Excerpt from Why We Get Fat
In the book Why We Get Fat, I found a more detailed principle to explain how we get fat. For a fat man who is troubled by obesity, it is meaningful for me to master this principle.
The original text is all words, and the logical relationship inside is very complicated. I made a special brain map, which roughly straightened out these complicated relationships.
Share the brain map and attach the original text to make it easier for everyone to understand this complex principle.
Original text:
It's time to roll up your sleeves and start solving the obesity problem. What we need to know is: What are the physiological factors that regulate the amount of fat in tissues? Specifically, it is necessary to know how your diet affects this adjustment, so that you can know what you did wrong and how to correct it. We also need to know what determines the "essence" of getting fat or staying slim, and what nutrients, diet and lifestyle can be used to change this tendency and fight obesity.
I'll talk about basic physiology and endocrinology first. Understandably, you will find these topics difficult to understand. What I can guarantee is that if you put your heart into it, you will eventually learn everything you should know-why people get fat and how we should solve it.
A simple question: Why store fat?
Okay, I'll explain. Some fats in the human body provide insulation to keep us warm; Others guard the periphery of organs to protect more fragile internal organs; So what's the use of the remaining fat? Like the fat around the waist?
Usually, experts think that fat storage is like a long-term savings account-a pension account that will only be used when it is urgently needed. This means that you consume extra calories and hide them in the form of fat. These fats will remain in adipose tissue until one day, your body finds that you are not full (dieting, exercising, or being trapped on a desert island), and you will use these fats as emergency fuel.
Fat continuously flows out of fat cells and circulates in the body as fuel. If it is not burned by other tissues as fuel, fat will return to fat cells. Whether we eat or exercise recently, this cycle continues. 1948, Ernst Wertheimer, a German biochemist who immigrated to Israel and can be said to be the father of fat metabolism research, wrote: "The transfer and deposition of fat alternate constantly, which has nothing to do with the nutritional status of animals."
The phrase "has nothing to do with the nutritional status of animals" is often quoted in academic discussions on adipose tissue regulation. This means that even if people or other animals don't consume as many calories as they do-as Jean Mayer said, they are "semi-hungry"-they will still store calories as fat. As I pointed out before, this sentence alone can explain why there are obese mothers and starving children in poor societies.
In 24 hours a day, most fat cells are used as fuel for cell combustion to obtain energy. Nutritionists may think (and like to tell us so) that sugar is the first choice fuel for the body in a certain way. Because cells burn sugar before burning fat (unfortunately this is a low-level misleading). The cause and effect of this is that if your diet is rich in sugar (as most people do), your cells will burn a lot of sugar before burning fat.
Imagine that you are eating. Like most meals, this meal contains both sugar and fat. After the fat is digested, it is directly sent to fat cells for storage. For sugar, the body needs a more direct role. After sugar is digested, it appears in the blood in the form of glucose, which is the "sugar" in blood sugar. Cells in the whole body consume glucose in the blood as fuel. However, unless cells are helped by other partners in the body, they cannot directly capture and consume glucose by themselves.
This help partner is insulin. Insulin has many functions in the body, but the most important function is to control blood sugar. Before you start eating, the pancreas starts to secrete insulin. In fact, as long as you want to eat, your pancreas will be stimulated by the brain. This reflex can also occur without conscious thinking. In fact, insulin is physically prepared for you to eat. When you take the first bite, you will secrete more insulin. As glucose in the diet begins to enter the blood circulation, more insulin is secreted.
Then, insulin sends a signal to cells all over the body to speed up the "uptake" of glucose from the blood. These cells will use part of the glucose they ingest as direct energy, and the other part will be stored as spare. Muscle cells store glucose in the form of molecules called myoglycogen, while liver cells store some glucose in the form of hepatic glycogen, while others are converted into fat. Fat cells certainly store glucose as fat.
When your blood sugar begins to drop, so does your insulin level. More and more fat stored during meals is released from adipose tissue, occupying the vacant energy part of your blood. The longer the time passes after a meal, the more fat you burn (the more you release) and the less glucose you consume. The reason why you can have a good sleep is that you don't have to get up every few hours to open the refrigerator to find food, because the fat flowing out of adipose tissue can ensure that all tissues and cells can work normally until tomorrow when you don't eat breakfast.
Therefore, perhaps adipose tissue is more like a wallet than a savings card or pension account. You keep putting fat in and taking it out. During or after each meal, you will gain a little weight (more fat enters fat cells than comes out), and then you will lose a little weight after the meal is digested (the opposite happens). Stay slim when you sleep. In an ideal country that won't get fat at all, the fat stored after eating during the day is released at night and consumed when not eating.
Fat cells are like an energy buffer, which provides a place to store the heat you absorb during meals but don't use it immediately. When you need calories, fat cells will put them back into the blood circulation. It's like your wallet provides you with such a place to store the money withdrawn from the ATM, which you can use all day. Only when the fat reserve drops to the lowest point will you feel hungry again and have the motivation to eat again. Just like we like to set a minimum cash limit in our wallet, when the cash is less than this point, we will go to the ATM to "recharge".
However, although fat goes in and out of our fat cells all day, this fact does not explain clearly how the cells decide which fat goes in, which fat comes out and which fat has no choice but to be locked in the cells. The cell's decision is simple: look at the size of fat.
The fat in our body exists in two different forms and has completely different purposes. The fat that can get in and out of cells is called fatty acid, and we burn this form of fat as fuel. The fat that must be stored is called triglyceride, which is composed of three fatty acids connected by glycerol.
The reason for this role assignment is super simple: triglycerides are too big to cross the cell membrane around fat cells, while fatty acids are too small to slip through the cell membrane relatively easily. Fatty acids go in and out of cells all day, and once needed, they are burned as fuel. Triglycerides are hidden for a rainy day.
When fatty acid enters fat cells, it will connect with one glycerol molecule and two other fatty acids to form a brand-new triglyceride. So it became bigger, and now it can't go out freely through the cell membrane. So now these three fatty acids are trapped inside the fat cells, and they can't flow out of the cells again and return to the blood circulation before the triglycerides are decomposed or destroyed. For example, people who buy large pieces of furniture find that the furniture is too big to get in. You must break the furniture into small parts, then move the parts into the door and put them back. If you want to move a particular piece of furniture to your new home, you must open it in the house, put it together outside, and then repeat the process.
Therefore, anything that promotes the flow of fatty acids into fat cells and links them with triglycerides will help store fat and eventually make you fat. Substances that can break down these triglycerides into fatty acid molecules and make fatty acids escape from fat cells will help you lose weight.
It's actually quite simple. As Edwin Astwood pointed out half a century ago, dozens of hormones and enzymes play a role in these processes, and it is easy to speculate how they are disturbed, so that too much fat comes in and too little goes out.
However, only one hormone dominates this activity, and that is insulin. 50 years ago, Astwood pointed out this point, which has not caused controversy so far. As I said, the insulin you secrete first reacts to the sugar in your diet. The main purpose of this is to control blood sugar. However, insulin is also responsible for coordinating the storage and utilization of fat and protein. For example, it can ensure that your muscle cells get enough protein for necessary reconstruction and repair, and it can also ensure that you store enough fuel (glucose, fat and protein) between meals to function normally. The place where we store spare fuel is adipose tissue, and insulin is the main regulator of fat metabolism. This was discovered in 1965 by two scientists, Solomon Belson and Rosalyn Yarrow. They invented the key technology of measuring blood hormone levels. Because of this work, Arrow later won the Nobel Prize. Of course, Bertrand could share the honor, but unfortunately he died before the award was given.
Insulin does this mainly through two enzymes. The first is lipoprotein lipase, which is usually referred to as LPL for short. I mentioned this enzyme before when I was talking about how mice get fat after ovariectomy. LPL is an enzyme detected from cell membranes of different cells. It extracts fat from blood and puts it into cells.
If LPL is on the surface of muscle cells, it pulls fat into muscle and uses it as fuel. If it is on the surface of fat cells, it will make the fat content of fat cells higher. As I said before, female estrogen inhibits the activity of LPL on fat cells, so there is less fat accumulation.
LPL simply answered many questions I asked about the location and time of obesity. Why do men and women get fat in different ways? Because of the different distribution of LPL, it is also affected by LPL sex hormones.
LPL activity in adipose tissue of male viscera is relatively high, so it is easier for male viscera to obtain fat, while LPL activity in adipose tissue below waist is relatively low. With the increase of men's age, one of the reasons for getting fat above the waist is that they secrete less testosterone (an androgen), but testosterone can inhibit the LPL activity of abdominal fat cells. The less testosterone, the stronger LPL activity on visceral adipocytes, so the more fat.
LPL activity in fat cells below the waist of women is relatively high, while the activity in visceral fat cells is relatively low, which is the reason why their hips are easy to get fat. After menopause, the LPL activity of women's abdominal fat catches up with that of men, so they also tend to accumulate excess fat at the waist. When a woman is pregnant, LPL activity in the buttocks increases, and heat is stored there to meet the needs of raising babies in the future. Storing fat below the waist and buttocks can also balance the weight of the fetus growing in the uterus. After giving birth to a child, LPL activity below the waist decreases, and the excess fat obtained before disappears, at least most of the fat disappears; However, LPL activity in breasts and breasts has increased, enabling women to use these fats to produce milk to feed their babies.
LPL is just the best answer to the question "Why don't we lose fat during exercise?". We already know that LPL activity in adipocytes is slightly lower than that in muscle cells. This will promote adipose tissue to release fat, so that we can burn these fats in muscle cells that need fuel, and we will be thinner. So far, so good. But when we exercise, the situation will reverse. At this time, LPL activity on muscle cells is weakened, while LPL activity on fat cells is rapidly increased, and fat cells begin to re-store any fat reduced during exercise. We are getting fat again. This also explains why exercise makes us hungry. Not only do our muscles need protein to recover and rebuild after exercise, but our fat should also be actively re-stored. The rest of the body always tries to compensate for this loss of energy, so our appetite increases.
Since insulin is the main regulator of fat metabolism, it is not surprising that it is also the main regulator of LPL activity. Insulin activates LPL on adipocytes, especially abdominal adipocytes, thus "up-regulating" LPL. The more insulin we secrete, the higher the LPL activity of fat cells, and the more fat we transfer from blood to fat cells for storage. Insulin can also inhibit LPL activity on muscle cells to ensure that muscle cells do not have many fatty acids to burn. Insulin will also "tell" muscle cells and other cells in the body not to burn fatty acids, but to continue to burn blood sugar, so as to ensure that the blood sugar level will not be too high. This means that when fatty acids escape from fat cells, if insulin happens to be at a high level, these fatty acids will not be absorbed by muscle cells and used as fuel. These fatty acids will eventually return to adipose tissue.
Insulin can also affect an enzyme that we have not discussed-hormone-sensitive lipase, which is usually referred to as HSL for short. This enzyme may be crucial when discussing how insulin regulates the amount of fat we store. Just as the function of LPL is to make fat cells (and us) fat, the function of HSL can make fat cells (and us) thin. It can do this mainly because it has the ability to decompose triglycerides in fat cells into fatty acid molecules. In this way, these fatty acids can enter the blood circulation and be consumed. The more active HSL is in the human body, the more combustible fat we release and the less fat we store. Insulin can not only increase LPL activity, but also inhibit HSL activity.
Only a little insulin is needed to complete the feat of reducing HSL, and a lot of fat is trapped in fat cells. When the insulin level increases, even a little, fat will accumulate in fat cells and cannot be excreted.
Insulin can also start a new skill in fat cells-let them inhale glucose, thus increasing the amount of glucose metabolized by fat cells. So is insulin in muscle cells. There is more glucose in fat cells, and glucose metabolism is more vigorous, but one of the products of glucose metabolism is glycerol. At this time, these newly added glycerol molecules can synthesize triglycerides with fatty acids, and fat cells store more fat.
In order to ensure that we have enough space to store all the fat, insulin has another function: in case our existing fat cells are full, insulin can give instructions to create new fat cells. Insulin also signals liver cells not to burn fatty acids, but to reassemble them into triglycerides and send them back to adipose tissue.
In short, all insulin does in this situation is to increase the fat we store and reduce the fat we burn.
It can also be said that the role of insulin will make us fat. This happens when our whole body's insulin level rises.
This is why diabetics usually gain weight when receiving insulin therapy. Joslin's Diabetes Mellitus, an authoritative journal of diabetes, clearly wrote that obesity is caused by "the direct effect of insulin on obese tissues". In 2008, a research report in the New England Journal of Medicine pointed out that patients with type 2 diabetes gained an average weight of 3.6 kilograms after receiving intensive insulin therapy. Almost one-third of diabetics gained 9 kilograms in three and a half years.
Because the level of insulin in blood mainly depends on the intake of sugar, it is these sugars that ultimately determine the amount of fat we accumulate. The following is a chain reaction of a series of events.
1. You want to eat a sugary meal.
2. You start to secrete insulin.
3.？ Insulin signals fat cells to stop releasing fatty acids (through HSL) and begin to absorb more fatty acids from the blood circulation (through LPL).
4. You feel hungry, or become more hungry.
5. You start eating.
6. You secrete more insulin.
7. After being digested, sugar enters the blood circulation in the form of glucose, which leads to an increase in blood sugar content.
8. You secrete more insulin.
9.？ Fat in food is stored in fat cells in the form of triglycerides, and some sugar is converted into fat in the liver.
10. Fat cells get fat, and so do you.
1 1. Fat will remain in fat cells until the insulin level drops.
If you doubt whether there are other hormones that make us fat, the answer is: no, with a few obvious exceptions. Acylation promoting protein, a hormone discovered in the late 1980s, is probably an exception, but it is secreted by adipose tissue itself, and some processes are regulated by insulin.
One view of the role of hormones is that they command the body to do certain things-growth and development (growth hormone), reproduction (sex hormone), flight or fight (adrenaline). They also provide usable fuel for these different activities. Besides, they have other jobs. They send signals to adipose tissue to mobilize fatty acids to provide usable fuel.
For example, we secrete adrenaline to deal with the threats we face. Adrenaline prepares us to run or fight. However, if a lion rushes at you in front of you, you know you have to run away, but you lack emergency fuel and can't run faster or farther than the lion (maybe both), so the lion will catch you. Therefore, when you see a lion, you will secrete adrenaline; Adrenaline, which may be busy with other things, immediately sends a signal to adipose tissue, asking them to transport fatty acids into the blood circulation as soon as possible. Ideally, these fatty acids will provide all the fuel you need to escape. In this sense, all hormones except insulin can cause adipose tissue to release fat. They make us thin, at least temporarily.
However, if the insulin in the blood circulation is at a high level, it will be difficult for other hormones to release fat from adipose tissue. The effect of insulin is far greater than that of other hormones, which is very necessary. Because if there is a lot of insulin around, it means there should be a lot of sugar around to burn, which means the blood sugar content is high. In this way, we don't need or want fatty acids that get in the way. Therefore, only when insulin is at a low level can other hormones release fat from adipose tissue. Other hormones break down triglycerides by stimulating HSL, but HSL is very sensitive to insulin, and other hormones cannot overcome this characteristic.
The hormone cortisol is a special exception. This is a hormone that we secrete when dealing with mental stress or anxiety. The real function of cortisol is to put fat into adipose tissue and then take it out. It stimulates LPL (lipoprotein lipase) to put in fat, just like insulin; At the same time, it also triggers or intensifies the so-called "insulin resistance" to put on fat, which I will elaborate in the next chapter. When you are resistant to insulin, your body has to secrete more insulin and store more fat.
Therefore, cortisol allows us to store fat directly (through LPL) and indirectly (through insulin). But then, like other hormones, it mainly stimulates HSL to release fat from adipocytes. Therefore, when insulin is at a high level, cortisol will make us fat together with insulin; But when insulin levels are low, cortisol, together with all other hormones, makes us thin. This may explain why some people get fat when they are nervous, anxious or depressed and overeating, while others do the opposite.
For more than 40 years, we have been engaged in such metabolic research. We now know that if we want to be thin, we must extract fat from adipose tissue and burn it-one thing we must do is to lower our insulin level. If we can keep the insulin level at a reasonably low level, we can burn fat. If we can't lower the insulin level, we can't burn fat.
When we secrete insulin, or the insulin content in the blood is abnormally high, fat will accumulate in adipose tissue, so we will gain weight. This is what science tells us.
Where does fat come from, where does it go, and what hormones are regulating it? We have got the general situation. During the day, when we digest food, we will get fat, because the intake of sugar increases the insulin level; We consume fat until the next meal and go to bed at night. Ideally, the fat obtained in the fat storage stage can be balanced with the fat consumed in the fat burning stage. The fat we get during the day burns at night, and insulin fundamentally controls this cycle. As I said, when insulin levels increase, we store fat; When insulin drops, we use fat as fuel.
This shows that any factors that make us secrete more insulin than normal or keep high insulin content for a longer time than normal will prolong the fat storage cycle and shorten the fat burning cycle. Within a few hours after a meal, as the blood sugar content drops to the level of the pre-meal stage, we rely on fatty acids as fuel.
However, insulin inhibits the outflow of fatty acids from fat cells, which tell other cells in the body to burn sugar first. Therefore, if the insulin level remains high, we will have no available fat as fuel. We couldn't use the sugar stored in liver and muscle tissue before, because insulin also locked them up.
As a result, cells find themselves seriously short of fuel, and we can really feel their dilemma: hunger. We either eat earlier than usual, or eat more than usual, or both. That's it. Anything that makes us fat will make us eat more, which is the result of insulin.
At the same time, because we store more fat, our bodies will become huge, which will further increase our demand for fuel. Therefore, our appetite will also increase-especially sugar, which is the only nutrient that our cells can burn as fuel when the insulin content is high. This is a vicious circle, and we should try our best to avoid it. Please remember carefully that when we tend to get fat, we are driven by our bodies to look for food rich in sugar, right?