When it comes to dietary fiber in food, people often think of the strands in celery, the stalks in Chinese cabbage, and the fibers in chives. Once, during a television program, I asked the audience which vegetable had the highest amount of dietary fiber, and most people chose celery, while the rest chose chives. When asked why they made those choices, they said it was based on what they heard from experts on TV.
I found that the misconception that vegetables with "fibers" are the main source of dietary fiber is quite common. So, let's start with the definition of dietary fiber.
Dietary fiber includes all food components that cannot be absorbed in the small intestine and can enter the large intestine. It mainly consists of various non-digestible carbohydrates, including cellulose, hemicellulose, various plant gums and microbial gums. It also includes substances like sugar alcohols and oligosaccharides, as well as resistant starch that cannot be digested and absorbed in the small intestine.
Looking at this definition, we can see that the key factor for dietary fiber is whether it can be digested and absorbed in the small intestine and whether it can enter the large intestine. Whether a food gets stuck in your teeth or irritates your throat is not a criterion for evaluating dietary fiber. Therefore, a food that appears to have fibers does not necessarily mean it is high in fiber, and a food without fibers that is not irritating to the throat does not mean it has a low fiber content.
So, which vegetables are really high in fiber？
The "fibers" in vegetables are the plant's vascular bundles, which are like the "blood vessels" of plants. Through these tough, fibrous tubes, plants transport nutrients from the roots to the upper parts and transport the nutrients synthesized in the leaves to the lower parts.
However, having these fibers does not mean that the fiber content is high. For example, Chinese cabbage, despite having fibers, has a low fiber content in most parts, with an average fiber content of only 0.8%. On the other hand, vegetables without fibers may have a higher fiber content.
For example, various tender beans and pods are high-fiber foods. Although boiled edamame has a soft texture, it doesn't prevent it from being the champion in vegetable fiber content (4.0%). Tender fava beans (3.1%) and tender peas (3.0%) have a delicate and delicious texture, while green beans are also crispy (1.5%), but their fiber content is much higher than that of celery stalks (1.2%). Even the legendary high-fiber vegetable, chives, has a fiber content of only 1.4%.
In addition to tender beans, vegetables like mustard greens (1.6%), spinach (1.7%), amaranth (1.8%), and broccoli (1.6%), which don't appear to have fibers, also have higher fiber content than celery stalks (1.2%).
Generally, for tender stems, leaves, flowers, and buds vegetables, wild vegetables have higher fiber content than cultivated vegetables, and dark green vegetables have higher fiber content than light-colored vegetables. For example, Chinese cabbage has a fiber content of 0.8%, while dark green bok choy and rapeseed have a fiber content of 1.1%. Cauliflower has a fiber content of 1.2%, while green broccoli has a fiber content of 1.6%, and crisp lettuce has a fiber content of only 0.6%.
If we talk about vegetables with low fiber content, it is usually fruit-like vegetables, such as tomatoes (fiber content 0.5%), cucumbers (0.5%), and winter melons (0.7%).
The characteristic of fiber that cannot be digested by the human small intestine does not change with physical processing. Chopping or boiling will not destroy the fiber. Therefore, high-fiber foods can still be used as fillings, which may be easier for the elderly and children to eat, but it will not affect the physiological effects of dietary fiber.
If fiber could be absorbed and utilized by the human body when it is chopped, the world would probably undergo a huge change - agricultural production could be greatly reduced. If chopped grass roots and bark could be made into food with some seasoning, supplying nutrients, why bother with the laborious production of grains?
Dietary fiber is divided into insoluble fiber and soluble fiber. Insoluble fiber tends to feel "rough" and can cause a feeling of reluctance when eaten. However, it is not difficult to change this feeling. Insoluble fiber likes oil. No matter how coarse a fiber-rich ingredient is, as long as it is simmered or soaked in oil, it will become soft and not irritate the throat.
Among different oils, semi-solid oils rich in saturated fats have a better effect than liquid oils with unsaturated fats. Therefore, high-fiber ingredients tend to go well with fatty foods. Southerners stew preserved vegetables with fatty pork belly, while northerners use fatty minced meat with preserved mustard greens to make dumplings. For example, high-fiber whole wheat biscuits are very palatable because they contain a large amount of saturated fat.
However, if we only pursue the comfort of eating high-fiber foods, we may fall into the trap of commercial products. Many cookies and pastries claim to be "high-fiber" or "bran," but they are still crispy and delicious. Such products usually have a high fat content, ranging from over 20% to over 30%.
While it is good to consume some fiber, having a high amount of saturated fat accompanies it, and the benefits are often overshadowed by the disadvantages. If you want to really cleanse your intestines with fiber, it is better to use low-fat cooking and processing methods.
