Timing of physical activity in relation to liver fat content and insulin resistance.

AIMS/HYPOTHESIS: We hypothesised that the insulin-sensitising effect of physical activity depends on the timing of the activity. Here, we examined cross-sectional associations of breaks in sedentary time and timing of physical activity with liver fat content and insulin resistance in a Dutch cohort. METHODS: In 775 participants of the Netherlands Epidemiology of Obesity (NEO) study, we assessed sedentary time, breaks in sedentary time and different intensities of physical activity using activity sensors, and liver fat content by magnetic resonance spectroscopy (n=256). Participants were categorised as being most active in the morning (06:00-12:00 hours), afternoon (12:00-18:00 hours) or evening (18:00-00:00 hours) or as engaging in moderate-to-vigorous-physical activity (MVPA) evenly distributed throughout the day. Most active in a certain time block was defined as spending the majority (%) of total daily MVPA in that block. We examined associations between sedentary time, breaks and timing of MVPA with liver fat content and HOMA-IR using linear regression analyses, adjusted for demographic and lifestyle factors including total body fat. Associations of timing of MVPA were additionally adjusted for total MVPA. RESULTS: The participants (42% men) had a mean (SD) age of 56 (4) years and a mean (SD) BMI of 26.2 (4.1) kg/m2. Total sedentary time was not associated with liver fat content or insulin resistance, whereas the amount of breaks in sedentary time was associated with higher liver fat content. Total MVPA (-5%/h [95% CI -10%/h, 0%/h]) and timing of MVPA were associated with reduced insulin resistance but not with liver fat content. Compared with participants who had an even distribution of MVPA throughout the day, insulin resistance was similar (-3% [95% CI -25%, 16%]) in those most active in morning, whereas it was reduced in participants who were most active in the afternoon (-18% [95% CI -33%, -2%]) or evening (-25% [95% CI -49%, -4%]). CONCLUSIONS/INTERPRETATION: The number of daily breaks in sedentary time was not associated with lower liver fat content or reduced insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance. Further studies should assess whether timing of physical activity is also important for the occurrence of type 2 diabetes.

Objectively Measured Physical Activity and Body Fatness: Associations with Total Body Fat, Visceral Fat, and Liver Fat.

PURPOSE: It remains unclear to what extent habitual physical activity and sedentary time (ST) are associated with visceral fat and liver fat. We studied the substitution of ST with time spent physically active and total body fat (TBF), visceral adipose tissue (VAT), and hepatic triglyceride content (HTGC) in middle-age men and women. DESIGN: In this cross-sectional analysis of the Netherlands Epidemiology of Obesity study, physical activity was assessed in 228 participants using a combined accelerometer and heart rate monitor. TBF was assessed by the Tanita bioelectrical impedance, VAT by magnetic resonance imaging, and HTGC by proton-MR spectroscopy. Behavioral intensity distribution was categorized as ST, time spent in light physical activity (LPA), and moderate to vigorous physical activity (MVPA). To estimate the effect of replacing 30 min·d-1 of ST with 30 min·d-1 LPA or MVPA, we performed isotemporal substitution analyses, adjusted for sex, age, ethnicity, education, the Dutch Healthy Diet index, and smoking. RESULTS: Included participants (41% men) had a mean ± SD age of 56 ± 6 yr and spent 88 ± 56 min in MVPA and 9.0 ± 2.1 h of ST. Replacing 30 min·d-1 of ST with 30 min of MVPA was associated with 1.3% less TBF (95% confidence interval = -2.0 to -0.7), 7.8 cm2 less VAT (-11.6 to -4.0), and 0.89 times HTGC (0.82-0.97). Replacement with LPA was not associated with TBF (-0.03%; -0.5 to 0.4), VAT (-1.7 cm2; -4.4 to 0.9), or HTGC (0.98 times; 0.92-1.04). CONCLUSIONS: Reallocation of time spent sedentary with time spent in MVPA, but not LPA, was associated with less TBF, visceral fat, and liver fat. These findings contribute to the development of more specified guidelines on ST and physical activity.

Effects of dietary macronutrients on liver fat content in adults: a systematic review and meta-analysis of randomized controlled trials.

Dietary macronutrient composition may affect hepatic liver content and its associated diseases, but the results from human intervention trials have been equivocal or underpowered. We aimed to assess the effects of dietary macronutrient composition on liver fat content by conducting a systematic review and meta-analysis of randomized controlled trials in adults. Four databases (PubMed, Embase, Web of Science, and COCHRANE Library) were systematically searched for trials with isocaloric diets evaluating the effect of dietary macronutrient composition (energy percentages of fat, carbohydrates, and protein, and their specific types) on liver fat content as assessed by magnetic resonance techniques, computed tomography or liver biopsy. Data on change in liver fat content were pooled by random or fixed-effects meta-analyses and expressed as standardized mean difference (SMD). We included 26 randomized controlled trials providing data for 32 comparisons on dietary macronutrient composition. Replacing dietary fat with carbohydrates did not result in changes in liver fat (12 comparisons, SMD 0.01 (95% CI -0.36; 0.37)). Unsaturated fat as compared with saturated fat reduced liver fat content (4 comparisons, SMD -0.80 (95% CI -1.09; -0.51)). Replacing carbohydrates with protein reduced liver fat content (5 comparisons, SMD -0.33 (95% CI -0.54; -0.12)). Our meta-analyses showed that replacing carbohydrates with total fat on liver fat content was not effective, while replacing carbohydrates with proteins and saturated fat with unsaturated fat was. More well-performed and well-described studies on the effect of types of carbohydrates and proteins on liver fat content are needed, especially studies comparing proteins with fats.