The key to the question lies in what era and cultural background the expert being asked belongs to. Today, the answer is affirmative: fruit is indeed a healthy food. But in other eras, nutrition and medical experts would have drawn completely different conclusions. Galen, a doctor in ancient Greece and Rome, and the personal physician to Emperor Marcus Aurelius, was convinced that fruit could cause fevers and thus harm human health. His father lived to be a hundred only because the old man had never eaten fruit in his entire life.
For centuries, Europeans clung to the view that "fruit produces bad juices that lead to typhus." This idea was widely disseminated in various medical books of the time. —However, this kind of rigid thinking is somewhat similar to today's situation, such as the current recommendations to "eat at least 5 servings of fruits and vegetables a day" and to "consume as much as 800 grams daily." As late as the 16th century, a French book warned people against eating cherries because they "attract insects, cause nausea, their juice is unhealthy, and they have no nutritional value." Therefore, many sensible and health-conscious citizens at that time had a fear of fruit, just as many people today have a fear of butter and eggs. These two foods, however, were then enjoyed in large quantities and were considered the most delicious and healthy of all!
The fate of vegetables was even worse than that of fruit. The reason might be the basic fact that they grow in dirty soil. On the tables of the scholarly class, there was simply no place for such "filthy refuse." In the 13th century, doctors solemnly warned the public: "Every fruit, every vegetable is a completely inferior food, because they can make people's blood dirty." Later, during the Renaissance, it was believed that vegetables were completely devoid of nutrition compared to meat. They believed that cabbage caused nightmares, beets were heating to the body, and carrots were hard to digest. In the current era, fruits and vegetables are considered healthy because they "contain vitamins"—but this is a characteristic that various organ meats also possess. We can see that people in every era concoct theories and painstakingly develop these speculations into so-called "established facts." To date, there is no experimental evidence to show that fruit is healthier or less healthy than any other food.
Furthermore, we should not overlook the human body's remarkable adaptability: the Eskimos eat almost nothing but meat and animal fat, and for countless generations, they have successfully endured the immense burden of extreme cold without advanced technology. For example, the Maasai people living in Africa consume only milk and cow's blood for most of the year. However, they are much taller and stronger than their neighbors. If it were true that people should only eat certain specific foods, then groups like the Eskimos and Maasai, who are so deficient in fruit and green vegetables, would have long disappeared from the face of the earth.