몸짱 열풍, flab(군살), crash diet(갑작스럽게 살 빼는 것), make no bones about

a knockout body.

1. A very attractive woman. So named because her attractiveness is so stunning that it can (figuratively) knock you out. (make you speechless, stutter, etc.) Hence the term "knockout." 
2. A punch in boxing that knocks your opponent unconscious, typically ending the match.

Guy1: Wow check her out! 
Guy2: Yep, she's a knockout all right. 

얼짱: a shortened Korean slang for a pretty[good-looking] face.

몸짱: a knockout body.(보통 여자들에게 사용함)

sedentary (adj.) 

1590s, "remaining in one place," from Middle French sédentaire (16c.) and directly from Latin sedentarius"sitting, remaining in one place," from sedentem (nominative sedens), present participle of sedere "to sit; occupy an official seat, preside; sit still, remain; be fixed or settled," from PIE root *sed- (1) "to sit" (cognates: Sanskrit a-sadat "sat down," sidati "sits;" Old Persian hadis "abode;" Greek ezesthai "to sit,"hedra "seat, chair, face of a geometric solid;" Old Irish suide "seat, sitting;" Welsh sedd "seat," eistedd"sitting;" Old Church Slavonic sežda, sedeti "to sit;" Lithuanian sedmi "to sit;" Russian sad "garden," Lithuanian soditi "to plant;" Gothic sitan, Old English sittan "to sit;" see sit). Of persons, the sense "not in the habit of exercise" is recorded from 1660s.

flab(군살)

extra soft flesh on a person's body : excess body fat

a fight against flab = 살과의 전쟁.

shed extra pounds = 군살을 빼다. 

carry extra weight around the middle or thighs

(복부나 허벅지에 군살이 있다.)

stave off weight gain: 체중 증가를 사전에 방지하다.

A crash diet is a method to lose weight really fast in a short period of time, by reducing the daily calorie intake to as low as 700 calories a day.

brisk walking: 빠르게 걷는 것.

There is a real disconnect between what we know and what we do.

(아는 것과 행하는 것은 전혀 별개의 일이다.)

the stress on the joints: 관절 부담.

Korean society is gripped in the irrational frenzy to get the title of 얼짱 and 몸짱.

(한국 사회는 심각한 얼짱, 몸짱 병에 걸려 있다.)

It will be a huge problem if society at large tends to deride and even attach a stigma to pot-bellied people with a less than an ideal body as lazy people or couch potatoes.

(뱃살이 많고 체형이 완벽하지 않은 사람을 사회가 나서서 웃음거리로 만들거나 게으른 사람으로 낙인찍는 것은 옳지 않다.)

deride = 얼레리 꼴레리 하는 것이다.

Still worse, some celebrities on TV shows make no bones about making fun of those with below-average looks.

make no bones about ~: ~에 대해 거리낌이 (없다, 이야기하다, 표현하다.)

to say clearly what you think or feel although you may embarrass or offend someone 

He made no bones about his dissatisfaction with the service in the hotel. 

She makes no bones about wanting John to leave.

 He made no bones about how bad he thought the food was.

What matters most is how to cultivate our inner qualities and strengths.

(가장 중요한 것은 내적인 자질이나 강인함을 개발하는 방법이다.)