【摘自《別被健康常識騙了》,作者井上健二,平安文化】

 蛋一天最多只能吃一個?

任何東西吃太多都不好,但像蛋(雞蛋)這樣「一天最多一個」,被明確限定數量的食品也很少見。蛋是營養價值很高的食品。一顆蛋裡面包含了大約三週便要孵化出小雞所必需的營養,因此營養非常均衡,有「完全食品」之稱。

蛋尤其是優秀的蛋白質來源,一顆蛋(50g)當中,就含有約6公克的蛋白質。蛋白富含蛋白質,均衡含有人類體內無法自行合成的必需胺基酸。誠如蛋白質的名稱,就是「蛋白」的意思。除此之外,還含有維生素A、B群、D,以及鐵、鋅等礦物質。

另一方面,蛋黃的脂肪多,一個約含5公克的脂肪。而其中又含有約200毫克的膽固醇。而不敢多吃蛋的人,擔心的就是膽固醇。

 

吃了蛋,膽固醇也不會升高

膽固醇是一種只存在於動物性脂肪中的脂質,為身體所必需的營養素。

由於是不可或缺的營養素,因此膽固醇的量會被控制在一定的範圍內。飲食所攝取的膽固醇減少,肝臟製造的膽固醇就增加。相反的,飲食所攝取的膽固醇增加,肝臟製造的膽固醇就減少。

吃蛋會使膽固醇值上升,是近一百年前俄國進行的實驗所產生的誤解。俄國病理學家阿尼奇可瓦持續餵食兔子含有膽固醇的飼料,發現兔子血管內的膽固醇值上升了。

然而,兔子的實驗結果無法直接引用在人身上。膽固醇只存在於動物性脂肪中,而兔子是草食性動物,平日並不會攝取膽固醇。兔子所需的膽固醇全部都由體內合成,所以因應攝取量而調整膽固醇的功能並不發達。因此當兔子食用含有大量膽固醇的飼料之後,膽固醇便會在血管中累積。

 

其實膽固醇並不壞

人體內進行膽固醇的合成與分解的,是肝臟。食物所含的膽固醇最後也會送到肝臟。

血液中的膽固醇分為LDL膽固醇與HDL膽固醇。LDL將必要的膽固醇從肝臟運送到組織,HDL則將多餘的膽固醇從組織運回肝臟。LDL多,則血液中的膽固醇增多,HDL多,則血液中的膽固醇會減少,因此有些人會將LDL稱為壞膽固醇,HDL稱為好膽固醇其實兩者都是人體所必需的,因此本來都是好的。我們想避免的,是LDL與HDL的不平衡。

而近年發現,蛋白中所含的胱氨酸(cystine,胺基酸的一種),可減少血液中過多的LDL。而蛋黃中一種叫做卵磷脂的脂肪(磷脂質),也具有減少多餘膽固醇的功用。

「日本人飲食攝取基準(二○一○年版)」中,膽固醇的一日建議攝取量,男性最多為750毫克,女性為600毫克。蛋一個約含200毫克的膽固醇,所以三個還在建議值內。若是膽固醇值在正常範圍內的健康成人,就算哪天吃了二個以上的蛋也無妨。

有些人相信膽固醇值越低越好,但膽固醇過多過少都有礙健康。膽固醇值過低,會增加腦中風的發生率,而且現在已知每100毫升的血液中,總膽固醇值未達180毫克,死亡率會上升。

 

 

Eggs and Cholesterol – How Many Eggs Can You Safely Eat?

Woman With Basket of EggsEggs are among the most nutritious foods on the planet.

Just imagine… a whole egg contains all the nutrients needed to turn a single cell into an entire baby chicken.

However, eggs have gotten a bad reputation because the yolks are high in cholesterol.

In fact, a single medium sized egg contains 186 mg of cholesterol, which is 62% of the recommended daily intake.

People believed that if you ate cholesterol, that it would raise cholesterol in the blood and contribute to heart disease.

But it turns out that it isn’t that simple. The more you eat of cholesterol, the less your body produces instead.

Let me explain how that works…

How Your Body Regulates Cholesterol Levels

Eggs in a Basket

Cholesterol is often seen as a negative word.

When we hear it, we automatically start thinking of medication, heart attacks and early death.

But the truth is that cholesterol is a very important part of the body. It is a structural molecule that is an essential part of every single cell membrane.

It is also used to make steroid hormones like testosterone, estrogen and cortisol.

Without cholesterol, we wouldn’t even exist.

Given how incredibly important cholesterol is, the body has evolved elaborate ways to ensure that we always have enough of it available.

Because getting cholesterol from the diet isn’t always an option, the liver actually produces cholesterol.

But when we eat a lot of cholesterol rich foods, the liver starts producing less (12).

So the total amount of cholesterol in the body changes only very little (if at all), it is just coming from the diet instead of from the liver (34).

Bottom Line: The liver produces large amounts of cholesterol. When we eat a lot of eggs (high in cholesterol), the liver produces less instead.

What Happens When People Eat Several Whole Eggs Per Day?

Woman Smiling and Holding a Fried Egg

For many decades, people have been advised to limit their consumption of eggs, or at least of egg yolks (the white is mostly protein and is low in cholesterol).

Common recommendations include a maximum of 2-6 yolks per week. However, there really isn’t much scientific support for these limitations (5).

Luckily, we do have a number of excellent studies that can put our minds at ease.

In these studies, people are split into two groups… one group eats several (1-3) whole eggs per day, the other group eats something else (like egg substitutes) instead. Then the researchers follow the people for a number of weeks/months.

These studies show that:

    • In almost all cases, HDL (the “good”) cholesterol goes up (678).

 

    • Total and LDL cholesterol levels usually don’t change, but sometimes they increase slightly (9101112).

 

    • Eating Omega-3 enriched eggs can lower blood triglycerides, another important risk factor (1314).

 

  • Blood levels of carotenoid antioxidants like Lutein and Zeaxanthine increase significantly (151617).

 

 

It appears that the response to whole egg consumption depends on the individual.

In 70% of people, it has no effect on Total or LDL cholesterol. However, in 30% of people (termed “hyper responders”), these numbers do go up slightly (18).

That being said, I don’t think this is a problem. The studies show that eggs change the LDL particles from small, dense LDL to Large LDL (1920).

People who have predominantly large LDL particles have a lower risk of heart disease. So even if eggs cause mild increases in Total and LDL cholesterol levels, this is not a cause for concern (212223).

The science is clear that up to 3 whole eggs per day are perfectly safe for healthy people who are trying to stay healthy.

Bottom Line: Eggs consistently raise HDL (the “good”) cholesterol. For 70% of people, there is no increase in Total or LDL cholesterol. There may be a mild increase in a benign subtype of LDL in some people.

Eggs and Heart Disease

Egg

Many studies have looked at egg consumption and the risk of heart disease.

All of these studies are so-called observational studies. In studies like these, large groups of people are followed for many years.

Then the researchers use statistical methods to figure out whether certain habits (like diet, smoking or exercise) are linked to either a decreased or increased risk of some disease.

These studies, some of which include hundreds of thousands of people, consistently show that people who eat whole eggs are no more likely to develop heart disease. Some of the studies even show a reduced risk of stroke (242526).

However… one thing that is worth noting, is that these studies show that diabetics who eat eggs are at an increased risk of heart disease (27).

Whether the eggs are causing the increased risk in diabetics is not known. These types of studies can only show a correlation and it is possible that the diabetics who eat eggs are, on average, less health conscious than those who don’t.

This may also depend on the rest of the diet. On a low-carb diet (by far the best diet for diabetics), eggs lead to improvements in heart disease risk factors (2829).

Bottom Line: Many observational studies show that people who eat eggs don’t have an increased risk of heart disease, but some of the studies do show an increased risk in diabetics.

Eggs Have Plenty of Other Health Benefits Too

Woman smiling and holding an egg

Let’s not forget that eggs are about more than just cholesterol… they’re also loaded with nutrients and have various other impressive benefits:

    • They’re high in Lutein and Zeaxanthine, antioxidants that reduce your risk of eye diseases like Macular Degeneration and Cataracts (3031).

 

    • They’re very high in Choline, a brain nutrient that over 90% of people are lacking in (32).

 

    • They’re high in quality animal protein, which has many benefits – including increased muscle mass and better bone health (3334).

 

  • Studies show that eggs increase satiety and help you lose fat (3536).

Eggs also taste amazing and are incredibly easy to prepare.

So even IF eggs were to have mild adverse effects on blood cholesterol (which they don’t), the benefits of consuming them would still far outweigh the negatives.

Bottom Line: Eggs are among the most nutritious foods on the planet. They contain important brain nutrients and powerful antioxidants that can protect the eyes.

How Much is Too Much?

Chicken and Egg, Smaller

Unfortunately, we don’t have studies where people are fed more than 3 eggs per day.

It is possible (although unlikely) that eating even more than that could have a detrimental effect on health. Eating more than 3 is uncharted territory, so to speak.

However… I did find an interesting case study (a study with only one individual). It was an 88 year old man who consumed 25 eggs per day.

He had normal cholesterol levels and was in very good health (37).

Of course, a study of one doesn’t prove anything, but it’s interesting nonetheless.

It’s also important to keep in mind that not all eggs are the same. Most eggs at the supermarket are from chickens that are raised in factories and fed grain-based feeds.

The healthiest eggs are Omega-3 enriched eggs, or eggs from hens that are raised on pasture. These eggs are much higher in Omega-3s and important fat-soluble vitamins (3839).

Overall, eating eggs is perfectly safe, even if you’re eating up to 3 whole eggs per day.

I personally eat 3-6 whole eggs per day (about 30-40 per week) and my health has never been better.

Given the incredible range of nutrients and powerful health benefits, quality eggs may just be the healthiest food on the planet.

 

 

 

 

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