Will overeating delicious food make your liver become as sticky as dough?

Recently, Nature magazine published a very unique article that discussed the relationship between the "viscoelasticity" of the liver and diabetes and cancer.

Many people in the food industry are very familiar with the term viscoelasticity, because it is an important texture property of dough made from wheat flour and water.

The dough is extensible, sticky and elastic. The kneaded dough is a little sticky but very elastic. It can be stretched into noodles or made into expanded and porous bread; it can be baked into crispy biscuits or made into sticky and elastic dumpling wrappers.

It can be said that it is precisely because of its viscoelasticity, and the fact that the degree of viscoelasticity can be easily adjusted, that this unique property makes dough a food ingredient that is loved by everyone in the world and can be made into tens of thousands of different kinds of food.

However, it is really rare that medical professionals actually talk about the viscoelasticity of the liver of living animals.

Researchers have found that the “touch” of the liver of people with diabetes has changed. Although it has not yet reached the level of hardening, it is more viscoelastic than that of healthy people[1]. Why does the liver of people with diabetes become more “viscoelastic”?

It may be that AGEs, the aging component, damages the liver

What is the difference between diabetics and healthy people? They have more sugar in their blood, higher levels of glycosylated hemoglobin, and more advanced glycation end products (AGEs) in their bodies.

Research has long found that AGEs are a type of component that promotes aging. The amount of AGEs in the human body is closely related to the occurrence of serious diseases such as diabetes, chronic kidney disease, atherosclerosis, Alzheimer's disease, and skin aging [2]. Recent studies have found that by measuring the content of AGEs in the skin, the risk of cardiovascular and cerebrovascular disease and the risk of diabetes can be predicted [3]. At the same time, more than half of diabetics have fatty liver problems , and high fat levels in the liver will also affect its texture.

There are two sources of AGEs in the human body. One is from the Maillard reaction between blood sugar and proteins in the body, which is called "self-made AGEs"; the other is from AGEs ingested from food, which can be called "exogenous AGEs".

Do AGEs in food really affect liver health?

To verify the relationship between AGEs and liver viscoelasticity, the researchers of this new study conducted animal experiments, feeding mice with feed rich in AGEs to see what changes would occur in them.

The results really showed that the livers of mice fed a high-AGEs diet gradually underwent changes similar to those of people with type 2 diabetes - not only did the liver develop insulin resistance, but the texture of the liver also changed, becoming more viscoelastic, which was largely caused by the cross-linking of collagen .

Worst of all, researchers have found that this change in liver viscoelasticity is accompanied by the activation of certain metabolic pathways, which can increase the risk of cancer even without cirrhosis. If AGEs are controlled, this risk can be reduced.

This study once again strongly suggests that AGEs in food can indeed be absorbed by the human body, and eating too much will cause harmful metabolic changes .

What foods are high in AGEs?

In our daily food, fried foods, processed meat products, high-temperature roasted cereal foods, roasted or fried nuts, and cooking oils that have been processed at high temperatures are all important sources of AGEs.

A survey conducted among Chinese residents found that in a pure Chinese diet dominated by starchy foods, staple foods contribute the most to AGEs intake, followed by meat and meat products. In a Western diet, in addition to cereal products and meat products, bread, cakes and biscuits are also important sources [4]. A survey found that nuts and roasted foods (fried or roasted peanuts, walnuts, almonds, etc.) and seasoning oils (sesame oil and chili oil made by stir-frying and frying) are also important sources of AGEs in the diet [5].

Increasing cooking temperature and time will produce more AGEs

For example, the content of CML (a major AGEs compound) in raw chicken was measured to be only 769 kU/100g;

But after grilling , the content rises to 4848 kU/100 g.

The content in raw steak is 800kU/100g.

The kU content of olive oil after frying is 10058 kU/100g[6].

Therefore, when cooking fish, meat and eggs, if you can lower the heating temperature and make them more tender, AGEs will be greatly reduced.

For example, when frying eggs in olive oil,

If fried on medium-low heat for 2 minutes , the CML content is only 97 kU/100 g;

Frying it over high heat for 1 minute will raise it to 243 kU/100 g.

Similarly, scrambled eggs over medium-low heat for 2 minutes only contained 63 kU/100 g of CML;

If stir-fried over high heat for 1 minute, the level will rise to 123 kU/100 g.

The same rule applies to cooking meat, grilling, etc. The higher the temperature and the longer the time, the greater the production of AGEs.

Why is this so? Because AGEs are the end product of the Maillard reaction . The speed of the Maillard reaction increases with the increase of temperature, and it also increases when the water content decreases. Therefore, in fresh foods such as milk, fresh eggs, raw fish, and raw meat, there is almost no Maillard reaction, and the content of AGEs is very low. But after heating and cooking, the content will increase significantly. Moreover, as the heating temperature increases, the production speed becomes faster and faster.

Foods that are more likely to produce AGEs

From the perspective of food composition, studies have found that foods rich in protein and fat are particularly prone to produce AGEs after heating, and even produce more AGEs than foods rich in starch alone. For example, the CML content in roasted almonds and roasted cashews is as high as 6650 and 9807 kU/100g, respectively, which is much higher than that of baked potatoes roasted for 45 minutes (218 kU/100g) [7].

This is because the Maillard reaction starts with a reaction between a carbonyl group and an amino group, where the amino group comes from protein amino acids and their decomposition products, and the carbonyl group comes from carbohydrates (especially small molecule sugars) and the oxidation products of fats. Under high temperature conditions, fat oxidation is very fast, and even in the absence of sugar and starch, it can provide the carbonyl group required for the Maillard reaction[8].

In a sense, these data can explain why eating roasted nuts and roasted nuts is particularly likely to increase inflammatory responses, causing sore throats, dry mouth and tongue, acne and blisters, and other "heaty" problems . Because although roasting increases the aroma and makes the taste crisper, it will produce a large amount of pro-inflammatory substances such as AGEs and acrylamide.

Delicious nuts such as peanuts, cashews, and almonds contain more than 20% protein, more than 40% fat, and about 20% carbohydrates. Together, they are an ideal matrix for the Maillard reaction to fully occur after heating.

Early studies have found that foods that have been processed with high temperatures, such as frying, roasting, or deep-frying until they are brown and have a strong flavor, will have a significant increase in AGEs content. For example, brown, fragrant, and crispy foods such as roasted chicken skin, roasted duck skin, and fried pork skin theoretically have the highest AGEs content.

Because they meet several conditions for the production of a large number of AGEs:

1. Rich in protein . Although the protein quality of meat skin and chicken skin is not high enough and is mainly collagen, they have a strong ability to undergo the Maillard reaction. This may be because collagen contains hydroxylysine, and this amino acid contains free amino groups, which causes the Maillard initiation reaction to occur very quickly.

2. Contains more fat . There is abundant subcutaneous fat under the skin of animals. The unsaturated fatty acids in the fat quickly undergo fat oxidation when roasted, grilled, or fried at high temperatures, which can provide more small molecular carbonyl compounds for the Maillard reaction. The unsaturated fatty acid content in chicken and duck is higher than that in pork, beef, and mutton. In theory, it is more likely to oxidize at high temperatures.

3 Before cooking or grilling, it is usually marinated to provide the sugar that is lacking in meat . Before roasting chicken, roast duck, roast meat, or roast fish, sugary seasonings (such as cooking wine, oyster sauce) are often added for marinating, or honey or maltose is applied on the surface (such as roast duck, roast suckling pig, etc.) to promote the Maillard reaction and increase the aroma, which also increases the content of AGEs.

4 After being heated at high temperature , with little moisture and a brown color, it indicates that the Maillard reaction is particularly violent and thorough.

Nowadays, many chefs like to add more sugar to dishes, which is to take advantage of the principle of promoting the Maillard reaction. Of course, this will also bring more AGEs.

For example, Cola Chicken has a burnt brown appearance and a sweet and fragrant taste...

For example, the Kung Pao pork cubes have a sweet and salty taste, with a little bit of burnt meat, and lots of crispy fried peanuts...

Ways to avoid excess AGEs

The content of AGEs in fresh, natural, high-water-content vegetables, fruits, fish, meat, eggs and milk is negligible, and the content in steamed and cooked foods is also very low . Because under the conditions of large amounts of water and low-temperature processing, the Maillard reaction occurs very slowly, and the production of AGEs is very small.

Therefore, one of the requirements of the "Oriental Healthy Dietary Model" is to lower the cooking temperature, use more steaming, boiling and stewing, and less frying, deep-frying, smoking and grilling. One of the scientific meanings is to reduce the intake of AGEs in the diet.

Therefore, the first way to reduce AGEs is to avoid eating too much high-temperature processed food. Eat more fresh and natural food and lower the cooking temperature.

The specific operation method is as follows:

- Do not use bread, fried dough sticks, fried cakes and other foods cooked at high temperatures as staple foods. Eat steamed buns, rice, boiled noodles, porridge, etc.

——Eat less fried and grilled food, and increase the proportion of steamed, boiled and stewed dishes.

——Keep the oil temperature lower when cooking, make the eggs more tender when frying, and reduce the number of over-frying operations.

- Eat fresh meat and fish, and do not often eat cured meats, processed meat products, salted fish, dried fish, etc.

——Eat less fried, roasted, or roasted nuts. Try to eat fresh, unroasted walnuts. Eat spiced boiled peanuts.

——Eat less brown-baked biscuits, cookies, pastries, steamed buns and other snacks.

——Eat less potato chips, rice crusts and other fried or oil-baked foods.

On the other hand, AGEs are also produced during long-term storage. For example, although cheese is not heated at high temperatures and most of the lactose is removed during production, it undergoes a long fermentation period of several months. During this process, some fats and proteins are gradually decomposed, and the active carbonyl compounds produced by the oxidation of fats and proteins react with the amines produced by the degradation of amino acids, which will also accumulate the products of the Maillard reaction and increase the number of AGEs[8].

Foods that have been preserved for a long time, such as sausages, bacon, dried fish, and dried meat, all show a similar pattern: the AGEs content increases during storage. Adding a large amount of salt to preserve food will accelerate this process[9].

Many friends may ask: So, are there any foods that can reduce or eliminate AGEs in food? Yes, there are.

The second way to reduce AGEs is to ensure the ratio of vegetables, fruits and whole grains, and to consume appropriate amounts of sour condiments and natural spices to reduce the amount of AGEs produced in the body.

Acidic substances such as lemon juice and vinegar have similar effects . Studies have reported that spices such as tea, pomegranate peel, garlic, and polyphenol extracts from some fruits, vegetables, and herbs can help reduce glycation reactions, thereby reducing the production of AGEs during food cooking and processing[9].

Eating more fresh fruits and vegetables, whole grains and beans in daily diet and achieving food diversification can help reduce the intake of AGEs in the diet and provide a variety of food ingredients that inhibit the formation of AGEs. At the same time, a healthy diet itself is conducive to improving blood sugar and blood lipid levels, thereby reducing the amount of endogenous AGEs formed.

The last thing to say is:

Any substance in food follows the rule of "dose determines toxicity". Foods containing AGEs are not poisons, just like foods containing sugar and salt. They provide deliciousness and are good for appetite. At the same time, the body's inflammatory response is not the lower the better. Therefore, enjoying delicious food heated at high temperatures appropriately is part of a happy life .

However, everything should be done in moderation, including delicious food . Frequent grilling, frying every day, and eating a lot of grilled food are not healthy eating habits. In addition to a large number of AGEs that promote aging, more pro-inflammatory substances and even carcinogens will be introduced.

References:

1 Fan W, Adebowale K, Váncza L, et al. Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver. Nature, Jan 31, 2024

2 JA Lin, CH Wu, GC Yen. A perspective of advanced glycation endproducts (AGEs) on human health. Journal of Agricultural & Food Chemistry, 2018, 66(9): 2065-2070

3 Advanced glycation end products via skin autofluorescence as a new biomarker for major adverse cardiovascular events: A meta-analysis of