Changes in pedometer-measured physical activity are associated with weight loss and changes in body composition and fat distribution in response to reduced-energy diet interventions: The POUNDS Lost trial

Is There an Ideal Diet? Some Insights from the POUNDS Lost Study

Diets for weight loss have a long history but an ideal one has not yet been clearly identified. To compare low-fat and lower carbohydrate diets, we designed The Preventing Overweight by Novel Dietary Strategies (POUNDS) Lost study. This is a 2 × 2 factorial study with diets of 20% or 40% fat and 15% or 25% protein with a graded carbohydrate intake of 35, 45, 55 and 65%. Weight loss, overall, was modest at nearly 6% with all four diets, and no significant dietary difference. The variability in weight loss in each diet group was significant, ranging from greater than 20% to a small weight gain. Studies of genetic variations in relation to weight loss showed that the diet that was selected could significantly affect weight loss, emphasizing that there is no ideal diet and more than one diet can be used to treat obesity. Weight loss was also influenced by the level of baseline triiodothyronine or thyroxine, and baseline carbohydrate and insulin resistance. Achieving a stable Health Eating Food Diversity Index, eating more protein, eating more fiber, engaging in more physical activity, sleeping better and eating less ultra-processed foods were beneficial strategies for weight loss in this trial. Although there is no "ideal diet", both the DASH diet and the Mediterranean diet have clinical trials showing their significant benefit for cardiovascular risk factors. Finally, the lesson of the "Last Chance Diet", which recommended a diet with protein from gelatin, proved that some diets could be hazardous.

Circulating MicroRNA-19 and cardiovascular risk reduction in response to weight-loss diets

OBJECTIVE

MicroRNA-19 (miR-19) plays a critical role in cardiac development and cardiovascular disease (CVD). We examined whether change in circulating miR-19 was associated with change in CVD risk during weight loss.

METHODS

This study included 509 participants with overweight or obesity from the 24-month weight-loss diet intervention study (the POUNDS Lost trial) and with available data on circulating miR-19a-3p and miR-19b-3p at baseline and 6 months. The primary outcome for this analysis was the change in atherosclerotic CVD (ASCVD) risk at 6 and 24 months, which estimates the 10-year probability of hard ASCVD events. Secondary outcomes were the changes in ASCVD risk score components.

RESULTS

Circulating miR-19a-3p and miR-19b-3p levels significantly decreased during the initial 6-month dietary intervention period (P = 0.008, 0.0004, respectively). We found that a greater decrease in miR-19a-3p or miR-19b-3p was related to a greater reduction in ASCVD risk (β[SE] = 0.33 [0.13], P = 0.01 for miR-19a-3p; β[SE] = 0.3 [0.12], P = 0.017 for miR-19b-3p) over 6 months, independent of concurrent weight loss. Moreover, we found significant interactions between change in miR-19 and sleep disturbance on change in ASCVD risk over 24 months of intervention (P interaction = 0.01 and 0.008 for miR-19a-3p and miR-19b-3p, respectively). Participants with a greater decrease in miR-19 without sleep disturbance had a greater reduction of ASCVD risk than those with slight/moderate/great amounts of sleep disturbance. In addition, change in physical activity significantly modified the associations between change in miR-19 and change in ASCVD risk over 24 months (P interaction = 0.006 and 0.004 for miR-19a-3p and miR-19b-3p, respectively). A greater decrease in miR-19 was significantly associated with a greater reduction in ASCVD risk among participants with an increase in physical activity, while non-significant inverse associations were observed among those without an increase in physical activity.

CONCLUSIONS

In conclusion, decreased circulating miR-19 levels during dietary weight-loss interventions were related to a significant reduction in ASCVD risk, and these associations were more evident in people with no sleep disturbance or increase in physical activity.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00072995.

Change analysis for intermediate disease markers in nutritional epidemiology: a causal inference perspective

BACKGROUND

Several approaches are commonly used to estimate the effect of diet on changes of various intermediate disease markers in prospective studies, including "change-score analysis", "concurrent change-change analysis" and "lagged change-change analysis". Although empirical evidence suggests that concurrent change-change analysis is most robust, consistent, and biologically plausible, in-depth dissection and comparison of these approaches from a causal inference perspective is lacking. We intend to explicitly elucidate and compare the underlying causal model, causal estimand and interpretation of these approaches, intuitively illustrate it with directed acyclic graph (DAG), and further clarify strengths and limitations of the recommended concurrent change-change analysis through simulations.

METHODS

Causal model and DAG are deployed to clarify the causal estimand and interpretation of each approach theoretically. Monte Carlo simulation is used to explore the performance of distinct approaches under different extents of time-invariant heterogeneity and the performance of concurrent change-change analysis when its causal identification assumptions are violated.

RESULTS

Concurrent change-change analysis targets the contemporaneous effect of exposure on outcome (measured at the same survey wave), which is more relevant and plausible in studying the associations of diet and intermediate biomarkers in prospective studies, while change-score analysis and lagged change-change analysis target the effect of exposure on outcome after one-period timespan (typically several years). Concurrent change-change analysis always yields unbiased estimates even with severe unobserved time-invariant confounding, while the other two approaches are always biased even without time-invariant heterogeneity. However, concurrent change-change analysis produces almost linearly increasing estimation bias with violation of its causal identification assumptions becoming more serious.

CONCLUSIONS

Concurrent change-change analysis might be the most superior method in studying the diet and intermediate biomarkers in prospective studies, which targets the most plausible estimand and circumvents the bias from unobserved individual heterogeneity. Importantly, careful examination of the vital identification assumptions behind it should be underscored before applying this promising method.

Toward Precision Weight-Loss Dietary Interventions: Findings from the POUNDS Lost Trial

The POUNDS Lost trial is a 2-year clinical trial testing the effects of dietary interventions on weight loss. This study included 811 adults with overweight or obesity who were randomized to one of four diets that contained either 15% or 25% protein and 20% or 40% fat in a 2 × 2 factorial design. By 2 years, participants on average lost from 2.9 to 3.6 kg in body weight in the four intervention arms, while no significant difference was observed across the intervention arms. In POUNDS Lost, we performed a series of ancillary studies to detect intrinsic factors particular to genomic, epigenomic, and metabolomic markers that may modulate changes in weight and other cardiometabolic traits in response to the weight-loss dietary interventions. Genomic variants identified from genome-wide association studies (GWASs) on obesity, type 2 diabetes, glucose and lipid metabolisms, gut microbiome, and dietary intakes have been found to interact with dietary macronutrients (fat, protein, and carbohydrates) in relation to weight loss and changes of body composition and cardiometabolic traits. In addition, we recently investigated epigenomic modifications, particularly blood DNA methylation and circulating microRNAs (miRNAs). We reported DNA methylation levels at NFATC2IP, CPT1A, TXNIP, and LINC00319 were related to weight loss or changes of glucose, lipids, and blood pressure; we also reported thrifty miRNA expression as a significant epigenomic marker related to changes in insulin sensitivity and adiposity. Our studies have also highlighted the importance of temporal changes in novel metabolomic signatures for gut microbiota, bile acids, and amino acids as predictors for achievement of successful weight loss outcomes. Moreover, our studies indicate that biochemical, behavioral, and psychosocial factors such as physical activity, sleep disturbance, and appetite may also modulate metabolic changes during dietary interventions. This review summarized our major findings in the POUNDS Lost trial, which provided preliminary evidence supporting the development of precision diet interventions for obesity management.