Boys and girls tend to show the physical changes of puberty starting at age 10, but a 13-year-old boy in China got an unexpected surprise when he began to grow excess breast tissue. Six years later, the patient, nicknamed “Xiao Fang,” has undergone a mastectomy to remove his A-cup breast, which doctors have linked to fast food.

Feng's breast growth is believed to be due to a hormonal imbalance brought on by the "gender bending" chemicals in fast food. Doctors at China’s Zhejiang Wenzhou Central Hospital found Feng's body to be in otherwise perfect condition.

"The right side of the patient's body resembles a woman, while the left a man," Chief of Medicine Pan Zhongliang told the Qianjiang Evening Post, the DailyMail reported.

The condition is referred to as gynecomastia, which is characterized as the swelling of the breast tissue in boys or men, and is linked to an imbalance of the hormones estrogen and testosterone, according to Mayo Clinic. The condition is commonly found in newborns, boys going through puberty, and older men who develop it as a result of normal changes in hormone levels. Gynecomastia can go away on its own, but in Feng's case, surgery was the best option to reduce breast tissue.

In the United States, surgery to correct gynecomastia can cost between $3,000 to $10,000, and is not covered by insurance because it's not deemed medically necessary. Yet, gynecomastia-related surgeries have risen by 36 percent since 2000, according to the American Society of Plastic Surgeons. Dr. Adrian Lo, a plastic surgeon who specializes in gynecomastia in Philadelphia, P.a., performs four or five of these procedures a week.

“The men I see are usually pretty fit,” he told Men's Health. “But most men with gynecomastia qualify for surgery even if they’re not an ideal weight.”

There are men who develop pubescent gynecomastia, which can not go away naturally, like Feng. Typically, the testicles produce both estrogen and testosterone, but in early puberty, some boys may not have enough free testosterone to counteract the estrogen. This hormone imbalance is reflected by the growth of breast tissue.

Certain foods are linked to these imbalances, which can lower testosterone and raise estrogen levels, causing male breast tissue growth. For example, a high-fat, high-carbohydrate diet can lead to body inflammation, increasing estrogen levels and breast tenderness. High-carbohydrate, fatty foods include pastries, french fries, milkshakes, and fried chicken.

Similarly, medications can also affect the growth of breast tissue in men. A study published in the journal American Family Physician found up to 25 percent of gynecomastia cases are caused by meds. Antidepressants, antipsychotics, cholesterol drugs, hair loss treatments, and anabolic steroids, among many more, lead to breast tissue enlargement.

Feng's unnecessary breast tissue was removed in a mastectomy. He remained in the hospital several days later to recover and was discharged from the hospital five days later. According to Pan, excess breast tissue is not likely to grow back after the surgery. The final results of gynecomastia surgery may take three to six months to achieve; incision lines are permanent, but will continue to fade over time.

Feng will now be able to resume activities like swimming and playing sports with friends without his breast getting in the way.