“I would like to have a nicer lifestyle but don’t know how I can afford it,” she said.

A Chinese consumption downgrade could be felt around the world. Chinese spenders have been a key driver of their country’s economic growth in recent years. China, in turn, has played a major role in global growth. Chinese consumers help global companies like Apple, General Motors, Volkswagen and many others. A consumption downgrade could also embolden Mr. Trump in his trade fight with China, as he gambles that Beijing can’t take much more economic damage.

On paper, the Chinese economy looks strong. Look closer, and the cracks begin to show. Retail sales this year have grown at their slowest pace in more than a decade. Wages in the private sector are growing at their slowest pace since the global financial crisis. The stock market has fallen by one-fifth.

Last week, JD.com, a Chinese e-commerce company, reported disappointing quarterly results. JD.com’s focus is providing China’s growing middle class with quality products. Investors are watching closely to see whether the Alibaba Group, China’s biggest online retailer, will report weak results as well on Thursday.

Long-term factors are driving down spending among young people in particular. The cost of education is going up. Housing in rich cities like Beijing has become unaffordable for many.

Housing is so expensive that Wang Jiazhi moved out of his own home. A 34-year-old semiconductor engineer in the southern city of Shenzhen, he bought a one-bedroom apartment in 2016. In addition to a mortgage of more than $700 a month, he needs to pay his relatives back for the money he borrowed for the down payment. So he rents his apartment and shares a four-bedroom apartment with nine other men. This way, Mr. Wang — who makes about $2,000 a month after taxes — saves $160 a month.

Like many Chinese men, Mr. Wang believes he needs an apartment in order to find a wife. But he is under so much pressure with his mortgage and debt, and with supporting his aging parents in the countryside, that he has had to postpone his plan for marriage. His prospects weren’t good anyway: To save money, he has stopped dating.

“I work long hours every day,” he said. “It makes me feel occupied.”

So the consumption downgrade is in. Even as China’s stock market has sputtered, shares in companies that make affordable staples like erguotou, a cheap hard liquor, and pickled vegetables have bucked the trend.