Feeling tired lately? Has the doctor said he can’t find anything wrong with you? Perhaps he sent you to a hospital, but all the advanced equipment there shows that there is nothing wrong.

Then consider this, you might be in a state of subhealth（亚健康）.

Subhealth, also called the third state or grey state, is explained as an indefinate state between health and disease. According to an investigation by the National Health Organization, over 45 per cent of subhealthy people are middle-aged or elderly. The percentage is even higher among people who work in management position as well as students around exam.

Symptoms（症状）include a lack of energy, depression, slow reactions, insomnia（失眠）,Worries and poor memory. Others symptoms include shortness of breath, sweating and aching in the waist and legs.

The key to preventing and recovering from subhealth, according to some medical experts, is to form good living habits, alternate work with rest, exercise regularly, and take part in open-air activities.

As for meals, people are advised to eat less salt and sugar. They should eat more fresh vegetables, fruits and fish, because they are rich in nutritional（营养的）elements—vitamins and tiny elements—that are important to the body.

Nutrition experts point out that it is not good to eat too much at one meal because it may cause unhealthy changes in the digestive tract. They also say that a balanced diet is very helpful in avoiding subhealth.

1.According to this passage, when you are in a state of subhealth, you should       .

2.Middle-aged people may feel subhealthy, because they       .

3.As for food, experts suggest that we should        .

4.The underlined word “alternate” in this passage means        .