JAMA Intern Med：红肉摄入量增多 2型糖尿病风险增加？

　　美国和加拿大联合研究表明，红肉摄入量增多与随后2型糖尿病（T2DM）风险增加相关，且这一相关性受到体重影响。限制红肉摄入量有利于预防T2DM。论文6月17日在线发表于《美国医学会杂志·内科学》（JAMA Intern Med）。

　　该研究随访近15万人。使用食物频率问卷评估饮食情况，并每4年评估一次。校正年龄、家族史、种族、婚姻状况，初始红肉摄入量、吸烟状态、其他生活方式因素（体力活动、饮酒、总能量摄入、饮食质量）的初始状态和变化后，通过时间依赖的考克斯比例风险回归模型计算风险比。荟萃分析汇合各队列结果。主要终点为补充问卷证实T2DM发生。

　　结果为，在1965824人-年的随访期间，共发生7540例T2DM。多变量校正模型分析表明，4年中红肉摄入量增多与随后4年中T2DM风险增加有关。与红肉摄入量无变化的参照组相比，红肉摄入量增多超过0.50 份/天（1份=85.05 g）与随后4年T2DM风险增加48%[汇合风险比（HR）=1.48]相关，进一步校正初始体质指数和随访期间的体重增加后，这一相关性略有减弱（汇合HR=1.30）。从基线时起至随访的第一个4年，红肉摄入量减少超过0.50 份/天与随后整个随访期间T2DM风险降低14%（汇合HR=0.86）相关。

　　■ 同期述评

　　蛋白质vs脂肪 谁是增加2型糖尿病风险的“真凶”？

　　美国杜克大学医学部 埃文斯（Evans）

　　上述研究表明，所谓“红肉”的摄入量与T2DM的风险增加相关，为制定降低T2DM风险的策略提供了有价值的数据。然而，“红肉”这一分类描述并不准确，其作为一类食品的研究价值小且可能产生误导。

　　尚无证据表明，肉中蛋白质的量或类型可影响胰岛素抵抗或T2DM风险。摄入肉类中对此风险影响最大的或许不是蛋白质，而是饱和脂肪酸。

　　参与构成T2DM病因的遗传与生活方式因素间的相互作用十分复杂，目前仍不明确。与T2DM风险相关的主要因素是体力活动水平、机体肥胖程度、体脂分布和饮食。研究表明，坚果或鱼类替代红肉可降低T2DM风险，提示所摄入的脂肪酸的组成和量对胰岛素抵抗和T2DM的形成具有重要影响。

　　富含肌红蛋白和血红蛋白的肉类中含很多重要营养素，其一便是血红素铁，这是食物中生物利用度最高的铁。少吃红肉可能有助于减少T2DM，但多学科证据支持摄入低总脂肪和饱和脂肪的优质蛋白质。这尤其适用于对饮食蛋白质需求高、能量需求少的老年人。因此，建议摄入脂肪含量少的红肉，以及鱼类、家禽和低脂奶制品。因为问题的关键并不是蛋白质（或肉类）的类型，而是脂肪类型。

Changes in Red Meat Consumption and Subsequent Risk of Type 2 Diabetes Mellitus: Three Cohorts of US Men and Women.
IMPORTANCE
Red meat consumption has been consistently associated with an increased risk of type 2 diabetes mellitus (T2DM). However, whether changes in red meat intake are related to subsequent T2DM risk remains unknown.
OBJECTIVE
To evaluate the association between changes in red meat consumption during a 4-year period and subsequent 4-year risk of T2DM in US adults.
DESIGN AND SETTING
Three prospective cohort studies in US men and women.
PARTICIPANTS
We followed up 26 357 men in the Health Professionals Follow-up Study (1986-2006), 48 709 women in the Nurses' Health Study (1986-2006), and 74 077 women in the Nurses' Health Study II (1991-2007). Diet was assessed by validated food frequency questionnaires and updated every 4 years. Time-dependent Cox proportional hazards regression models were used to calculate hazard ratios with adjustment for age, family history, race, marital status, initial red meat consumption, smoking status, and initial and changes in other lifestyle factors (physical activity, alcohol intake, total energy intake, and diet quality). Results across cohorts were pooled by an inverse variance-weighted, fixed-effect meta-analysis.
MAIN OUTCOMES AND MEASURES
Incident T2DM cases validated by supplementary questionnaires.
RESULTS
During 1 965 824 person-years of follow-up, we documented 7540 incident T2DM cases. In the multivariate-adjusted models, increasing red meat intake during a 4-year interval was associated with an elevated risk of T2DM during the subsequent 4 years in each cohort (all P < .001 for trend). Compared with the reference group of no change in red meat intake, increasing red meat intake of more than 0.50 servings per day was associated with a 48% (pooled hazard ratio, 1.48; 95% CI, 1.37-1.59) elevated risk in the subsequent 4-year period, and the association was modestly attenuated after further adjustment for initial body mass index and concurrent weight gain (1.30; 95% CI, 1.21-1.41). Reducing red meat consumption by more than 0.50 servings per day from baseline to the first 4 years of follow-up was associated with a 14% (pooled hazard ratio, 0.86; 95% CI, 0.80-0.93) lower risk during the subsequent entire follow-up through 2006 or 2007.
CONCLUSIONS AND RELEVANCE
Increasing red meat consumption over time is associated with an elevated subsequent risk of T2DM, and the association is partly mediated by body weight. Our results add further evidence that limiting red meat consumption over time confers benefits for T2DM prevention.