消瘦 (xiāo shòu) means “lose weight”

More examples

她因为工作太忙，脸色差，而且开始消瘦。tā yīn wèi gōng zuò tài máng liǎn sè chà ér qiě kāi shǐ xiāo shòu

She has a poor complexion because she is too busy with work, and she is starting to lose weight.

A gradual loss of flesh that leaves the body or face thin and worn.

瘦shòu: Grow thinner when the body loses some fat or flesh.
减肥jiǎn féi: Reduce body weight on purpose through planned eating or exercise.

指因疾病、精神压力或长期劳累导致身体或面容逐渐消瘦、显得憔悴。zhǐ yīn jí bìng jīng shén yā lì huò cháng qī láo lèi dǎo zhì shēn tǐ huò miàn róng zhú jiàn xiāo shòu xiǎn de qiáo cuì

消 (xiāo, "diminish") + 瘦 (shòu, "thin") presents flesh gradually disappearing until a person looks gaunt.

In everyday conversation, this verb often sounds like an observation about a person's health or condition, so it can carry concern rather than a neutral comment about body size.