Increased odds of having the metabolic syndrome with greater fat‐free mass: counterintuitive results from the National Health and Nutrition Examination Survey database

Abstract

Background It is well established that body composition influences metabolic health, but emerging data are conflicting with the largely purported idea that a large fat‐free mass (FFM) has a protective effect on health. A potential explanation for these discrepancies is the way FFM is represented. The first objective is to determine the association between the metabolic syndrome (MetS) and FFM when the latter was represented in three different ways: 1—absolute FFM; 2—relative to squared height (FFMi); and 3—relative to body weight (FFM%). The second objective is to assess the impact of FFM on the relative risk of having the MetS after taking fat mass, physical activity, and sociodemographic variables into account. Methods A total of 5274 individuals from the National Health and Nutrition Examination Survey database were studied. Age‐specific and sex‐specific quartiles of the three representations of FFM were defined, and the prevalence of MetS was determined in each of them. Quartiles of FFMi (kg/m2) were used to calculate the odds ratios of having the MetS independently of FM, physical activity levels, and sociodemographic variables. Results The prevalence of MetS decreased with increasing quartiles of whole‐body FFM% (Q1: 40%; Q4: 10%) but grew with increasing quartiles of absolute FFM (Q1: 13%; Q4: 40%) and FFMi (Q1: 10%; Q4: 44%). Similar results were observed for appendicular and truncal FFM. The odds ratios of having the MetS, independently of fat mass, physical activity, and sociodemographic variables, were significantly greater in the fourth quartile of FFMi when compared with the first quartiles of each specific subgroup [Q4 vs. Q1: younger men: 4.16 (1.99–8.68); younger women: 5.74 (2.46–13.39); older men: 1.98 (1.22–3.22); older women: 2.88 (1.69–4.90); all P ≤ 0.01]. Conclusions These results support the notion that the representation of FFM significantly influences its association with MetS and that a larger FFM, whether absolute or relative to height, is associated with alterations in cardiometabolic health.

Impact of low relative skeletal muscle mass and power on the development of metabolic syndrome in Japanese women: a 7-year prospective study

“…On the contrary, high ALM/height 2 or high absolute ALM had significantly higher incident of MetS during the follow-up period. This is consistent with the recent crosssectional study [24] and previous studies [7][8][9][10][11][12][13][14]. It is because the people who have higher body weight tend have higher muscle mass.…”

Association between skeletal muscle mass or percent body fat and metabolic syndrome development in Japanese women: A 7-year prospective study

“…The results of the current study are consistent with these reports, and this is the first prospective study to examine the association between low ALM/Wt and MetS development, to the best of our knowledge. In contrast, high ALM/Ht 2 showed significantly higher MetS incidence during the follow-up period, which is consistent with a recent cross-sectional study [ 36 ] and previous studies [ 10 – 17 ]. However, most of the previous studies did not take into account the effect of fat mass or percent body fat on the association between ALM and MetS development.…”

“…However, people with a higher body weight exhibit higher muscle mass and strength, and previous studies indicated that the normalization of muscle mass or strength by body weight or body mass index (BMI) is needed to see the association between SMM or strength and MetS [ 10 – 17 ]. Previous cross-sectional studies indicated that relative ALM per kg weight (ALM/Wt) or BMI (ALM/BMI) are inversely associated with MetS [ 10 – 17 ], but relative ALM (or fat-free mass) per squared height (ALM/Ht 2 ) or absolute ALM (or fat-free mass) are positively associated with MetS [ 18 – 21 ].…”

Conflicting Associations among Bioelectrical Impedance and Cardiometabolic Health Parameters in Young White and Black Adults

“…Specifically, it is a common misconception that increased weight status is predominately attributable to FM accumulation. To the contrary, within the framework of the obesity epidemic, absolute FFM and FM typically increase in tandem resulting in cardiometabolic abnormalities regardless of total FFM (48), evident by studies reporting an increased risk of MetS with greater FFM (49). As such, it is important to consider these associations in the appropriate context given that they may be distorted by whole body hypertrophy, particularly for young adults.…”