Obesity is associated with insulin resistance but not skeletal muscle dysfunction or all-cause mortality

Abstract

Recent work has found that older adults with obesity and systemic inflammation have associated metabolic dysfunction but do not have associated lower lean mass or strength. However, this lean mass estimate may be inflated with obesity, given that 15 % of adipose tissue is composed of fat-free tissue. The primary purpose of this study was to investigate, in a nationally representative sample of adults, whether obese adults with chronic systemic inflammation (unhealthy) have differences in lean mass, muscle strength, and insulin resistance when compared to normal weight individuals without elevated levels of systemic inflammation (healthy). A secondary objective was to determine whether these potential differences were moderated by physical activity and to determine if these groups had a differential risk for all-cause mortality. Our findings suggests that the unhealthy group was associated with higher upper body lean mass (β = 823; 95 % confidence interval (CI) 637-1010; P < 0.001), lower body lean mass (β = 2724; 95 % CI 2291-3158; P < 0.001), and strength (β = 34.6; 95 % CI 13.5-55.7; P = 0.003) compared to the healthy group despite having systemic inflammation and correcting for fat-free adipose tissue. However, the unhealthy group was associated with insulin resistance (odds ratio (OR) = 16.1; 95 % CI 2.7-96.1; P = 0.005) although this finding was attenuated in those physically active (OR = 8.5; 95 % CI 2.43-30.15; P = 0.003). Despite this metabolic dysfunction, there was no difference in all-cause mortality risk between groups (hazard ratio (HR) = 1.16 (95 % CI 0.69-1.96; P = 0.54)) suggesting that higher amounts of lean mass and strength may be protective of premature mortality.

Calf circumference and risk of cardiovascular disease

“…In previous research, stronger muscle power and higher amounts of lean mass were thought to be protective factors in avoiding premature mortality in older adults with obesity. 13 Generally, our limbs had a higher lean mass compared with other sites on our bodies. The CC, compared with other anthropometric parameters, was observed as being related to muscle mass the most.…”

Association between calf circumference and cardiac metabolic risk factors in middle-aged and elderly women

“…The CC can be used as a screening test for the resting pulse rate, which can be used to prevent cardiovascular events in elderly women [ 21 ]. Another cross-sectional study showed that a low CC may indicate a low risk of cardiovascular disease [ 22 ]. Therefore, the above negative factors related to low CC may increase the risk of cardiovascular events.…”

“…The amount of fast twitch muscle fibres may affect resting systolic or diastolic pressure, pulse pressure, and mean blood pressure [ 21 ]. Another cross-sectional study showed that a large CC might indicate a reduced risk of cardiovascular disease [ 30 ]. The inverse relationship between carotid plaque and an increased CC might also reflect the protective effect of CC and thigh circumference.…”

Molecular studies of exercise, skeletal muscle, and ageing

“… 23 found that CT inter-quartile values for thigh cross-sectional area were 1.7 to 2.1 in 50 year olds with normal weight and homeostatic model assessment insulin resistance (HOMA-IR) but were 1.5 to 2.0 in age-matched obese subjects with insulin resistance – hardly a striking difference. Indeed, after studying 482 adults, Loenneke and Loprinzi found that lean body mass was maintained in the face of insulin resistance and inflammation 24 . Overall, this topic is challenging to address in cross-sectional analyses and using relatively blunt instruments (such as dual-energy X-ray absorptiometry [DXA] or indeed physical activity questionnaires).…”