不论蛋白质、脂肪或碳水化合物比率 过多热量是肥胖的主因


  【24drs.com】1月3日JAMA期刊的新研究认为,不论蛋白质、脂肪和碳水化合物的特定比率,摄食过量是肥胖的重要原因,也是抑制的关键;此外,低蛋白质饮食(约5%)特别有危险,导致有保护力的净体重降低。
  
  Pennington生物医学研究中心的George Bray医师等人写道,这篇研究的主要结果是,热量比蛋白质更重要,吃过多热量和体脂肪增加有关。再者,作者写道,与蛋白质占饮食热量15%和25%相比,蛋白质仅提供5%的饮食热量,其代谢差异为较高的能量消耗比较不会增加体重。
  
  故意给25名健康年轻男性和女性每天增加1000卡热量、超过56天;过量饮食是根据开始时的体重稳定评估而定。研究设计为单盲、随机控制试验,病患在2005年6月至2007年10月住进代谢病房。
  
  先给予病患13-25天的稳定体重饮食,之后随机分组为:低蛋白质组(占总量5%)、正常蛋白质组(总量15%)与高蛋白质组(总量25%)。与体重稳定治疗相比,增加的蛋白质多提供了40%的热量,相当于每天954大卡(95%信心区间[CI],每天884 – 1022大卡)。主要结果是使用双能量X光吸收仪评估身体组成;休息时的能量消耗;总能量消耗。
  
  根据该研究,单纯摄取过多热量导致体脂肪较高。就降低净体重而言,与正常和高蛋白质饮食相比,低蛋白质饮食证明有害,特别的是,该研究发现,相较于正常蛋白质组(6.05公斤;95% CI,4.84 - 7.26公斤)或高蛋白质组(6.51公斤;95% CI,5.23 - 7.79公斤;P = .002),低蛋白质治疗组的体重增加程度显著较少(3.16公斤;95% CI,1.88 - 4.44公斤)。
  
  当评估这三组的体脂肪时,研究者发现,增加的情况相同,与蛋白质无关。低蛋白质组并未增加休息时的能量消耗、总能量消耗、或净体重,但是,正常蛋白质或高蛋白质组则有(休息时能量消耗:正常蛋白质饮食-每天160大卡[95% CI,102 – 218大卡/天]、高蛋白质组-每天227大卡[95% CI,165 - 289大卡/天];净体重:正常蛋白质饮食- 2.87公斤[95% CI,2.11 - 3.62公斤]、高蛋白质组- 3.18公斤[95% CI,2.37 - 3.98公斤])。
  
  编辑评论中,加州大学洛杉矶分校的David Heber博士和Zhaoping Li博士表示,这篇研究强调蛋白质对减重介入的重要性。Heber博士和Li博士写道,研究强度之一是,它评估了脂肪累积,不只是整体体重增加和身体质量指数,因为他们认为这些可能会产生误导。
  
  他们写道,医师应考虑评估病患的整体脂肪量,而不只是测量体重或身体质量指数,且要注意累积过多脂肪可能引起的并发症。肥胖治疗的目标应包括减少脂肪,而不只是减重,且要更加了解营养科学。
  
  哥伦比亚大学医学教授、纽约市圣路加罗斯福医院肥胖研究中心主任、未参与该研究的Xavier Pi-Sunyer医师表示,他并不认为脂肪组成可以取代身体质量指数和体重,应该是「吃太多引起体重增加」。
  
  他指出,该研究对肥胖引起的公卫影响有限,我们正致力于减少热量,而不是过量,此外,多数美国人有12%-15%的热量来自蛋白质,所以他不担心足量蛋白质的压力。
  
  不过,人类行为与代谢研究中心负责人、名誉教授、纽约Rockefeller大学名誉外科主任Jules Hirsch医师表示,我们试过多种热量组合,都没有显示出因果关系,只有过多热量显示与引起肥胖有关,这也可用来设计有效的介入方式。
  
  Hirsch医师表示,饮食内容的变化并不是最重要的,我们需要的是降低热量摄取,该研究显示,低蛋白质饮食对于治疗或造成肥胖无关。
  
  资料来源: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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