Nowadays, with the development of off-season cultivation technology, it is increasingly common to eat off-season vegetables like cucumbers and tomatoes, which were originally summer produce, during the winter. However, because off-season vegetables are grown in conditions that violate their natural growth cycle, their nutritional composition undergoes certain changes compared to seasonal vegetables. If one is unaware of these nutritional changes and does not take corresponding supplementary measures, it may have adverse effects on the body.
Currently, off-season vegetables are mostly grown in greenhouses. Due to factors like insufficient sunlight and poor ventilation, the quality of the vegetables is compromised. Relevant data shows that sunlight exposure in greenhouses is far less than in open fields, leading to insufficient photosynthesis in vegetables, which in turn results in lower levels of chlorophyll, vitamin C, and sugar content. For example, under normal growing conditions, 100 grams of cucumber contains 0.75 mg of chlorophyll, 16.2 mg of vitamin C, and 2.3 mg of sugar. In contrast, cucumbers grown in greenhouses contain only 0.36 mg of chlorophyll, 12.7 mg of vitamin C, and 1.7 mg of sugar per 100 grams.
At the same time, poor ventilation in greenhouses reduces the evaporation of water from the surface of vegetable leaves, which in turn decreases the absorption of mineral elements from the soil, leading to insufficient mineral content in the vegetables. For instance, 100 grams of cucumber grown in a field contains 235 mg of potassium, while one grown in a greenhouse contains only 168 mg. The field-grown cucumber has 20 mg of calcium and 0.9 mg of iron, compared to 12 mg of calcium and only 0.3 mg of iron in the greenhouse-grown variety.
On the other hand, the greenhouse environment makes it difficult for harmful substances to dissipate, leading to excessive levels of these substances in the vegetables. Taking cucumbers as an example again, the content of the harmful substance nitrite in field-grown cucumbers is 0.07 mg per 100 grams, while in greenhouse-grown cucumbers it is 0.08 mg. For arsenic, the field-grown variety contains 0 mg, whereas the greenhouse-grown one contains as much as 35.6 mg.
Furthermore, some farmers apply excessive pesticides, fertilizers, and even hormones or preservatives to off-season vegetables to shorten their production cycle or extend their shelf life, which can cause more serious harm to the human body.
Many households now primarily eat off-season vegetables during the winter, only occasionally consuming seasonal ones like radishes or potatoes. In fact, this practice is not beneficial to health.
According to research, radishes contain about 5 times more vitamin C than cucumbers, and their levels of calcium, iron, and phosphorus are higher than those found in cucumbers, pears, oranges, and apples. Potatoes are hailed as "the underground apple." They are not only rich in carbohydrates but also contain a good amount of protein and a small quantity of fat, as well as crude fiber, calcium, iron, phosphorus, vitamin C, vitamin B, and carotene. Every 100 grams of fresh potatoes provides 318 kilojoules of energy, which is more than double that of most grain foods. Therefore, when frequently eating off-season vegetables, one should not forget to pair them with seasonal vegetables and also consume foods rich in chlorophyll, such as sea algae, kelp, and fat choy (a type of cyanobacteria).
Finally, it should be noted that the heavy metal content and residual pesticide levels in off-season vegetables can be relatively high. Therefore, one should eat more foods that help detoxify. These foods include mung beans, black fungus (wood ear mushroom), pig's blood, apples, citrus fruits, and tea.
Black fungus and pig's blood have a strong laxative effect, and regular consumption can help expel most toxins from the intestines.
Eating apples, citrus fruits, persimmons, garlic, etc., is beneficial for detoxification and reducing lead absorption.
Eating mung beans can help counteract arsenic poisoning, so it is also recommended to drink some mung bean congee during the winter.
In addition, tea also has the effect of neutralizing metal toxicity. You can use an appropriate amount of tea to make a strong brew and drink 3 to 4 cups daily.
Experts point out that the mineral content in off-season vegetables is relatively low, and since vegetables are one of the main sources of minerals for the human body, it is important to supplement minerals when frequently consuming them. For example, you can eat more dairy products, dried shrimp, crispy fish, and egg yolks to supplement calcium; eat more whole grains, almonds, and walnuts to supplement magnesium; eat beans, bananas, and pig's kidneys to supplement potassium; and eat black fungus, animal liver, kelp, and sesame paste to supplement iron.