Ectopic lipid deposition in overweight women: an MRS study of the liver

Abstract

Background: Ectopic lipid deposition in the liver may be an important factor in adverse metabolic health and development of T2D. Although obesity is a major risk factor for ectopic lipid deposition, not all overweight or obese individuals have ectopic fat. Aim: To determine whether there is a risk phenotype that is associated with ectopic fat deposition in the liver, in normal weight and overweight Caucasian women who were enrolled in a clinical study conducted as part of the Peak Nutrition for Metabolic Health (PANaMAH) National Science Challenge program in New Zealand. Methods: A total of 94 Caucasian women completed: anthropometric measurements including body weight, height, waist circumference, and hip circumference; information on alcohol consumption; blood pressure recordings; blood sample collection; and (n=93) dual-energy X-ray absorptiometry (DEXA) body composition assessment. A sub-cohort of women (n=34) underwent liver magnetic resonance spectroscopy (MRS) scans to determine liver fat percentage and (n=32) completed physical fitness testing by the YMCA Cycle Ergometer test, to estimate VO2max. Results: In women who completed a MRS scan, liver fat was strongly correlated with higher systolic blood pressure (SBP) (p< 0.0001) and serum triglycerides (p= 0.0034). Older age (p= 0.0152), higher visceral fat percentage (p= 0.0184), and higher abdominal fat percentage (p= 0.0491) were also strongly associated with liver fat percentage. Women with greater liver fat (>5.56%) were older (55.8 years, p= 0.0298) bigger (BMI 31.2 kg/m2, p= 0.0003), more dysglycaecmic (HbA1c 35.7 mmol/mol, p= 0.0483; FPG 5.5 mmol/L, p= 0.0065), and had higher waist circumference (101.2 cm, p= 0.0009), blood pressure (SBP 132.6 mmHg, p= 0.008; diastolic blood pressure 67.8 mmHg, p= 0.0095), ALP (117.9 U/L, p= 0.0016), serum triglycerides (1.3 mmol/L, p= 0.0153), and body fat stores (total body fat 46.5%, p= 0.001; abdominal fat 53.7% of abdominal tissue; p= 0.0008; visceral fat 39.4% of abdominal fat, p= 0.0001), compared to women with low liver fat (<5.56%). Conclusion: The risk phenotype associated with ectopic lipid deposition in the liver in normal weight and overweight Caucasian women includes: higher systolic blood pressure, serum triglycerides, older age, visceral fat percentage, and abdominal fat percentage. BMI, HbA1c, FPG, waist circumference and ALP were also significantly higher in women with greater liver fat (>5.56%),therefore are also important in the risk phenotype. While cardiorespiratory fitness was not directly associated with liver fat, the strong association of high cardiorespiratory fitness with other risk factors of adverse metabolic risk, emphasise it may play a role in the risk phenotype for ectopic lipid deposition in the liver.