《油脂對肥胖的關係不大》

（與Brucc A等先生商榷)

黃學章（2021/11/8）

Brucc A等先生在由其編寫的《貝雷，油脂化學與工藝學》第七章，第四節中寫道：

“儘管人們對肥胖的原因理解疑問重重，但仍有證據顯示，造成肥胖的慢性能量代謝不平衡大部分由脂肪的熱量引起（4.1引言)”。

“飲食中脂肪的飽腹感差，會有選擇地引起肥胖。與碳水化合物，蛋白質，酒精不同，人體對於脂肪的氧化代謝調控較差。飲食中增加的脂肪不會加速它自身的氧化，而是促進多餘的脂肪向脂肪組織中的儲存。

所以脂肪是造成長期能量正平衡，與肥胖相關的主要飲食因素。（4.7結論)”。

上述文字的意思是，肥胖是由於過度攝入脂肪引起，理由是：

1，因為脂肪的飽腹感差，可能誤以為還沒吃飽，而過度飲食，導致肥胖。

2，脂肪攝入過量，多餘的脂肪不能被氧化消耗掉，被儲存到脂肪組織中，導致肥胖。

3，人體對脂肪氧化代謝的調控能力比碳水化合物，蛋白質差。因此，人體生理活動所需要的能量，優先從糖和蛋白質氧化代謝獲取，而脂肪的氧化代謝則被滯後，忽視，從而導致脂肪積累形成肥胖。

然而，這些論斷是值得商榷的。

1，脂肪的飽腹感差，並不一定導致過度飲食，這只是個飲食習慣問題而已。

2，從外部攝入的動植物脂肪，是不能直接儲存起來的。人體儲存的，必須是自己合成的各自獨特的脂肪。

正如德國哲學家萊布尼茨所說:“世上沒有兩片完全相同的樹葉”。每個人的脂肪結構特點也都不會完全相同，更不可能直接儲存動植物脂肪。

3，脂肪與糖（澱粉)和蛋白質的氧化代謝途徑基本上是一致的。都是先轉化為乙酰輔酶A，再通過“三羧酸循環”，徹底氧化為二氧化碳和水，並放出能量。

油脂含有羧基和雙鍵活性基團，氧化代謝的速度和“可控性”，應該高於糖類和蛋白質，而不是低於……。

所以，人體在體力腦力活動時，所需的能量，優先是來自於脂肪的氧化代謝，其次才是來自糖和蛋白質。

否則，如果是優先消耗糖，蛋白質，後消耗脂肪，那麼健美運動員去掉的將是肌肉，留下的是脂肪，也就不可能有健美運動了。同樣，通過運動減肥也就無法成功。

本人4年多來，每天早晨空腹喝40毫升植物油，的確沒有飽腹感，然後連續，快速步行近一個小時，體力依然充沛，還未感到飢餓。這說明脂肪既能快速消化吸收，又能快速氧化代謝釋放能量。

因此一座可調控的，收支靈活的，能量效率高的脂肪庫，才是人體所必須的。

而肥胖，則是由於攝入碳水化合物、蛋白質、動植物脂肪等營養物質總量過剩而造成。

多餘的營養物質經過消化吸收，再在肝臟或腸壁內，合成為人體脂肪儲存起來。只要總攝入量有所控制，人體脂肪儲存不致過量，就不會引起肥胖。

在人體脂肪的合成過程中，碳水化合物、蛋白質以及動植物油脂同樣都是合成材料。而從碳水化合物得到的葡萄糖，卻是較為主要的材料，動植物油脂反而居於次要。而且動植物油脂的攝入量又遠低於碳水化合物的攝入量。

也就是說，攝入過量脂肪，並不比攝入過量碳水化合物，以及過量蛋白質更容易導致肥胖。

根據“貝雷”書中介紹，“美國心臟協會”推薦，人體攝入脂肪能量應為不高於總攝入能量的30%。

如以成人日消耗能量為1800～2200千卡/天估計，每天攝入油脂應為60～73.3克。

因此，“中國居民膳食指南”推薦25～30克/天是遠不夠的。

（附英文）

《Fat has little to do with obesity》

(discuss with Mr. Bruce a, etc.)

Huang Xuezhang 

(November 8, 2021)

Mr. brucc a et al. Wrote in Chapter 7, section 4 of 《Bailey, oil chemistry and technology 》prepared by him:

"Although people have many doubts about the causes of obesity, there is still evidence that the chronic imbalance of energy metabolism causing obesity is mostly caused by the calories of fat (4.1 introduction)".

"The poor satiety of fat in the diet will selectively cause obesity. Unlike carbohydrates, protein and alcohol, the human body has poor regulation of fat oxidation and metabolism. The increased fat in the diet will not accelerate its own oxidation, but promote the storage of excess fat into adipose tissue.

Therefore, fat is the main dietary factor causing long-term positive energy balance and obesity. (4.7 conclusion) ".

The above words mean that obesity is caused by excessive intake of fat for the following reasons:

1. Due to the poor satiety of fat, you may mistakenly think you are not full and overeat, resulting in obesity.

2. Excessive fat intake, excess fat can not be oxidized and consumed, and is stored in adipose tissue, leading to obesity.

3. The human body's ability to regulate the oxidative metabolism of fat is worse than that of carbohydrate and protein. Therefore, the energy required for human physiological activities is preferentially obtained from the oxidative metabolism of sugar and protein, while the oxidative metabolism of fat is delayed and ignored, resulting in fat accumulation and obesity.

However, these conclusions are debatable.

1. Poor satiety of fat does not necessarily lead to overeating, which is just a problem of eating habits.

2. Animal and vegetable fats taken from the outside cannot be stored directly. What the human body stores must be their own unique fats synthesized by themselves.

As the German philosopher Leibniz said, "there are no two identical leaves in the world". Everyone's fat structure characteristics will not be exactly the same, let alone directly store animal and plant fat.

3. The oxidative metabolic pathways of fat, sugar (starch) and protein are basically the same. They are first converted to acetyl coenzyme A, and then completely oxidized to carbon dioxide and water through the "tricarboxylic acid cycle" and release energy.

Oil contains carboxyl and double bond active groups. The speed and "controllability" of oxidative metabolism should be higher than that of sugars and proteins, not lower than.

Therefore, when the human body is engaged in physical and mental activities, the energy required first comes from the oxidative metabolism of fat, followed by the oxidation of sugar and protein.

Otherwise, if the priority is to consume sugar and protein ,the last is fat , then the bodybuilders will remove the muscle and leave the fat, so there can be no bodybuilding. Similarly, losing weight through exercise will not be successful.

For more than four years, I drink 40ml vegetable oil on an empty stomach every morning. I really don't feel full. Then I walk continuously and quickly for nearly an hour. I'm still energetic and haven't felt hungry. This shows that fat can not only digest and absorb quickly, but also oxidize and metabolize quickly and release energy.

Therefore, a fat bank with adjustable, flexible revenue and expenditure and high energy efficiency is necessary for the human body.

Obesity is caused by the excess of total nutrients such as carbohydrate, protein, animal and plant fat.

After digestion and absorption, the excess nutrients are synthesized into human fat in the liver or intestinal wall and stored. As long as the total intake is controlled and the human fat storage is not excessive, it will not cause obesity.

In the process of human fat synthesis, carbohydrates, proteins and animal and vegetable oils are also synthetic materials. Glucose obtained from carbohydrates is the dominant material, while animal and vegetable oils are secondary. Moreover, the intake of animal and vegetable oils is far lower than that of carbohydrates.

In other words, eating too much fat is not more likely to lead to obesity than eating too much carbohydrates and too much protein.

According to the introduction in Bailey's book, the American Heart Association recommends that the body's fat energy intake should not be higher than 30% of the total energy intake.

If it is estimated that the daily energy consumption of adults is 1800 ~ 2200 kcal / day, the daily intake of oil should be 60 ~ 73.3 G.

Therefore, it is far from enough to recommend 25 ~ 30g / day in the "dietary guidelines for Chinese residents".