The body’s response to caffeine 

Nowadays, people are often in a work environment with high pressure and the pursuit of high efficiency. Coffee has become one of the indispensable drinks for many people, not only because of its aroma and taste but also because coffee has a great refreshing effect on many people. The key ingredient is caffeine. 

What is caffeine? 

Caffeine is a central nervous system stimulant that stimulates the sympathetic nervous system to achieve the effect of refreshing the mind, improving concentration, and combating fatigue. In terms of exercise, whether it is aerobic exercise (to increase endurance) or anaerobic exercise (to increase. Some literature also points out that caffeine can effectively increase basal metabolic rate. 

The effective dose of caffeine for each person will vary depending on their body type and tolerance, which is why some people will be unable to sleep all night after drinking just a small amount, while others can still sleep. 

The human body has obvious physiological reactions to caffeine, such as: 

anxiety (some people become anxious) 

blood pressure rises 

promotes gastrointestinal motility 

promotes gastric acid secretion 

diuretic 

Explain the benefits of coffee for the body.  

Help with fat loss? 

Many people have probably heard the claim that “drinking coffee helps burn fat.” There is some scientific evidence for this. 

One study found that the caffeine group had nearly twice the lipid turnover, an increase in free fatty acids in the blood (increased breakdown), and a better thermogenic effect than the placebo group. Energy expenditure was also about 13% higher than the placebo group. However, at the end of the article, the author also mentioned that only 24% of the lipids were oxidized, while 76% were recycled and stored again in fat cells. Cells. In layman's terms, drinking coffee may slightly improve your body's ability to metabolize fat, but if you still don't give your body the so-called energy-consuming demand, that is, exercise, it will not help you lose fat. 

Research source: https://www.ncbi.nlm.nih.gov/pubmed/14684395 

Enhance autophagy? 

In addition, caffeine has been mentioned in past studies as being able to enhance “autophagy.” What is autophagy? 

Simply put, the body renews cells in the body through autophagy and eliminates old cells in the body through autophagy to achieve a mechanism for renewing cells in the body. Autophagy is particularly active when fasting is performed. Since the body is challenged, it must activate survival mode and use autophagy to break down body tissue to provide energy, including body fat, of course. 

Source: https://www.ncbi.nlm.nih.gov/pubmed/28949381 

Boosts satiety? 

Caffeine can boost satiety and suppress hunger. The mechanism of autophagy is controversial. One school of thought believes that caffeine can stimulate the sympathetic nervous system to suppress appetite. A study was conducted to test this theory by simulating the most common coffee consumption pattern: “a cup of coffee in the morning. 

The results showed that the group that drank coffee had about 10% less energy intake at breakfast than the control group, but there was not much difference in energy intake at subsequent meals, and there was no significant difference in the feeling of appetite between the two groups Difference: “In theory,” caffeine suppresses the secretion of hormones by the glands in the digestive tract by stimulating the sympathetic nerve, which of course also includes the secretion of gastric hunger hormone by the stomach. However, judging from the statistics, it can be explained that there are individual differences in the physiological response of each person to caffeine. 

Research source: https://www.ncbi.nlm.nih.gov/pubmed/300331 

Caffeine is a substance that can very effectively stimulate the sympathetic nervous system, which in turn increases the body's production of adrenaline. 
Adrenaline can make us feel focused, improve training results and suppress hunger, but in the long term it is not necessarily a good thing. There is no direct experimental evidence to prove the existence of the so-called “adrenal fatigue,” but there are many physiological characteristics that “may” be associated with excessive adrenal hormone secretion. 
Symptoms of adrenal fatigue include: 
Fatigue Introduction to the disadvantages of caffeine for the body - adrenal fatigue 
Poor sleep, inability to get up 
Unexpected significant weight loss 
Caffeine dependence 
Abnormal digestive problems 
These symptoms may indicate that you are under a relatively high level of physical or psychological stress, which overstimulates the adrenal cortex to secrete stress hormones. 
The side effects of high stress on fat loss 
High stress has always had a great impact on fat loss. When the body is in a state of high stress for a long time, the adrenal glands secrete “cortisol,” a stress hormone that keeps blood sugar at a peak. High blood sugar also means high insulin resistance, and cortisol also has the effect of breaking down muscle, which is very undesirable during the fat-loss period. A study divided the subjects into a placebo group (who did not consume coffee on weekdays) and a caffeine group (who consumed 300 mg of caffeine per day), and on the day of the experiment, they were given placebo & caffeine capsules respectively, and then all of them were given a stress test, and their cortisol was immediately tested after the end. It was found that the group that had a habit of drinking coffee on weekdays had higher cortisol levels after the stress test than the placebo group, and the subsequent decline was also slower. Higher cortisol levels also indicate higher blood sugar and insulin resistance, which is not a good sign for weight loss and fat loss. 
Research source: https://www.ncbi.nlm.nih.gov/pubmed/16631247 
Natural metabolism Caffeine has problems. 
The metabolism of caffeine is affected by many factors, including age, gender, diet, lifestyle, and external environmental factors. 
Age: 
In newborns, the caffeine metabolism function is the worst in their lives. 
Because the liver is the main organ for metabolizing caffeine, and the liver function is not yet mature at this time, with age, the caffeine metabolism ability will gradually increase. Therefore, since the enzyme responsible for metabolizing caffeine is secreted by the liver, it is not recommended for people with congenital or acquired liver diseases to consume too much caffeine. 

Gender and pregnancy: 
In terms of gender, men have slightly more active enzymes for metabolizing caffeine than women, but there is no statistically significant difference. As for pregnant women, some people may have heard that excessive caffeine intake may increase the risk of miscarriage. 
However, unlike alcohol, caffeine has been confirmed to affect the development of the baby, so drinking it once or twice a week will not have a significant impact. 
Diet: 
An interesting study has shown that formula-fed babies have a better ability to metabolize caffeine than breastfed babies. The enzyme CYP1A2, which is responsible for metabolizing caffeine, is stimulated by substances in cow's milk and becomes more active. This may explain why we feel more awake after drinking black coffee than after drinking a latte. However, does regular coffee consumption increase the rate of caffeine metabolism? This argument has been controversial in past studies, so the metabolic perspective may not be suitable for explaining the phenomenon of “coffee becoming less effective the more you drink.” It may be more appropriate to explain this using the adrenal fatigue just mentioned. 
Research source: https://www.ncbi.nlm.nih.gov/pubmed/2951487 

Who shouldn't drink coffee (or caffeinated drinks)? 

People with liver disease 

As mentioned earlier in the video, the liver is mainly responsible for metabolizing caffeine, so people with liver disease may need longer to metabolize the caffeine in their bodies. 

People with digestive system diseases (especially stomach) 

The tannins in coffee can stimulate the secretion of gastric acid, which may make you feel even more uncomfortable if you already have a stomach problem. Even if you have recovered, it is recommended not to drink caffeinated drinks on an empty stomach. 

People with cardiovascular disease 

Caffeine has the function of stimulating the sympathetic nerve to accelerate the heartbeat and promote vasoconstriction. Excessive caffeine can cause palpitations, which is a risk for people with cardiovascular disease. 

Pregnant women 

Whatever the mother eats or drinks will also be supplied to the baby in the womb. However, the fetus cannot metabolize caffeine until the eighth or ninth month, so it is also not recommended for pregnant women to consume caffeinated drinks every day. 

High stress 

Caffeine can cause fatigue by constantly stimulating the sympathetic nervous system. The above-mentioned symptoms of adrenal fatigue will only make people under high stress feel more and more tired. 

Fat loss stagnation 

Long-term consumption of caffeinated drinks, even zero-calorie drinks like black coffee, is a hidden killer that can cause weight loss to stall. It is not difficult to discover from a physiological perspective that caffeine does indeed keep blood sugar and insulin resistance at a peak in the body by constantly stimulating the adrenal glands to secrete the stress hormone cortisol. This is the opposite of what is emphasized during the weight-loss period: “stabilizing blood sugar, reducing insulin resistance, and improving insulin sensitivity.”