不論蛋白質、脂肪或碳水化合物比率 過多熱量是肥胖的主因


  【24drs.com】1月3日JAMA期刊的新研究認為,不論蛋白質、脂肪和碳水化合物的特定比率,攝食過量是肥胖的重要原因,也是抑制的關鍵;此外,低蛋白質飲食(約5%)特別有危險,導致有保護力的淨體重降低。
  
  Pennington生物醫學研究中心的George Bray醫師等人寫道,這篇研究的主要結果是,熱量比蛋白質更重要,吃過多熱量和體脂肪增加有關。再者,作者寫道,與蛋白質佔飲食熱量15%和25%相比,蛋白質僅提供5%的飲食熱量,其代謝差異為較高的能量消耗比較不會增加體重。
  
  故意給25名健康年輕男性和女性每天增加1000卡熱量、超過56天;過量飲食是根據開始時的體重穩定評估而定。研究設計為單盲、隨機控制試驗,病患在2005年6月至2007年10月住進代謝病房。
  
  先給予病患13-25天的穩定體重飲食,之後隨機分組為:低蛋白質組(佔總量5%)、正常蛋白質組(總量15%)與高蛋白質組(總量25%)。與體重穩定治療相比,增加的蛋白質多提供了40%的熱量,相當於每天954大卡(95%信心區間[CI],每天884 – 1022大卡)。主要結果是使用雙能量X光吸收儀評估身體組成;休息時的能量消耗;總能量消耗。
  
  根據該研究,單純攝取過多熱量導致體脂肪較高。就降低淨體重而言,與正常和高蛋白質飲食相比,低蛋白質飲食證明有害,特別的是,該研究發現,相較於正常蛋白質組(6.05公斤;95% CI,4.84 - 7.26公斤)或高蛋白質組(6.51公斤;95% CI,5.23 - 7.79公斤;P = .002),低蛋白質治療組的體重增加程度顯著較少(3.16公斤;95% CI,1.88 - 4.44公斤)。
  
  當評估這三組的體脂肪時,研究者發現,增加的情況相同,與蛋白質無關。低蛋白質組並未增加休息時的能量消耗、總能量消耗、或淨體重,但是,正常蛋白質或高蛋白質組則有(休息時能量消耗:正常蛋白質飲食-每天160大卡[95% CI,102 – 218大卡/天]、高蛋白質組-每天227大卡[95% CI,165 - 289大卡/天];淨體重:正常蛋白質飲食- 2.87公斤[95% CI,2.11 - 3.62公斤]、高蛋白質組- 3.18公斤[95% CI,2.37 - 3.98公斤])。
  
  編輯評論中,加州大學洛杉磯分校的David Heber博士和Zhaoping Li博士表示,這篇研究強調蛋白質對減重介入的重要性。Heber博士和Li博士寫道,研究強度之一是,它評估了脂肪累積,不只是整體體重增加和身體質量指數,因為他們認為這些可能會產生誤導。
  
  他們寫道,醫師應考慮評估病患的整體脂肪量,而不只是測量體重或身體質量指數,且要注意累積過多脂肪可能引起的併發症。肥胖治療的目標應包括減少脂肪,而不只是減重,且要更加瞭解營養科學。
  
  哥倫比亞大學醫學教授、紐約市聖路加羅斯福醫院肥胖研究中心主任、未參與該研究的Xavier Pi-Sunyer醫師表示,他並不認為脂肪組成可以取代身體質量指數和體重,應該是「吃太多引起體重增加」。
  
  他指出,該研究對肥胖引起的公衛影響有限,我們正致力於減少熱量,而不是過量,此外,多數美國人有12%-15%的熱量來自蛋白質,所以他不擔心足量蛋白質的壓力。
  
  不過,人類行為與代謝研究中心負責人、名譽教授、紐約Rockefeller大學名譽外科主任Jules Hirsch醫師表示,我們試過多種熱量組合,都沒有顯示出因果關係,只有過多熱量顯示與引起肥胖有關,這也可用來設計有效的介入方式。
  
  Hirsch醫師表示,飲食內容的變化並不是最重要的,我們需要的是降低熱量攝取,該研究顯示,低蛋白質飲食對於治療或造成肥胖無關。
  
  資料來源:http://www.24drs.com/professional/list/content.asp?x_idno=6705&x_classno=0&x_chkdelpoint=Y
  

Excess Calories, Not Mix of Protein, Fat, or Carbohydrate, Key in Causing Obesity

By Laura Newman
Medscape Medical News

January 4, 2012 — Excess food consumption, rather than any specific caloric mixture of protein, fat, and carbohydrates, is an important driver of obesity, and will be key in curbing it, suggests new research published in the January 3 issue of JAMA.In addition, diets with low protein (about 5% of consumption) are potentially dangerous, the study revealed, resulting in loss of lean body mass, which is protective.

"The key finding of this study is that calories are more important than protein while consuming excess amounts of energy with respect to increases in body fat," write George Bray, MD, from Pennington Biomedical Research Center, Baton Rouge, Louisiana, and colleagues. Further, the authors write: "a diet providing only 5% of energy from protein was metabolically different with a higher energy cost of weight gain compared with diets that contained 15% and 25% of energy from protein."

Eating in a Controlled Setting

Twenty-five healthy young men and women were intentionally overfed by approximately 1000 extra calories each day for more than 56 days. Overfeeding was determined by using a baseline weight stabilization evaluation. Using a single-blind, randomized controlled trial study design, patients were admitted to the inpatient metabolic unit between June 2005 and October 2007.

Patients first were put on a weight-stabilizing diet for 13 to 25 days, and then randomly assigned to 1 of 3 groups: low protein (about 5% of total diet), normal protein (15% of total diet), and high protein (25% of total diet). In comparison with the weight-stabilization treatment, the added protein provided 40% more energy intake, equivalent to 954 kcal/day (95% confidence interval [CI], 884 - 1022 kcal/day). Primary outcomes were body composition, evaluated using dual energy X-ray absorptiometry; resting energy expenditure; and total energy expenditure.

Effect of Overeating on Outcomes

Excess caloric intake alone resulted in a higher-fat body composition, according to the study. The low-protein diet proved hazardous, compared with the normal- and high-protein diets, in terms of decreased lean body mass. Specifically, the study revealed significantly less weight gain in the low-protein treatment group (3.16 kg; 95% CI, 1.88 - 4.44 kg) compared with the normal-protein (6.05 kg; 95% CI, 4.84 - 7.26 kg) or high-protein (6.51 kg; 95% CI, 5.23 - 7.79 kg; P = .002) treatment groups.

When body fat was evaluated in the 3 treatment groups, researchers found that it increased about the same, regardless of which protein group people were in. People in the low-protein group did not increase their resting energy expenditure, total energy expenditure, or lean body mass, but patients in the normal-protein and high-protein groups did (resting energy expenditure: normal-protein diet, 160 kcal/day [95% CI, 102 - 218 kcal/day] vs high-protein diet, 227 kcal/day [95% CI, 165 - 289 kcal/day]; lean body mass: normal protein diet, 2.87 kg [95% CI, 2.11 - 3.62 kg] vs high-protein diet, 3.18 kg [95% CI, 2.37 - 3.98 kg]).

In an accompanying editorial, David Heber, MD, PhD, and Zhaoping Li, MD, PhD, from the University of California, Los Angeles, stress the importance of protein in weight reduction interventions, which was underscored by the study. One strength of the study, write Drs. Heber and Li, is that it evaluated fat accumulation, not just overall weight increase and body mass index, which they contend can be misleading.

"Clinicians should consider assessing a patient's overall fatness rather than simply measuring body weight or body mass index and concentrate on the potential complications of excess fat accumulation," they write. "The goals for obesity treatment should involve fat reduction rather than simply weight loss, along with a better understanding of nutrition science."

Xavier Pi-Sunyer, MD, professor of medicine at Columbia University College of Physicians and Surgeons in New York City and director of the New York Obesity Research Center, St. Luke's Roosevelt Hospital Center, New York City, told Medscape Medical News that he was not convinced of the merits of fat composition as an alternative body mass index and weight. He was not involved in the study, but said that the "public health message was that eating too much causes weight gain."

He added, "The study would have limited public health impact because with obesity, we are trying to create a caloric deficit, not an excess." In addition, he said, "Most Americans are getting 12% to 15% of their food intake from protein," so he was not concerned about the stress on sufficient protein.

However, Jules Hirsch, MD, professor emeritus and head of the Laboratory of Human Behavior and Metabolism and physician-in-chief emeritus, Rockefeller University, New York, New York, applauded the study for driving home that "no caloric mixture, everything we've tried, nothing has been demonstrated to be causative other than excess total consumption," both in causing obesity and in designing effective interventions.

"What the paper shows is that varying the particular dietary contents is not what counts, but getting caloric count down is where we need to be," Dr. Hirsch told Medscape Medical News. In addition, he said, the study shows that "a low-protein diet has no place in the treatment or production of obesity."

Dr. Bray reported that he has been a consultant to Abbott Laboratories and Takeda Global Research Institute; is an advisor to Medifast, Herbalife, and Global Direction in Medicine; and has received royalties for the Handbook of Obesity. Corby K. Martin, MD, also of the Pennington Biomedical Research Center, reported consultancies with Bristol-Myers Squibb, Eli Lily, Elcelyx, Merck, and Philips and has received compensation from International Life Sciences Institute for manuscript preparation, travel expenses from Catapult Health, Domain & Associates, and the University of Tennessee. The other authors have disclosed no relevant financial relationships. Dr. Heber has reported that he is a counselor of the Obesity Society for Clinical Research; an advisor to POM Wonderful, Herbalife, and McCormick Spice; and has received book royalties for What Color Is Your Diet. Dr. Li has disclosed no relevant financial relationships. Dr. Pi-Sunyer has reported serving on the Scientific Advisory Board for Weight Watchers, Orexigen, Vivus, and Novo Nordisk. Dr. Hirsch has disclosed no relevant financial relationships.

JAMA. 2012;307:47-55.

    
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