We hear about calories all the time. How many calories are in this cookie? How many are burned by 100 jumping jacks, or long distance running, or fidgeting? But what is a calorie, really, and how many of them do we actually need? Calories are a way of keeping track of the body's energy budget. A healthy balance occurs when we put in about as much energy as we lose. If we consistently put more energy into our bodies than we burn, the excess will gradually be stored as fat in our cells, and we'll gain weight. If we burn off more energy than we replenish, we'll lose weight. So we have to be able to measure the energy we consume and use, and we do so with a unit called the calorie. One calorie, the kind we measure in food, also called a large calorie, is defined as the amount of energy it would take to raise the temperature of one kilogram of water by one degree Celsius. Everything we consume has a calorie count, a measure of how much energy the item stores in its chemical bonds. The average pizza slice has 272 calories, there are about 78 in a piece of bread, and an apple has about 52. That energy is released during digestion, and stored in other molecules that can be broken down to provide energy when the body needs it. It's used in three ways: about 10% enables digestion, about 20% fuels physical activity, and the biggest chunk, around 70%, supports the basic functions of our organs and tissues. That third usage corresponds to your basal metabolic rate, a number of calories you would need to survive if you weren't eating or moving around. Add in some physical activity and digestion, and you arrive at the official guidelines for how many calories the average person requires each day: 2000 for women and 2500 for men. Those estimates are based on factors like average weight, physical activity and muscle mass. So does that mean everyone should shoot for around 2000 calories? Not necessarily. If you're doing an energy guzzling activity, like cycling the Tour de France, your body could use up to 9000 calories per day. Pregnancy requires slightly more calories than usual, and elderly people typically have a slower metabolic rate, energy is burned more gradually, so less is needed. Here's something else you should know before you start counting calories. The calorie counts on nutrition labels measure how much energy the food contains, not how much energy you can actually get out of it. Fibrous foods like celery and whole wheat take more energy to digest, so you'd actually wind up with less energy from a 100 calorie serving of celery than a 100 calorie serving of potato chips. Not to mention the fact that some foods offer nutrients like protein and vitamins, while others provide far less nutritional value. Eating too many of those foods could leave you overweight and malnourished. And even with the exact same food, different people might not get the same number of calories. Variations in things like enzyme levels, gut bacteria, and even intestine length, means that every individual's ability to extract energy from food is a little different. So a calorie is a useful energy measure, but to work out exactly how many of them each of us requires we need to factor in things like exercise, food type, and our body's ability to process energy. Good luck finding all of that on a nutrition label.
我們不時聽到「卡路里」 這個餅乾裡有多少卡路里呢? 做 100 個開合跳、長跑或是仰臥起坐 會燃燒掉多少卡路里呢? 可是 1 卡路里究竟代表什麼呢? 還有我們實際上需要多少卡路里呢? 卡路里是一種監測人體能量 消耗量的方法 當我們攝入的能量和消耗的能量相同, 就是一種較為健康的平衡。 可是,如果我們不斷地攝入比我們 所燃燒的能量還要多的時候 多出來的能量將會逐漸地被當作 脂肪儲存在我們的細胞裡 導致體重增加 相反,如果我們消耗的能量超過 攝入的能量,體重就會減輕 所以我們需要一種方法量化 我們所攝入和消耗的能量 於是,我們引入「卡路里」這個概念 用於量化食物所含熱量, 1 千卡路里又叫做 1 大卡 其定義為:1 公升的水 溫度升高一攝氏度所需要的能量 我們吃進去的所有食物有卡路里值, 它指的是破壞食物分子中的 化學鍵所需的能量 一片普通大小的披薩切片有 272 大卡 一片土司大概有 78 大卡 一顆蘋果有 52 大卡 這些能量在消化時被釋放出來, 並儲存在分子中。 當人體需要能量時, 分子就會釋放其中的能量。 能量可用在三個方面: 其中10%用於消化; 20%用於日常活動 剩餘最多的70%用於維持 體內器官和組織的基本運作 第三種用途與你的基礎代謝率有關 假使你不吃不動 還是需要這些能量維持生命體征 根據官方指南, 加上日常活動和消化過程, 一般人每人每天所需的平均能量為: 女性 2,000 大卡;男性 2,500 大卡 這些數據是基於人的平均重量、 活動量、肌肉量等要素計算得出。 但這是不是就意味著,每個人 都應該攝入 2,000 大卡左右的卡路里數呢? 不必然啦! 要是我們進行高耗能活動 像是「環法自行車賽」 那麼一天所需要的能量就有 9,000 大卡 懷孕需要比平常稍多一些的卡路里 而年長者通常有比較緩慢的基礎代謝率 能量的燃燒會更平緩 因此所需要的是比較少的卡路里 開始計算卡路里前 你需要知道一些東西 營養標示中的卡路里值表示 食物含有了多少能量 而不是你實際上可以 從中得到多少能量 芹菜和全麥等富含膳食纖維的食物 要用上更多的能量來消化 所以實際上比起享用 100 大卡的洋芋片 享用 100 大卡的芹菜 你會獲得較少的能量做結 更別提事實有些食物供應了像是 蛋白質與維他命等營養 際此同時其他的食物提供 遠遠較低的營養價值 吃太多那些低營養的食物 只會讓你超重和營養不良 即便食用完全相同的食物 不同之人也不會攝入 相同的能量 人體內酶水平,腸道細菌甚至是腸道長度差異 都會影響人體從食物中獲得的能量多少。 在計算能量時,卡路里值確實很重要, 但是要計算出我們每個人 到底需要多少卡路里 就應該同時考慮運動量、食物種類 以及身體處理能量的能力等因素。 祝你幸運地在營養標示上 找到所有這一切的東西!