Therefore, international organizations and countries, including WHO, have called for reducing salt intake. At present, it is suggested that the daily intake of sodium should not exceed 2~2.3 grams (5~6 grams of salt). However, after years of education, the effect of reducing salt intake is not significant. Take the United States, where health education is prevalent, as an example. The latest survey shows that the average daily salt intake of residents is still as high as 8 grams or more.
Since most people know that a high-salt diet is harmful to health, why is it difficult to give up the hobby of salt? Known causes include congenital sodium appetite and acquired "heavy taste" eating habits.
Sodium appetite. Sodium is the main cation in extracellular fluid and an indispensable nutrient for human and animal survival. In the long-term evolution of human ancestors, the diet structure dominated by plant foods (low in sodium and high in potassium) created an innate hobby for sodium. Animal experiments show that normal rats have a preference for low-concentration saline, but have an aversion to high-concentration saline. After two days of strict sodium-free feeding, rats showed a strong preference for high-concentration physiological saline, which showed an increase in licking speed and food intake. After returning to a normal diet, this preference can even last for up to 3 months.
Humans also have this sodium appetite. Low-salt diet often makes people feel uncomfortable and leads to the impulse and behavior of compensatory increase in intake.
A "heavy taste" diet. People's eating habits are greatly influenced by regions, especially family traditions. "Mom cooks" is one of the vivid manifestations of this influence. Similarly, salt intake also has obvious regional and family habits. For example, the northern part of China is a region with high salt intake, and the salt intake of different families is significantly different. Moreover, once this habit is formed, it often lasts for life and is difficult to change.
In addition, a recent study has made a new discovery, observing that people's strong taste for salt is related to the mutation of the gene encoding taste.
The high-salt diet is partly due to the genetic variation of taste.
A preliminary study at the annual meeting of the American Heart Association in 20 16 found that the gene TAS2R38, which codes for bitter taste receptor, has a mutation. People who are more sensitive to bitter taste consume more salt than those who have another gene variant but are not sensitive to bitter taste, and the average consumption reaches 5.75g (2.3g sodium) which is 1.9 times the recommended amount of American Dietary Guidelines.
That is to say, it is not the mutation of salt receptor gene that affects sodium intake, but the mutation of bitter receptor gene, because this phenomenon is called taste masking. What the hell is going on here?
Human taste
At present, it is clearly known that human beings, like most other mammals, have five flavors: sweet, salty, sour, bitter and umami. Human ancestors ate almost everything on the earth as food, but they knew nothing about the ingredients and health effects of what they ate, and only relied on taste to identify it. The nutrients needed to maintain life are "set" into a good taste, resulting in a happy mood, such as sugar is sweet, amino acids are fresh and salt is salty; What may be toxic is set as bad taste, resulting in disgust. For example, the potential toxic substances such as alkaloids widely found in plant foods are bitter, and high-concentration salt is an annoying bitter salt.
Taste is mainly produced by taste receptors mainly existing in taste cells of oral mucosa (concentrated in taste buds). Due to the extensiveness of food and the complexity of food materials, taste receptors have different degrees of genetic diversity, especially in bitterness receptors.
It is known that the ligand of salty receptor is mainly sodium ion, and the receptor itself is a sodium ion channel, which allows sodium to directly enter the cell to depolarize and trigger action potential to generate electrical signals. Acid taste receptors detect hydrogen ions released by acidic substances, which can close transmembrane potassium channels, lead to cell depolarization, generate electrical signals and release neurotransmitter 5- hydroxytryptamine to convey sour taste. Sweetness and umami receptors are G-coupled proteins, belonging to the second and third sequences of the taste receptor 1 family, so they are named T 1R2 and T 1R3, and the corresponding genes are TAS 1R2 and TAS 1R3. These receptors bind to corresponding ligands and trigger action potentials by releasing intracellular calcium and sodium currents.
Bitter receptor is also a G-coupled protein, belonging to taste receptor 2 family, and its gene is named after "T2Rn" sequence. Because the main plant foods in the long-term evolution of human ancestors contain a variety of bitter substances, the bitterness is much more complicated. At present, it is known that there are 25 genes encoding different bitter receptors in human beings.
Among them, the bitter receptor with gene number TAS2R38 has been thoroughly studied, and it is mainly responsible for detecting the bitter substance of phenylthiocarbamate (PTC), which is widely found in Brassica plants, such as broccoli, cabbage, mustard and other vegetables. People with different TAS2R38 variants have different tastes for these substances. Some people will have obvious bitterness for low concentration PTC, while others will not have bitterness for high concentration PTC. Generally speaking, most people who account for about 75% of the population are sensitive to PTC, while the other 25% are not.
75% PTC-sensitive people eat higher salt to cover up their bitterness.
Taste masking
There has always been a misunderstanding about the taste perception of the tongue, saying that different areas of the tongue feel different tastes, which is the so-called "taste map"
In fact, taste buds are not the specificity of taste perception. Different parts of the tongue have different sensitivities to various tastes, but the types and density distributions of tongue papillae are different.
Each taste bud can feel different tastes at the same time. Taste is like a palette, which produces different tastes according to the chemical composition and content of different foods.
When two compound solutions contact the same taste bud at the same time, there may be interaction between the two compounds and the taste receptor, and one compound may enhance or inhibit the feeling of the taste receptor of the other compound, and then signal transduction occurs. The former is called flavoring. Common examples, such as salty taste, can enhance the feeling of sweetness. For example, eating watermelon with light salt water will make you feel sweeter, and adding salt to dessert cake will make you taste sweeter. The latter is called taste inhibition or masking. Bitter masking is of great value to improve the taste of oral drugs, so it has been widely studied. A common example is that sodium salt or zinc salt can inhibit the masking of bitterness at a certain concentration.
This is the basic principle that people who are sensitive to bitterness will eat more salt to cover up bitterness.
To sum up, high-salt diet is an unhealthy diet, and there may be many reasons for people to eat high-salt diet. However, modern medical research has provided enough information to guide our diet. In order to be healthy, our diet can no longer be driven by innate desires, but should follow scientific principles.
In short, it's not just salt. In order to be healthy, we can't just eat with our mouths, we should eat with our brains.