But just how accurate are they anyway?

但它們到底多準確呢？

Hey, guys, Julia here for DNews.

大家好，我是 DNews 的 Julia。

Food labels are great.

食品標示很棒。

They give you an estimate of how many calories are in any certain food.

它讓你吃東西時可以知道自己攝取了多少卡路里。

But they have a teeny bit of a flaw.

但它們有一個小小的缺陷。

They fail to take into account cooking.

它們沒有考量到食物的烹調方式。

So we end up with a system that likely overestimates the calories available in unprocessed foods and underestimates the calories in processed food.

所以這讓我們總是高估未加工食物的卡路里量，且低估加工食品的卡路里量。

The way we currently count calories is based on the Atwater System, which is at least a hundred years old.

我們目前是基於「艾特瓦特系統」去計算卡路里，而它至少有 100 年的歷史了。

The System standardized the idea of the amount of energy available in food, 9 calories in a gram of fat or 4 calories in every gram of protein.

這個系統訂定各種食物中成份固定量所含的能量，脂肪每克 9 大卡，蛋白質每克 4 大卡。

But this measures the availability of energy in food, not the digestibility.

但理論上這只計算到食物上能量的可利用性，沒有考量到它的可消化程度。

A calorie is a unit of energy.

卡路里是能量的單位。

It's technically the amount of energy needed to heat up a kilogram of water by 1 degree Celsius.

理論上來說，1 大卡是使 1 公斤的水提高 1℃ 所需要的能量。

Our body burns calories in food through metabolizing the carbohydrates and proteins and whatnot into smaller molecules our body can use as energy.

我們身體通過代謝來燃燒碳水化合物和蛋白質等物質所含的卡路里，並把它們轉變成更小的分子讓我們的身體可以作為能量使用。

Cooking food changes how many calories are digestible.

而食物的烹調方式會影響它的可消化性。

Take potatoes for example.

拿馬鈴薯舉例。

When raw, the sugar molecules in potatoes are too tightly packed for our digestive system to handle.

當生吃時，馬鈴薯的醣分子因為太緊密連結的關係，使得我們很難去消化。

Cooking causes the starches in the potato to gelatinize.

而經烹調後會使馬鈴薯中的澱粉變為膠狀。

That process allows us to access the sugars stored in the starch, so we get more calories out of the cooked potato.

這道程序會讓我們更能去吸收澱粉裡的醣分子，所以當我們在吃煮過的馬鈴薯時攝取的卡路里也較高。

On top of that, the type of cooking method might change the chemistry of food as well, whether it's boiled, baked, or microwaved.

除此之外，烹調的方法還可能去改變食物中的分子結構，無論是用煮的、用烤的或是用微波的。

On the other hand, digesting raw food takes work: A stick of celery might have 10 calories, but the chewing and digesting burns about half of them.

另外，消化生食時會需要額外的能量，像是一根芹菜裡可能有 10 卡路里，但在嚼它和消化它的過程中可能就先消耗掉 5 卡路里了。

All that work means there are fewer calories for your body to absorb for energy.

這代表在吃這些生食時，我們會吸收到較少的卡路里。

But before you go nibbling on an all-carrot diet, consider this:

但如果你因為這樣就只想去吃一堆生紅蘿蔔，你應該考慮一下：

For our ancestors, cooking meant the difference between life and death.

對我們的祖先來說，烹調食物意味著生與死的差別。

The invention of a cooked meal might have changed everything.

「烹調」這個發明可以說是改變了一切。

Cooking food provided more energy and led to humans with bigger brains and bigger babies.

食物經過烹調可以提供更多的能量，使人類演化出更健全的大腦，更健康的嬰兒。

And people who consume an all-raw diet now might not be getting enough calories, even when eating food packed with nutrients.

而如果有人現在只吃生食，就算那些食物都非常有營養，也還是有可能攝取不到足夠的熱量。

Some women on an all-raw diet get irregular menstrual cycles—a sign of undernourishment—not to mention the bacteria of your gut steal a few of the calories for themselves.

有些婦女也在吃全生食的過程中出現亂經、營養不良等症狀，更不用說你吃進去的細菌在你腸道裡自己偷偷消化了多少卡路里。

So the exact number of calories you're getting is affected by way too many factors for those labels to be truly accurate.

所以有太多可能的因素會去導致你實際吸收的熱量，與標示上的熱量不太一樣。

But while modifications to the Atwater system have improved it some over the years, there's still no real alternative.

雖然經過改良艾特沃系統後這情況有稍微得到改善，但我們還是沒有什麼其他計算熱量的選擇。

So until nutrition scientists come up with a better calorie counting system, take food labels with a grain of salt.

因此，除非營養科學家們想出了一個更好的卡路里計算系統，食物標示參考參考就好啦。

See what I did there? Grain of salt? It's a... pun... ok.

看我做了什麼？一撮鹽 / 持保留態度？這是...雙關語...

Switching gears for a second, I wanted to let you know that tomorrow, Trace, Amy, and Ian are gonna be chatting with a real-live astronaut about what it's like to live and work in space.

題外話一下， 我想跟你們說，就在明天 Trace、Amy 跟 Ian 就要訪談一位太空人，聊聊真正在太空中工作和生活是什麼感覺。

And if you wanna hang out with us space nerds, be sure to RSVP using the link we've got in the description.

如果你也想一起加入的話，請利用以下連結回覆給我們。

That's at 3 p.m. Eastern time, noon Pacific.

時間訂在東部時間下午三點，中午太平洋時間。

So, do you trust nutritional labels?

所以你現在還相信食物標示嗎？

Do they need to be updated?

你覺得它們應該要更新一下嗎？

Leave your thoughts and comments below, and don't forget to subscribe for more DNews everyday.

請在下面留下您的想法和評論，還有別忘記訂閱我們的頻道鎖定更多每日快訊。