The most basic function of bodily fat is self-storage of food reserves. In prehistoric times, natural selection favored genotypes that could endure harsh conditions by stocking the most fat. With chronic malnutrition being the norm for most of human history, genetics evolved to favor fat storage. So when did body fat become problematic? The negative impacts of being overweight were not even noted in medical literature until as late as the 18th century. Then, technological advances coupled with public health measures resulted in the betterment of the quantity, quality, and variety of food. Sustained abundance of good food enabled a healthier population to boom economically. Output increased, and with it, leisure time and waistlines. By the mid 19th century, being excessively overweight, or obese, was recognized as a cause of ill health, and another century later, declared deadly. What is the distinction between being overweight and being obese? A calculation called the BMI breaks it down for us. For example, if someone weighs 65 kilgorams and is 1.5 meters tall, they have a BMI of about 29. Obesity is a condition of excess body fat that occurs when a person's BMI is above 30, just over the overweight range of 25 to 29.9. While BMI can be a helpful estimate of healthy weight, actual body fat percentage can only really be determined by also considering information like waist circumference and muscle mass. Athletes, for instance, have a naturally higher BMI. So how does a person become obese? At its most basic, obesity is caused by energy imbalance. If the energy input from calories is greater than the energy output from physical activity, the body stores the extra calories as fat. In most cases, this imbalance comes from a combination of circumstances and choices. Adults should be getting at least 2.5 hours of exercise each week, and children a whole hour per day. But globally, one in four adults and eight out of ten adolescents aren't active enough. Calorie-dense processed foods and growing portion sizes coupled with pervasive marketing lead to passive overeating. And scarce resources, and a lack of access to healthy, affordable foods creates an even greater risk in disadvantaged communities. Yet, our genetic makeup also plays a part. Studies on families and on separated twins have shown a clear causal hereditary relationship to weight gain. Recent studies have also found a link between obesity and variations in the bacteria species that live in our digestive systems. No matter the cause, obesity is an escalating global epidemic. It substantially raises the probability of diseases, like diabetes, heart disease, stroke, high blood pressure, and cancer. It affects virtually all ages, genders, and socioeconomic groups in both developed and developing countries. With a 60% rise in child obesity globally over just two decades, the problem is too significant to ignore. Once a person is obese, the climb to recovery becomes progressively steeper. Hormonal and metabolic changes reduce the body's response to overeating. After losing weight, a formerly overweight person burns less calories doing the same exercises as a person who is naturally the same weight, making it much more difficult to shed the excess fat. And as people gain weight, damage to signaling pathways makes it increasingly difficult for the brain to measure food intake and fat storage. There is, however, some evidence that well-monitored, long-term changes in behavior can lead to improvements in obesity-related health issues. And weight loss from sustained lifestyle changes, or invasive treatments like bariatric surgery, can improve insulin resistance and decrease inflammation. What was once an advantage for survival is now working against us. As the world's population continues to slow down and get bigger, moving and consciously eating our way towards a healthier weight is essential to our overall well-being. And with the epidemic affecting every country in the world for different socioeconomic reasons, obesity cannot be seen as an isolated issue. More global measures for prevention are essential to manage the weight of the world.
體脂肪的最基本功能 乃是自我保存備份食物 在史前時代,物競天擇偏愛 能夠承受嚴峻環境 儲存最多脂肪的基因型態 人類歷史大多時候 長期的營養不良是常態 所以基因的發展偏愛儲存脂肪 體脂肪變成問題,始自何時呢? 醫學文獻先前並未注意到 超重的負面影響 直至 18 世紀 技術進步和公共衛生措施 大幅改善食物的數量、質量、和種類 源源不絕的良好食物 使得健康人口的數目大增 產量增加使得空閒時間 和腰圍也增加了 到了 19 世紀中葉 過重或肥胖 被認為是健康狀況不佳的原因 再過一個世紀 肥胖被昭示為致命 怎麼區分過重和肥胖? 可用身體質量指數 BMI 計算來分類 例如,某人重 65 公斤 身高 150 公分 那他的 BMI 大約 29 體脂肪過多的狀態 BMI 大於 30 的人是肥胖 若介於 25 到 29.9 間就是超重 雖然 BMI 能輔助估算健康的體重 但實際的體脂率必須計入 其他的資訊,例如腰圍 和肌肉質量 例如,運動員自然有較高的 BMI 人是怎麼變肥胖的? 基本上,肥胖是能量失衡造成的 如果吃進的卡路里 超出體力活動用掉的 身體就會把多餘的卡路里 以脂肪的形式儲存起來 多數情況下,失衡來自於環境 和選擇 成年人每星期 至少應運動 2.5 小時 孩子每天整整一個小時 但全球四分之一的成年人 和十分之八的青少年 體力活動不足 高熱量的加工食品 和不斷增大的份量 加上無處不在的行銷 致使被動地暴飲暴食 資源稀少 和缺乏獲得健康 經濟實惠食品的管道 使得弱勢群體面臨更大的風險 我們的基因組成也起了一些作用 研究成長在不同家庭的雙胞胎 明確顯示遺傳和體重增加的關係 最近的研究還發現 肥胖與生活在消化系統內的 細菌物種變異有關聯 不計起因,肥胖是 不斷升級的全球性流行病 它大大提高罹患疾病的機率 像糖尿病 心臟病 中風 高血壓 和癌症 它影響了幾乎所有的年齡 性別和社會經濟群體 發達國家和發展中國家都一樣 在短短二十年間 全球的肥胖兒童增加了 60% 問題已大到不能被忽視的地步 人一旦肥胖 要恢復原來的體重變得非常困難 荷爾蒙和新陳代謝的變化 降低身體對過量進食的反應 曾經超重的人 減肥後做同樣的運動 比原本正常有著同樣體重的人 消耗掉更少的熱量 更難以擺脫多餘的脂肪 隨著人們發胖 受損的神經訊號通路 使得大腦更難以衡量 食物的攝入和脂肪的儲存 然而,有證據顯示 充分監督和長期的行為改變 可改善與肥胖相關的健康問題 經由持續生活方式改變的減肥 或像減肥手術之類的侵入性治療 可以改善胰島素抗性並減少炎症 曾是生存優勢,現在卻對我們不利 隨著世界人口的腳步持續放緩 塊頭越來越大 活動和合理的進食 是通往健康體重的方式 對我們的整體福祉至關重要 儘管這種流行病因不同的社經原因 影響著世界上每一個國家 肥胖不能被看作孤立的問題 全球性的預防措施 是管理世界體重的要領