新的IOM飲食與運動指南:與Joanne R. Lupton博士的訪談


  2002年9月18日編者按:醫學研究所(IOM)在月初發表的新飲食與運動指南,改變建議的總體營養素的百分比,增加其範圍,並建議攝取更少量的碳水化合物,更多的蛋白質,且提出對添加的糖及轉脂酸的特定指南。
  
  總體營養素攝取飲食手冊專門小組(The Panel on Dietary Reference Intakes for Macronutrients)建議,45%到65%來自碳水化合物的熱量,20%到35%來自脂肪的熱量,及10%到35%來自蛋白質的熱量。另外一個顯著的變化是,推薦的運動量,從每天30分鐘增加到一個小時。
  
  Medscape的Laurie Barclay與專門小組主席且為德州College Station的A&M大學教授,Joanne R. Lupton博士進行訪談。以幫助內科醫師瞭解,應該如何給患者建議,關注飲食與運動的新規定。
  
  Medscape:這些建議與以前的建議有何區別?
  Dr. Lupton:專門小組第一次提供不同的總體營養素攝取百分比範圍,而非絕對為碳水化合物、蛋白質與脂肪。如果進行正確量的運動,且有很好的體質指數(BMI),則有可接受的總體營養素比例,能使你保持體重與BMI。這也是第一次建立碳水化合物的每日認可量的建議(recommended daily allowance,RDA)。大多數人按照超過推薦量的每日130g,或520卡路里的碳水化合物的飲食方式,不過由於低碳水化合物飲食的流行,有些人實際上有攝取不足的風險。
  
  另外,在此之前從未說明的問題是,全纖維素攝取量應該是男性每日38 g,女性每日25 g,或14g/1000卡熱量。同時在植物細胞壁發現植物相對完整的飲食纖維,與添加到食品的功能性或處理後纖維間的區別。欲添加功能性纖維在食品中的公司,將不得不向美國食品藥品管理局(FDA)提出申請,以決定其是否可以作為全纖維需要量的一部分。
  
  Medscape:這種變化背後,是何理由?
  Dr. Lupton:21位專門小組成員回顧所有對總體營養素的臨床及生化研究,完成一篇一千頁的文件,對證據進行概述,並證明我們的指南是正確的。我們只根據科學得出結論,並不考慮民眾的預期或當前施行與公共衛生的指南。我們不得不非常謹慎,因為當一個如IOM般權威的機構作出特別的建議時,食品生產廠家可能依據此建議宣傳其產品。
  
  Medscape:運動在此方案中有何作用?
  Dr. Lupton:我們的運動指南引起全國最大的注意,因為我們將建議數量從每天三十分鐘的體育運動,增加到每天一個小時,我們根據雙次標定水試驗的生化數據,而不是以前使用的飲食與運動記錄作出建議。
  
  生化數據清楚地顯示,經常參加體育活動的人可以保持BMI,並且比久坐的人更能預防心臟病。運動程度越激烈,則所需要做的事情就越少,而且所有的活動都包括在內:園藝,家務,散步或爬樓梯。不過,如果一直參加有氧運動訓練班的運動,其效果比只在屋子堥咧茖咱h更大些。
  
  僅做參考:每天一小時,每小時四英里的散步,即可滿足需求,不過這不必立刻去做。事實上,較好的做法是以短時間的運動,分別在一天之中進行,而時間總和為一小時。
  
  這替代早期必須保持特定的目標心率一段時間,才能有好效果的指南。另一個極端是一周五個工作日總是坐在桌前,而在周末運動的人,在周日或周六進行四小時的運動。即使是他們也應該每天進行一小時的運動。
  
  Medscape:如何根據年齡,性別,運動程度或其他因素,而使這些指南因人而異?
  Dr. Lupton:建議50歲之後減少熱量的攝取,並同時減少纖維的需要。在生長階段,孩子們需要高百分比的蛋白質與氨基酸,以幫助肌肉生長。孕婦與哺乳婦女,則需要較高水準的特定總體營養素。
  
  Medscaoe:對於添加糖與轉脂酸的推薦如何?
  Dr. Lupton:天然的糖,例如牛奶中的乳糖與水果中的果糖,與添加到汽水、烘焙食品及糖果中的糖是不同的。我們一直在注意,攝取過多的添加糖正是月來越糟的嚴重問題。
  
  如果在健康的飲食中攝取添加的糖,則因攝取額外的熱量而變胖,而且如果以添加的糖代替天然的糖,例如用蘇打水代替牛奶,最終則會缺少重要的營養物質。添加的糖只是單純的熱量。
  
  事實上,我們進行許多宣傳,將添加糖佔每日熱量攝取總量比值得上限設為25%,因為目前的方針是15-20%。但是科學研究指出,當來自添加糖的總熱量攝取超過25%而非15-20%時,則會突然出現營養素缺乏,例如鈣與維生素A的缺乏,因此,這就是我們設定的限制點。
  
  根據FDA的要求,我們在七月份發佈對於轉脂酸的建議,因為FDA考慮在食物標簽上,註明轉脂酸百分比的資訊。文獻顯示,轉脂酸的作用與飽和脂肪酸的作用非常相似,甚至只差一些。我們建議,只要還符合健康飲食,那就攝取越多越好。
  
  Medscape:內科醫師該如何做,才能保證患者聽從這些建議?
  Dr. Lupton:指南可以在網路上得到,有根據身高、年齡、性別、運動以及其他因素推薦飲食攝取。他們也可以買一本書,儘管這本書目前正在編輯,可能在一年內還買不到。不過,在網路上的資訊不會變化。
  
  根據這些表格,醫師可以計算一位患者每天可攝取多少熱量,而不會增加體重,他們可以建議蛋白質、碳水化合物以及脂肪的百分比區間。
  
  如果患者正在食用低卡路里飲食的話,則應該告訴他們,每天攝取的熱量,至少有130克。一般對於所有患者,都應建議儘量多運動,至少每天進行一小時的中等強度的體育運動,減少添加的糖與飽和脂肪的攝取,纖維素攝取的建議量,此指飲食纖維素而非功能纖維素。健康飲食會攝取很多水果,蔬菜與全穀。
  
  Medscape:對於無法從飲食中攝取足夠量的營養物質的人而言,含有纖維素或蛋白質添加物的地位為何?
  Dr. Lupton:我們的責任只討論攝取的食物,而非添加物。不過,曾經考慮設置一個可以承受的氨基酸上限。不過我們認識到,如果只從食物中攝取氨基酸,並聽從其他的指南的話,則不會到達上限,因此未對此設定上限。
  
  很有可能,運動的人或其他以氨基酸為添加物的人,可能會超出這個上限,不過目前尚未提到這個問題。類似患有腫瘤或其他限制飲食攝取的慢性疾病患者,理論上可以從補充物中受益,不過我們的責任是制定健康個體的飲食與運動的建議。
  

New IOM Diet And Exercise Guid

By Laurie Barclay, MD
Medscape Medical News

Sept. 18, 2002 — Editor's Note: New guidelines for diet and exercise issued earlier this month by the Institute of Medicine (IOM) change recommended macronutrient percentages and widen the range, suggest less carbohydrate and more protein than previous recommendations, and issue specific guidelines against added sugars and transfatty acids.

The Panel on Dietary Reference Intakes for Macronutrients suggested that 45% to 65% of calories come from carbohydrates, 20% to 35% from fat and 10% to 35% from protein. Another significant change is to increase recommended exercise requirements from 30 minutes to one hour per day.

Medscape's Laurie Barclay interviews panel chair Joanne R. Lupton, PhD, a professor of nutrition at Texas A&M University in College Station, to help physicians understand what to recommend to their patients concerning new prescriptions for diet and exercise.

Medscape: How do these recommendations differ from earlier recommendations?

Lupton: For the first time, the panel provided percentage ranges for intake of different macronutrients rather than absolute numbers of carbohydrates, proteins, and fats. If you do the right amount of exercise and have a good [body mass index (BMI)], there is an acceptable range of macronutrient proportions that will enable you to maintain your weight and BMI.

This is also the first time that we've established a [recommended daily allowance (RDA)] for carbohydrates. Most people eat way in excess of the recommended 130 g/day, or 520 calories from carbohydrates, anyway, but thanks to the popularity of low carbohydrate diets, some people are actually in danger of not getting enough.

Another area that's never been addressed before is the total fiber guideline of 38 g/day for men and 25 g/day for women, or 14 g per 1,000 calories, accompanied by a distinction between dietary fiber found in plants left relatively intact in the plant cell wall, and functional or processed fiber which is added to foods. Companies wanting to add functional fiber will have to petition the [Food and Drug Administration (FDA)] to determine whether it can be considered as part of the total fiber requirement.

Medscape: What was the rationale behind the changes?

Lupton: The 21 panel members reviewed all the literature on clinical and biochemical human studies concerning macronutrients, and we generated a 1,000 page document summarizing the evidence and justifying our guidelines. We came to our conclusions based on the science only, and kept blinders on as to public expectations or existing practices and public health recommendations. We had to be very careful, because when an august body such as the IOM makes a particular recommendation, a food manufacturer could refer to it to make a claim for their product.

Medscape: What role does exercise play in this program?

Lupton: Our exercise guidelines caught the most national attention because we increased the recommended amount from 30 minutes to one hour of physical activity daily. We based this on biochemical data from double-labeled water experiments rather than on diet and exercise diaries used previously.

The biochemical data clearly show that physically active people maintain their BMI and are more protected against heart disease than sedentary people. The more intense your level of activity, the less you have to do, and all activity counts — gardening, housework, walking or climbing stairs. However, if you keep moving in an aerobics class, that counts to a greater extent than just walking around in the house.

As a reference, a total of one hour walking at 4 mph meets the requirement, but it doesn't have to be done all at once. In fact, it's better to break it up throughout the day with short bursts of physical activity that total up to one hour.

This replaces earlier recommendations that you have to maintain a certain target heart rate for a minimum duration to have a beneficial effect. At the other extreme are the weekend warriors who sit behind a desk all day five days a week, then work out or play their sport four hours a day on Saturday and Sunday. Even they should get one hour of physical exercise every day.

Medscape: How do these recommendations differ based on age, gender, activity levels, or other factors?

Lupton: After age 50, recommended calorie intake goes down, so the fiber requirement does also. During the growth spurt, children need higher percentages of proteins and amino acids to help them put on muscle mass. Pregnant and lactating women need higher levels of certain macronutrients.

Medscape: What were the recommendations for added sugars and transfatty acids?

Lupton: There's a big difference between natural sugars, like lactose in milk and fructose in fruit, and added sugars found in soft drinks, baked goods and candy. We're concerned about overconsumption of added sugars — it's a terrible problem which seems to be getting worse instead of better.

If you take in added sugars in an otherwise healthy diet, you'll gain weight because of the extra calories, and if you substitute added sugars for natural sugars, like a soda instead of a glass of milk, you'll end up missing out on important nutrients. Added sugars are just empty calories.

Actually, we got a lot of flack for setting the bar for added sugars at no more than 25% of daily calorie intake, because present recommendations are 15-20%. But the science pointed to deficiencies of nutrients like calcium and vitamin A cropping up when more than 25% of total calories came from added sugars, not at 15-20%, so that's where we placed our limit.

At the FDA's request, we released our recommendations on transfatty acids in July, because the FDA is considering putting information about transfatty acid percentages on food labels. The literature makes it clear that transfatty acids act very similarly or even a little worse than do saturated fats. Our recommendation is to keep intake as low as possible, provided it is still consistent with a healthy diet.

Medscape: What can physicians do to ensure that their patients follow these recommendations?

Lupton: The guidelines are available online and have detailed tables for recommended dietary intakes based on height, age, sex, physical activity and other factors. They can also be purchased as a book, although it's being edited now and may not be available for up to a year. However, the information online won't change.

From these tables, doctors can calculate the number of calories a patient can consume daily without gaining weight, and they can recommend percentage ranges for protein, carbohydrates, and fats.

If patients are on a low carbohydrate diet, they should be counseled to consume at least 130 g of carbs daily. General recommendations for all patients are to keep as active as possible -- at least one hour of moderate physical activity a day — to cut down on added sugars and saturated fats, and to get their recommended fiber intake as dietary fiber rather than functional fiber. If they do that, they'll be eating healthy by default, because they'll be eating lots of fruits, vegetables, and whole grains.

Medscape: What is the role for supplements containing fiber or protein for individuals who cannot consume sufficient quantities in their diet?

Lupton: Our charge was to address food intake only, and not supplements. However, we considered setting a tolerable upper limit (UL) for amino acids. But we realized that you wouldn't reach an UL if you were getting amino acids only from foods and following the other guidelines, so we didn't.

It is possible that body builders or others using amino acid supplements might exceed the UL, but we didn't

    
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