Purpose of Review

Individuals with metabolically unhealthy normal weight (MUNW) have an adverse cardiometabolic risk factor profile in the absence of excess body weight, and increased risk for diabetes and heart disease. We critically review some physiological traits and lifestyle characteristics of the MUNW phenotype.

Recent Findings

The prevalence of MUNW varies considerably around the world and among ethnicities, partly because of different definitions; on average, this phenotype affects about ~ 30% of normal weight persons globally. Most studies have recruited MUNW subjects who, although within the normal weight range, are significantly “more obese” than their metabolically healthy lean peers (greater body mass index or total body fat); hence one cannot ascertain whether observed differences are true traits of the MUNW phenotype of simply secondary to greater relative adiposity within the normal range. Carefully matched studies have indicated that MUNW can exist in the absence of excess total body fat. These subjects have a preferential accumulation of fat in the upper body (abdominal subcutaneous and visceral adipose tissues) and the liver, but not skeletal muscle; perhaps surprisingly, this predominantly “android” fat distribution does not translate into increased waist circumference. The MUNW phenotype is associated with lower aerobic fitness and muscle mass and strength, but whether this is simply due to inadequate regular physical activity is not entirely clear. Likewise, no consistent associations have been found between any dietary factors and the development of MUNW phenotype, but diet-induced modest weight loss facilitates its resolution.

Summary

Delineating the mechanisms leading to metabolic dysfunction in the absence of increased body weight and body fat will likely reveal important targets for improving metabolic health and eventually for reducing the burden of cardiometabolic disease, not only in individuals with normal body weight but also in people with obesity.

中文翻译：

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肥胖症患者体内代谢功能障碍的生理和生活方式特征。

审查目的

正常体重代谢不健康（MUNW）的人在没有过量体重的情况下，心脏代谢风险因素不利，并且患糖尿病和心脏病的风险增加。我们批判性地回顾了MUNW表型的一些生理特征和生活方式特征。

最近的发现

在世界各地和不同种族之间，MUNW的患病率差异很大，部分原因是定义不同；平均而言，该表型影响全球约30％的体重正常的人。大多数研究都招募了MUNW受试者，这些受试者虽然在正常体重范围内，但比其代谢健康的瘦削同龄人（更大的体重指数或总脂肪）明显“肥胖”。因此，无法确定观察到的差异是否是正常范围内相对于较大肥胖的继发性MUNW表型的真实特征。仔细匹配的研究表明，MUNW可以在没有过多的体内总脂肪的情况下存在。这些受试者在上半身（腹部皮下和内脏脂肪组织）和肝脏中有优先的脂肪积累，但骨骼肌中没有。也许令人惊讶的是，这种主要的“人造”脂肪分布并没有转化为腰围的增加。MUNW表型与较低的有氧适应度，肌肉质量和强度有关，但是尚不清楚这是否仅是由于日常体育活动不足引起的。同样，在任何饮食因素与MUNW表型的发展之间也没有发现一致的关联，但是饮食引起的适度的体重减轻有助于其解决。

概要

在不增加体重和体脂的情况下描述导致代谢功能障碍的机制，可能会揭示出重要的目标，不仅对于体重正常的人，而且对于肥胖的人，改善代谢健康并最终减轻心脏代谢疾病的负担。