Sudden Turns of Thought: Rapid-Fire Q&A (Part 2)

Hi everyone, welcome to Cold-Knowledge Blind Box. I'm your community host, Qiao Yulan. Have you ever come across an ordinary phenomenon or idea in everyday life, but when you think about it hard, you can't figure out why it exists? For example, why is the smell of grilled meat on a cold winter day so irresistible? What's the chemistry behind it? And when you've eaten too much, you often feel your body is weighed down. How can you eat and drink in a healthy, scientific way?

Beyond calories, how does insulin affect modern life?

How many people, like me, on a freezing winter day, walking past a barbecue restaurant, have their soul carried off by the aroma of the grilled meat even while their feet are still on the sidewalk? Heavens, why does grilled meat smell so good? From a scientific point of view, grilled meat and toast smell good because the food undergoes the Maillard reaction while it's being heated.

When amino acids (an important component of meat and protein) are heated together with carbohydrates, which are the sugars or starches we know well, the mixture changes color from the raw red of meat to a deep brown, producing a whole range of complex flavors and aromas. Many chemical reactions happen during this process, such as the reduction of sugars and the deamination and rearrangement of amino acids.

"The Maillard reaction" sounds like a person's name. But can you publish a scientific paper while eating grilled meat? Actually, yes, you can!

The first person to notice this phenomenon and write it up in a scientific journal was a French biochemist named Louis-Camille Maillard, whose day job was researching the artificial synthesis of proteins.

In 1912, in an experiment simulating biochemical reactions inside the human body, he heated a solution of amino acids with sugars and found that the mixture gradually darkened and produced a distinctive aroma. He published a paper describing the process in 1913, but he didn't pursue further research. After all, in that era of war, when people were just glad to have enough to eat, who had the time to figure out how to make food tastier?

It wasn't until 1953, after World War II ended, that a chemist named Hodge, working at a U.S. Department of Agriculture laboratory, filled in the reaction mechanism from Maillard's paper, that is, the chemical equations. With peace came a new era. People no longer aimed merely to fill their stomachs but were willing to spend money on better food at home.

This sent the food industry racing forward. Entrepreneurs were eager to know how to make, faster and in greater quantities, the secret of delicious food that would please most consumers. Relying only on the traditional, hand-me-down recipes of a few chefs in a kitchen could never make that possible.

The Maillard reaction, written up in scientific journals, provided a theoretical foundation that made mass, assembly-line production of deliciousness possible. After all, it amounted to directly mastering the code for pleasing human taste buds. Anywhere food is processed through heating or roasting, such as roasting coffee beans, baking bread, or turning cacao beans into chocolate, making good use of the Maillard reaction helps the food come out just right.

By the way, Maillard-inspired fashion colors are also among this autumn and winter's trends. Compared with the black, white and gray coats common in winter, the deep reds, yellow-browns and caramel shades of the Maillard palette feel warm, like delicious food.

Still, grilled meat, cake and milk tea are wonderful, but a sensible little voice inside us always reminds us to stop eating, or we'll gain ten jin (about 11 pounds) this winter!

So let's dig a little deeper. What exactly causes weight gain? That's an easy one, isn't it: calories. Eat more and move less, and of course you get fat. Yes, the calorie model is practically common knowledge. The catch is that its history goes back to the 19th century, to the period when nutrition research was happening alongside the formulation of the law of conservation of energy.

The core of the calorie model is the balance between energy intake and energy expenditure. It seems that as long as you follow this formula and satisfy it, your body definitely won't get fat, or will gain weight successfully. If you control your diet and exercise, you can supposedly reach any ideal weight. But in reality, we all know that changing your weight in the short term is very difficult, and there are always some people who can eat whatever they like and never gain weight. So where does the model go wrong?

In 1944, a starvation experiment conducted at the University of Minnesota gave us the answer: the calorie model is flawed, because the human body contains an independent energy-balance system, and you can't look at intake and expenditure as static quantities.

At that time, World War II was drawing to a close. Many refugees in Europe were starving. The U.S. government wanted to understand the long-term effects of hunger on the human body, in order to provide scientific guidance for postwar nutrition aid and rehabilitation programs. But there were no starving refugees in the American homeland, so the government funded the University of Minnesota to carry out this starvation experiment, which looks very inhumane by today's standards.

The scientists recruited 36 male volunteers and followed them for a year. For the first three months, the subjects were asked to consume 3,200 calories a day (roughly the equivalent of eleven steamed buns with meat filling). Then, during a six-month starvation period, they took in only 1,570 calories (about five steamed buns a day). Finally, for the last three months, they went back to eating 2,000 to 3,200 calories.

The scientists took out pencil and paper to calculate. These subjects should, on average, have lost 35.3 kilograms during the starvation period. But in reality, they lost only 16.8 kilograms. Even more alarming, nearly everyone developed a drop in body temperature, weakened strength, extreme irritability and depression during the starvation period. And in the three months after eating resumed, many subjects binged, and their weight and body fat rose above their levels before the experiment.

That shouldn't have happened. The scientists had tightly controlled the variables in the experiment, and if the law of conservation of energy held, this outcome shouldn't have occurred. The scientists weren't satisfied, and after further research they discovered the flaw in the calorie model itself. Intake and expenditure can't be calculated separately, because every person has a built-in balance system.

When intake decreases, expenditure and metabolism naturally decrease as well, until a new balance is formed. When dieting is suddenly interrupted, and the body takes in far more than before while expenditure and metabolism remain at a low level, weight shoots up like a rocket.

That's why so many people find weight loss so hard. When they finally succeed, the weight springs back in an instant. This is because, without changing the overall balance, the body is desperately trying to make up for the balance it had before.

Finding flaws in an old theory is only the first step toward a new one. In 1993, in an insulin experiment, researchers gave four groups of diabetic patients different doses of insulin, and in one group they reduced the calorie intake. The result: the weight of this group didn't fall at all. Instead, it kept rising along with the insulin dose.

Could the key to body weight be insulin rather than calories? There is evidence for this idea. For example, before artificial insulin was invented, people with type 1 diabetes, whose bodies produced very little insulin, could not gain weight no matter how much they ate.

But how is insulin connected to weight? That brings us to how insulin works. When we start eating, the small intestine absorbs many nutrients and breaks them down into glucose. The pancreas then secretes a large amount of insulin. Insulin itself is a hormone, and it helps cells break down glucose in the blood.

Imagine that the body's energy storage works like putting food into a small refrigerator and a large freezer. Insulin is responsible for storing energy in the small refrigerator, which is used often, by forming glycogen. When the small refrigerator is nearly full, insulin stores the surplus energy in the large freezer, by forming fat.

Under normal circumstances, when you stop eating for a while, the body first breaks down glycogen from the small refrigerator for energy. When the small refrigerator is empty, it burns fat from the large freezer for fuel. This is a very healthy process. In theory, burning fat is more efficient, and people would certainly rather see fat being used. Wouldn't that make you slimmer?

But if your pancreas keeps secreting insulin (in other words, your cells have developed insulin resistance, so more insulin-producing cells are needed to help cells consume blood sugar), and your body has become accustomed to high levels of insulin, another situation arises. Excess insulin is itself a signal, and it says that blood sugar is already plentiful, so there's no need to burn fat for energy. This is like stopping the body from burning fat to get energy. When you can't get energy, you feel very hungry, and when it becomes unbearable, you eat again. Now, more insulin arrives, and your fat becomes even harder to burn.

This is the new model proposed by modern nutrition science, also known as the carbohydrate-insulin model, or CIM for short.

So based on this theory, the advice for not gaining weight in winter is actually very simple: let your pancreas rest a bit, slow down insulin secretion, and don't let it work "996" (the infamous overtime schedule of Chinese tech culture). Lengthen the intervals between meals, and cut back on high-carbohydrate foods like rice and noodles.

Through these two theories, we can clearly see that the human body is an extraordinarily complex system, and every person has individual differences. Blaming obesity simply on eating is far too simplistic. Metabolism, hormone regulation, genetics, the gut microbiome, and other biological and environmental factors all play important roles in the processes of energy intake, storage and expenditure.

I really like one saying: every person is a tiny universe, and the countless cells and microorganisms living inside our bodies have a balanced ecosystem of their own.

That's the end of today's rapid-fire Q&A on knowledge. If there's anything else you'd like to hear, you can also open the NIO app, go to the Friends tab and the community section, and find the NIO Radio Shenzhen City Station. Let's share the cold knowledge you love together!

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