英汉双解大词典》

We decided to write off the rest of the day and go shopping.

我们决定放弃那天余下的时间而去购物。

《柯林斯英汉双解大词典》

The core of the comic book character is there, but we kind of go off on all these different tangents."

VOA: standard.2010.06.20

When demons are cast out by the apostles and sent into a herd of pigs, and the pigs go running off a cliff and die; that's one image.

第一个是魔鬼们被使徒们赶出了天界,赶到了一群猪的中间，然后那些猪就跑向了悬崖,摔死在了那里。

耶鲁公开课 - 1945年后的美国小说课程节选

You are about to go off on Friday night to see these movies and let's allow some communication ahead of time.

现在你们约好了周五晚上一起看电影,你们可以先沟通一下

耶鲁公开课 - 博弈论课程节选

The packaging is all we have to go off of at this point -- Samsung reps we spoke to didn't know to expect the device today, so there's no pricing or availability info to share.

ENGADGET: Samsung HM5100 Bluetooth S Pen makes a surprise debut in our Note 10.1 'press kit,' we pencil in a chat (hands-on)

Coroner Andrew Tweddle found the soldier fired the fatal shot himself, and that the gun did not go off because of a malfunction.

BBC: Huddersfield soldier's inquest records open verdict

What this allows us to do of course is to go off into paroxysms of speculation as to what might be on the new systems.

FORBES: Links 2 Jan: Apple's iPhone 6 And iOS7 Already Showing Up