“Over one in five Americans suffer from obesity.”
You're writing a blog post about how you think America should solve the problem of having too many overweight people. You write this in your introduction of the topic.
Over one in five Americans suffer from obesity.
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You can use "1 in 10" to mean 10%, "2 in 100" to mean 2%, and so on. People usually express numbers in this way in writing or when speaking about a topic that they've researched and are prepared to talk about.
When a person has a long-term health problem, you say that they "suffer from" that problem:
suffer from depression
suffer from insomnia (not being able to sleep)
suffer from lower back pain
"Obesity" means being very, very overweight. "Obesity" is a technical term that is used by doctors, but normal people also use it when talking about fatness as a general problem:
Obesity is a serious problem in the U.S.
In writing or formal speeches, you use "over" to mean "more than" some number:
There must have been over a thousand people there.
Over 20% of our employees have Master's degrees or Ph.D.'s.
Over 500 people have signed up to volunteer.
It's used in both spoken and written English, but in writing it's probably more common than using "more than".