“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're introducing the topic. You write:

Over one in five Americans suffer from obesity.

over (#)

In writing or formal speeches, you use "over" to mean "more than" some number:

Over 20% of our employees have Master's degrees or Ph.D.'s.

Over 500 people have signed up to volunteer.

(#) in (#)

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.

(people) suffer from obesity

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.