Time restricted eating, eating behaviors, and cardiometabolic risk in emerging adults

Abstract

Emerging adulthood (ages 18-29 years) is a key life stage for cardiovascular disease prevention. Time restricted eating (TRE) interventions shorten the daily eating window, or length of time in the day from first to last caloric consumption. TRE has beneficial effects on cardiovascular risk factors, including components of metabolic syndrome such as blood pressure, blood glucose, and triglycerides. These benefits occur without placing limits on caloric intake or types of foods consumed or requiring weight loss. However, there is limited evidence on the extent to which the fasting that is inherent to TRE may elicit feelings of restraint and subsequent disinhibited eating (i.e. overeating in response to external food cues or emotional states), especially in emerging adults who are vulnerable to maladaptive eating behaviors. It is imperative to understand the relationship between TRE, restraint and disinhibition in emerging adults, as restraint and disinhibition increase risk for disordered eating and cardiovascular disease. This dissertation explored the relationship between TRE, eating behaviors, and risk factors for adverse cardiometabolic health in emerging adults through three studies. ☐ In the first study, the eating patterns of emerging adults and the relationship between eating window length, night eating, and metabolic syndrome risk were examined using National Health and Nutrition Examination Survey 2017-2020 pre-pandemic data. Mean eating window length was 10.9 (SE: 0.1) hours; 34.7% of emerging adults had an eating window ≥ 12 hours. Median percent of calories consumed after 8pm was 18.8% (SE: 0.8); 11.2% of emerging adults consumed ≥25% of calories after dinner. Multiple linear regression models showed that longer eating windows were associated with lower metabolic syndrome risk in males (β=-0.06, p=0.0008) and in females who ate a greater proportion of calories after dinner (p=0.008). This study suggested that eating window timing may influence metabolic syndrome risk. ☐ The second study was a single-arm trial that assessed the impact of a 4-week TRE intervention in 36 emerging adult women (median age 22.0, IQR 20.75 – 24.25) with moderate-high dietary restraint and baseline eating windows ≥12 hours. Participants’ eating windows were reduced to 10 hours per day and ended by 8pm. Participants experienced significantly decreased emotional eating (Dutch Eating Behavior Questionnaire emotional eating subscale, p=0.009, Cohen’s d=-0.470), caloric intake (p=0.006, Cohen’s d=-0.617), body weight (p<0.001, Cohen’s d=-0.649), and visceral fat (p=0.026, Cohen’s d=-0.452) between baseline and the end of the TRE intervention. Ecological momentary assessment surveys were administered 5 times per day to assess whether participants had recently eaten and why. The odds of reporting eating without hunger were significantly lower during TRE than baseline (OR for week 1 compared to baseline: 0.37, 95% CI: 0.24-0.59, p<0.001, OR for week 4 compared to baseline: 0.41, 95% CI: 0.26-0.65, p<0.001). Emerging adult women experienced positive changes in eating behaviors and cardiovascular risk factors with a relatively short intervention and modest eating window reduction. ☐ In the third and final study, semi-structured qualitative interviews were conducted 4 weeks after the completion of the TRE intervention (n=19, 13 moderately restrained eaters, 6 highly restrained eaters). The study’s aims were to understand participants’ experiences following the TRE intervention and to explore the extent to which restraint theory explained their experiences. Restraint theory posits that restricting intake will cause individuals with high levels of dietary restraint to experience disinhibition. Deductive qualitative analysis was used to analyze transcripts and examine restraint theory constructs and thematic analysis was used to inductively develop additional themes. Four themes were identified: (1) highly restrained eaters experience disinhibition or loss of control after a restriction is imposed on eating, (2) self-directed changes in eating and daily routines necessary to minimize hunger, (3) increased intentional eating, reduced “food noise”, and (4) TRE is feasible short term, but may not be sustainable. Findings supported restraint theory: highly restrained eaters were the only participants to experience disinhibition and loss of control eating during the study. ☐ In summary, results from this dissertation provide evidence that the timing of meal intake and eating window placement are important considerations for cardiometabolic health. Emerging adult women experienced benefits after 4 weeks of TRE intervention, including reduced emotional eating and reduced eating in the absence of hunger. However, qualitative data suggested that highly restrained eaters experienced disinhibition and loss of control eating during the study, indicating that alternative approaches to improving health may be warranted in this group. Future work should continue to explore ideal eating window length, eating window placement within the day, and moderators of response to TRE interventions.