Nowadays, both people with abnormal blood sugar and healthy people attach great importance to dietary management, especially in the selection of staple foods, and pay attention to the combination of thickness and thickness. In the outpatient clinic, we found that although many people choose whole grains, their blood sugar fluctuates because of this. Why is this? Today, let me tell you how to scientifically distinguish between coarse grains and refined grains? What’s going on with “fake coarse grains”?
What is the difference in nutritional value between coarse grains and refined grains?
The folk classification of coarse grains and fine grains mainly depends on sensory perception: coarse grains are rough and dark in color, while fine grains are fine, soft and white in color. However, this division method is only based on experience and is sometimes inaccurate.
Coarse grains are a big family. There are three major categories of common coarse grains in daily life: whole grains, including rice (brown rice, purple rice, etc.), wheat, corn, barley, millet, sorghum, oats and buckwheat, etc.; miscellaneous beans, Including red beans, mung beans, kidney beans, peas, chickpeas and broad beans, etc.; potatoes, including potatoes, sweet potatoes (sweet potatoes, purple potatoes, etc.), yams, taro and cassava, etc. Simply put, coarse grains are a general term for grains other than polished rice and white flour.
Refined grains usually refer to rice (including glutinous rice) and white flour. In nutrition, rice and white flour are called “refined grains”, and their corresponding complete forms are brown rice and whole wheat flour respectively. Complete cereal seeds, called “whole grains”, consist of four parts from the outside to the inside: the bran, the aleurone layer, the germ (germ) and the endosperm. During the refining process of grains, the husk, aleurone layer and germ of grains that are rough in texture or contain more fat are ground away layer by layer, leaving only the endosperm, which is the innermost starch core.
In other words, the main difference between coarse grains and fine grains is not the different sensory experience, but the lower degree of processing and maintaining the natural intact form.
From the perspective of nutritional content, taking whole grains as an example, the husk mainly contains dietary fiber, B vitamins, minerals and phytochemicals; the aleurone layer contains more protein, fat, rich B vitamins and minerals; The cereal germ contains protein, polyunsaturated fatty acids, vitamin E, B vitamins and minerals; the endosperm mainly contains a large amount of starch and a small amount of protein. The types of nutrients contained in beans and potatoes such as carbohydrates, dietary fiber, protein, vitamins and minerals are generally similar to whole grains.
New research has found that phytochemicals contained in whole grains, such as anthocyanins contained in dark-colored whole grains such as purple rice and purple potatoes, are similar to purple cabbage and blueberries. They have powerful antioxidant effects and can help people remove toxins from the body. free radicals. The phytosterols contained in the bran, aleurone layer and germ can help lower blood cholesterol. These unique nutritional advantages in preventing chronic metabolic diseases are not available in refined grains or even animal foods.
It can “slowly raise blood sugar” but cannot “lower blood sugar”
Modern nutrition has fully affirmed the benefits of whole grains to human health, which are mainly reflected in three aspects: richer nutrition, smaller blood sugar fluctuations, and helpful for weight loss and laxatives.
Among them, “helping stabilize blood sugar” may be the main reason why people choose whole grains. So is this true?
In nutrition, the glycemic index (GI) is a measure of the postprandial blood sugar response caused by food. Generally speaking, foods with GI >70 are considered high GI foods, foods with 55 ≤ GI ≤ 70 are considered medium GI foods, and foods with GI <55 are considered low GI foods. The GI of food depends on the speed of digestion and absorption of carbohydrates in the food, that is, the degree of contact between the amylase in the digestive juice and the starch in the food within the same period of time.
Scientific data shows that under the same conditions, the glycemic index of whole grains is generally lower than that of refined grains. Whole grains raise blood sugar slowly, mainly for the following reasons.
First, dietary fiber itself cannot be broken down by digestive enzymes, and it can also reduce the degree of contact between amylase and starch, slowing down digestion.
Second, the physical structure is special, such as cooked rice, rice with mixed beans or steamed potatoes. Coarse grains are usually eaten in their original form. Even after chewing, the structure of the starch wrapped in the seed coat cannot be crushed as thoroughly as fine grains. The arrangement of starch molecules is also more compact than that of fine grains, making it difficult for them to fully contact amylase, thus slowing down digestion.
Third, because coarse grains contain more protein and fat than fine grains, they can not only prevent amylase from contacting starch, but also delay gastric emptying, causing starch to enter the small intestine more slowly for digestion. The three major energy-supplying nutrients have different effects on gastric emptying speed. Carbohydrates are the fastest, followed by proteins, and fats are the slowest.
In addition, it needs to be reminded that whole grains raise blood sugar slowly, but compared to refined grains, this does not mean that it can lower blood sugar. Some people think that as long as most or even all of the staple food is made from whole grains, it can replace the role of hypoglycemic drugs. This is not advisable. You must consult a professional doctor to adjust drug prescriptions.
If you cook improperly, you may end up eating “fake whole grains”
What needs to be reminded here is that the benefits of whole grains in controlling blood sugar levels do not occur “unconditionally”. It is also related to the cooking method.
In addition to what was mentioned above, the molecular type of starch also affects the speed of digestion and absorption. Amylopectin is digested and absorbed faster than amylose. Most grains are mainly amylose, but there are exceptions. For example, glutinous rice (GI=87) contains amylopectin, which can be made into rice dumplings, rice cakes, glutinous rice balls, glutinous rice cakes, etc., and has a sticky texture.
There are also varieties of whole grains that mainly contain amylopectin, which also have a sticky and waxy taste. Typical representatives are rhubarb rice, black waxy corn and waxy millet. Although they also contain dietary fiber and other nutrients, due to the influence of amylopectin, the glycemic index is higher than rice (GI=83) and steamed buns (GI=88). Rhubarb rice GI=111 and black waxy corn GI=106 , glutinous millet GI=108.
In addition, cooking and processing methods also have a certain impact on the glycemic index of whole grains. The cooking methods selected for some whole grains will cause them to have the same blood sugar-raising effect as refined grains.
1. Degree of gelatinization
That is, the degree of starch hydrolysis before consumption will affect the postprandial blood sugar response. Even whole grains have a higher GI if they are cooked too long.
2. Degree of crushing
If cereals, beans or potatoes are made into powder or puree, the original structure of starch wrapped in layers of dietary fiber will be destroyed, the starch will be fully exposed, and the GI will increase. For example, potato GI=62, while mashed potato GI=87.
Grinding whole grains into powder and compacting them into noodles, or fermenting them into steamed buns, will also significantly affect GI. For example, for the same whole wheat, the GI of wheat grains is 41, the GI of whole wheat noodles is 37, and the GI of whole wheat steamed buns is 82. You know, the GI of noodles made from white flour is only 41.
Therefore, if you want to control blood sugar, but choose to cook sticky rice, mashed potatoes or whole wheat steamed buns, it is no different from eating refined grains.
“Grinding it into powder” may not be healthier for consumption
I believe many people have seen product promotions in supermarkets or online stores that say “whole grains are ground into powder and eaten more healthily”, but what is the reality?
Grinding coarse grains into powder destroys the physical structure. If eaten in a short period of time, the nutrients will not be lost too much. However, if stored for a long time, some phytochemicals or vitamin E and other nutrients with antioxidant effects will be exposed to oxygen for too long. When oxidized, the nutritional value will decrease.
As for whether it is healthy, specific issues need to be analyzed in detail. People who are frail, malnourished or have poor digestive function have difficulty fully digesting and absorbing the nutrients in the original form of whole grains. Choosing whole grain powder is equivalent to partially replacing the oral chewing and gastrointestinal digestive functions, which is beneficial to nutrient absorption. If you have high blood sugar or are obese, you are not suitable to choose whole grain powder, as it will weaken the effect of assisting in controlling postprandial blood sugar or reducing fat synthesis. For people with constipation, whether the whole grains are ground into powder or not, it will not affect the laxative effect of the dietary fiber in the whole grains.
Why does whole grain meal increase the glycemic index of food? This is because the starch molecules inside the coarse grain particles are arranged neatly and tightly, and are wrapped by the seed coat and internal dietary fiber, protein and other components. Water is not easy to enter the inside, and the starch is not easy to absorb water, expand and gelatinize. However, after the whole grains are ground into powder, the physical structure of the layers of packaging is broken, and the starch is fully exposed. After being boiled or brewed with hot water, it is easily digested and absorbed after eating. Therefore, the glycemic index of whole grain powder is significantly higher than that of whole grains in their original form. For example, the GI of red beans is only 23, but after being ground into powder, it can reach 72-75, immediately changing from a low GI food to a high GI food.
Therefore, in order to control sugar or lose weight, eating whole grain powder is not as good as eating whole grain whole grains. If you don’t like the taste of whole grains and eat very little or have no chance to eat whole grains, you can choose to eat whole grain powder in order to achieve your daily intake of whole grains or to relieve constipation.
To “control sugar” in your diet, you should not only eat whole grains
Whole grains are good, but too little is too much. People with high blood sugar who only eat whole grains for a long time will put too much burden on the digestive system and increase the risk of gastrointestinal diseases. At the same time, dietary fiber, phytic acid and other ingredients in whole grains will also reduce the absorption rate of dietary minerals. There is a risk of malnutrition.
For healthy people, a combination of coarse grains and refined grains is the most nutritious. The “Dietary Guidelines for Chinese Residents (2022 Edition)” recommends that healthy adults need to maintain 1/4-1/2 of their daily staple food (200-300g) as whole grains or miscellaneous beans (50-150g), potatoes Take 50-100g per day. If it is to control blood sugar or lose weight, you can follow the upper limit of the above ratio, that is, 1/2 of the daily staple food should be whole grains or mixed beans, and 100g of potatoes.
As for diabetic patients, choosing low GI foods as staple food can only play a partial role. In addition, they need to pay attention to the dietary structure, that is, a reasonable combination of staple food with meat, eggs, milk, soy products, vegetables and oils. The GI of mixed foods is generally lower than that of pure whole grain staple foods. The reason is that the human body consumes more protein, fat and dietary fiber after mixing than pure whole grains. For example, the GI of rice is 83, while the GI of rice + fish is 37, and the GI of rice + fried pork and celery is 57; the GI of steamed buns is 88, while the GI of steamed buns + beef with soy sauce is 49, and the GI of steamed buns + fried eggs with celery is 49. ; The GI of pork stewed vermicelli is as low as 17.
In other words, even if you choose high GI refined grains, through a reasonable combination of protein, fat and vegetable fiber, you can achieve the effect of slowly raising blood sugar similar to that of coarse grains. Of course, if on this basis, the staple food can be matched in thickness, then the GI of the mixed food will be more conducive to blood sugar stability and health. (Author: Yu Yongchao, nutritionist, China-Japan Friendship Hospital)