Which of these has the least carbohydrates? This roll of bread? This bowl of rice? Or this can of soda? It's a trick question. Although they may differ in fats, vitamins, and other nutritional content, when it comes to carbs, they're pretty much the same. So what exactly does that mean for your diet? First of all, carbohydrate is the nutritional category for sugars and molecules that your body breaks down to make sugars. Carbohydrates can be simple or complex depending on their structure. This is a simple sugar, or monosaccharide. Glucose, fructose, and galactose are all simple sugars. Link two of them together, and you've got a disaccharide, lactose, maltose, or sucrose. Complex carbohydrates, on the other hand, have three or more simple sugars strung together. Complex carbohydrates with three to ten linked sugars are oligosaccharides. Those with more than ten are polysaccharides. During digestion, your body breaks down those complex carbohydrates into their monosaccharide building blocks, which your cells can use for energy. So when you eat any carbohydrate-rich food, the sugar level in your blood, normally about a teaspoon, goes up. But your digestive tract doesn't respond to all carbohydrates the same. Consider starch and fiber, both polysaccharides, both derived from plants, both composed of hundreds to thousands of monosaccharides joined together, but they're joined together differently, and that changes the effect they have on your body. In starches, which plants mostly store for energy in roots and seeds, glucose molecules are joined together by alpha linkages, most of which can be easily cleaved by enzymes in your digestive tract. But in fiber, the bonds between monosaccharide molecules are beta bonds, which your body can't break down. Fiber can also trap some starches, preventing them from being cleaved, resulting in something called resistant starch. So foods high in starch, like crackers and white bread, are digested easily, quickly releasing a whole bunch of glucose into your blood, exactly what would happen if you drank something high in glucose, like soda. These foods have a high glycemic index, the amount that a particular food raises the sugar level in your blood. Soda and white bread have a similar glycemic index because they have a similar effect on your blood sugar. But when you eat foods high in fiber, like vegetables, fruits, and whole grains, those indigestible beta bonds slow the release of glucose into the blood. Those foods have a lower glycemic index, and foods like eggs, cheese, and meats have the lowest glycemic index. When sugar moves from the digestive tract to the blood stream, your body kicks into action to transfer it into your tissues where it can be processed and used for energy. Insulin, a hormone synthesized in the pancreas, is one of the body's main tools for sugar management. When you eat and your blood sugar rises, insulin is secreted into the blood. It prompts your muscle and fat cells to let glucose in and jump starts the conversion of sugar to energy. The degree to which a unit of insulin lowers the blood sugar helps us understand something called insulin sensitivity. The more a given unit of insulin lowers blood sugar, the more sensitive you are to insulin. If insulin sensitivity goes down, that's known as insulin resistance. The pancreas still sends out insulin, but cells, especially muscle cells, are less and less responsive to it, so blood sugar fails to decrease, and blood insulin continues to rise. Chronically consuming a lot of carbohydrates may lead to insulin resistance, and many scientists believe that insulin resistance leads to a serious condition called metabolic syndrome. That involves a constellation of symptoms, including high blood sugar, increased waist circumference, and high blood pressure. It increases the risk of developing conditions, like cardiovascular disease and type II diabetes. And its prevalence is rapidly increasing all over the world. As much as 32% of the population in the U.S. has metabolic syndrome. So let's get back to your diet. Whether your food tastes sweet or not, sugar is sugar, and too many carbs can be a problem. So maybe you'll want to take a pass on that pasta sushi roll pita burrito donut burger sandwich.
這些那一個所含的 醣類(碳水化合物)最少? 這條麵包? 這碗飯? 還是這罐蘇打汽水? 這是個故弄玄虛的問題 雖然它們在脂肪、維生素 及其他營養成份可能不同 但當說到醣類(碳水化合物) 它們就相去無幾了 所以對你的飲食真正的意義是什麼? 首先,糖在營養分類中屬於醣類 身體分解醣類以生成糖 根據它們的結構,醣類 可以是簡單的或是複雜的 這是一種單醣 (simple sugar) 或單醣 (monosaccharide) 葡萄糖、果糖和半乳糖全都是單醣 將它們任兩個連結,你就會 得到一種雙醣 (disaccharide) ─ ─ 乳糖、麥芽糖或蔗糖 另一方面,複雜醣類 具有三種或更多的單醣串在一起 由三個至十個單醣連結的複雜醣類 稱為寡醣 (oligosaccharides) 而超過十個以上的稱為 多醣 (polysaccharides) 當消化食物時 身體會將複雜醣類分解 成為單醣分子 供細胞做為能量使用 所以當你吃任何富含醣類的食物時 你的血糖濃度, 一般大約一茶匙,就會上升 但你的消化道並不是對 所有醣類的反應都一致 就澱粉和纖維而言 兩者都是多醣 都是來自植物 都是由幾百個到幾千個 單醣連結在一起組成的 但它們結合的方式不同 就會改變作用在你身體的結果 澱粉 ─ 是植物在根及種子中 大部份的能量儲存方式 其葡萄糖分子以 阿爾法鍵 (alpha linkage) 連結在一起 大多數很容易被消化道中的酵素分割 但是纖維,單醣分子間的鍵 是貝他鍵 (beta bonds) 身體無法分解 纖維也能將一些澱粉夾於其中 避免它們被分割 而形成所謂的阻抗澱粉 (resistant starch) 所以澱粉含量高的食物 如薄脆餅乾與白麵包 很容易被消化 會迅速地釋放一大堆葡萄糖進入血中 如果喝了含大量葡萄糖飲料, 像蘇打汽水也會發生完全一樣的情形 這些食物具有高升糖指數 升糖指數是指 某一特定食物升高血糖的數值 蘇打汽水和白麵包具有相似的升糖指數 因為它們對於血糖有相似的影響 但當吃高纖食物時 ─ 像蔬菜、水果和全穀類 那些難以消化的貝他鍵 減緩了葡萄糖釋入血中 這些食物具有較低的升糖指數 像雞蛋、乳酪和肉類的升糖指數最低 當糖自消化道進入血液 身體會開始將它轉送到組織 在那裡它會被處理,並作為能量使用 胰島素,一種在胰臟合成的荷爾蒙 是身體處理糖分的主要工具之一 當進食而血糖上升時 胰島素會被分泌而進入血中 它會促使肌肉和脂肪細胞 讓葡萄糖進入 快速開始將糖轉換為能量 每一單位胰島素降低血糖的程度 可幫我們了解所謂的「胰島素敏感性」 一定單位量的胰島素 降低血糖的程度愈大 即你對胰島素的敏感性就愈大 如果胰島素的敏感性下降 就是眾所周知的「胰島素阻抗」 胰臟仍會釋出胰島素 但細胞 ─尤其是肌肉細胞─ 對它的反應越來越少 所以血糖無法下降 而血中胰島素卻持續上升 長期食用大量醣類 可能導致胰島素阻抗 許多科學家相信胰島素阻抗 會導致一種嚴重狀況 稱為「代謝症候群」 會出現一系列的症狀 包括高血糖 腰圍增加 及高血壓 它會增加疾病形成的風險 如心臟血管疾病 及第二型糖尿病 而它的罹病率在全世界快速地增加中 在美國多達 32 % 的人口患有代謝症候群 所以讓我們回到你的飲食 無論你的食物嚐起來甜不甜 糖就是糖 太多的醣類會是個問題 所以你也許願意對 義大利麵、壽司卷、皮塔餅、玉米煎餅、 甜甜圈做成的漢堡三明治,視而不見吧!