The digestive system can cause problems for many in summer. Some lose their appetite while others suffer bouts of diarrhea. Traditional Chinese medicine recommends foods to benefit the digestive system in summer, letting you avoid the problems and giving you a stronger spleen and stomach.

TCM has a lot to say about this zhu xia, or "summer sickness," which arrives in warm weather and departs when it cools down. The main symptom is loss of appetite - and TCM stresses the importance of regular meals.

Prevailing pathogenic dampness in summer is the main external cause of digestive problems, according to TCM. When pathogenic dampness invades, the stomach (digestive system) and spleen (converts food into energy) are usually the first to be attacked and begin to function poorly.

Apart from a poor appetite and indigestion, inflammation in the digestive system can happen easily with a weak spleen. Some foods such as lotus roots, purple haricots (beans) and crucian carp are recommended as they help dispel pathogenic heat and strengthen the spleen and stomach.

There are many other yin ("cold" energy) foods that can help, including tomatoes, apples, pears, watermelon, fungus, cucumber, chrysanthemum, yam, sweet potatoes, pearl barley, millet, mung beans, seaweed and white gourd.

Lisa Chen, a 23-year-old student, says her stomach went "on strike" recently. She doesn't feel like lifting her chopsticks, not even for her favorite fried chicken wings. It happens every summer.

"Whenever the weather gets hot, I started to lose my appetite, and sometimes tire easily," says Chen. "I don't push myself to eat when I have no appetite. My mom says it's no big deal, just zhu xia, which she suffered from for a couple of years.

She's glad to lose weight in the easy, no-will power way, but TCM doctors warn that irregular eating habits undermine the digestion and aggravate existing problems. Lack of nourishment can cause dizziness and fatigue.

Zhu xia is common in warm weather, especially in southern China that has a hot and damp climate, says Dr Zhang Zhenxian, chief physician of the Special Needs Department of Yueyang Hospital.

"Summer sickness is more likely to affect vulnerable people, especially the elderly and children," he says. The most common symptom is loss of appetite; some people feel dizzy, weak, get headaches and feel chest pains. Women are more likely to suffer than men.

Summer sickness does not manifest itself with particular organ problems. It just comes in summer, disappears in fall and may recur in the next summer.

Generally speaking, the main cause is pathogenic heat and damp, which are strong in summer. These pathogenic energies easily "invade" weak people who feel ill when their body cannot adjust to the new hot and damp internal environment.

The spleen and stomach are usually the first to be attacked. Iced or cold drinks aggravate the problem, though they make people feel cool temporarily.

"Sweating is the major way for the human body to dispel internal heat," says Zhang.

"Iced drinks prevent people from sweating, usually leading to accumulation of pathogenic internal heat. "Foods that are 'cold' and reinforce yin energy are not cold in temperature, and are recommended for summer sickness."