Relative Effects of Time-Restricted Eating, Energy-Restricted Eating, and Unrestricted Eating on Eating Patterns and Dietary Intake: Results From a Randomized Controlled Trial

BACKGROUND: Time-restricted eating (TRE) may be as effective as an energy-restricted (ER) diet for weight loss. However, little is known about the effects of TRE on eating patterns and dietary intake. OBJECTIVE: The aims of this study were to examine the relative effects of TRE, ER, and unrestricted eating (UE) diets on eating patterns and dietary intake. DESIGN: This study is a secondary analysis of data from a randomized controlled trial carried out between October 2020 and October 2023. Over this period, 88 participants were randomized to a TRE, ER, or UE diet group. PARTICIPANTS/SETTING: Adults with obesity in the Minneapolis-Saint Paul, Minnesota, metropolitan area who completed study baseline and follow-up measures of dietary intake (n = 73). INTERVENTION: The interventions were (1) TRE with an 8-hour self-chosen window with ad libitum diet; (2) ER diet with 15% reduction of energy intake; or (3) UE in which self-monitoring of food intake was encouraged with no specific change to eating recommended. The intervention period was 12 weeks. MAIN OUTCOME MEASURES: Outcomes included meals eaten and intake of vegetables, fruit, dairy, protein foods, grains, energy, added sugars, saturated fat, sodium, dietary fiber, and potassium. STATISTICAL ANALYSES: Multivariate linear regression analyses were carried out to compare the change in food and nutrient intake between experimental groups. Logistic mixed-effects models were constructed to examine the change in meals eaten. RESULTS: The TRE group ate fewer daily meals at end-intervention (-1.1 meals/day; 95% confidence interval [CI], -1.6, -0.7) compared with baseline, whereas the ER and UE groups did not experience a change in eating occasions. Those in the TRE group were less likely to report eating breakfast during end-intervention compared with baseline (odds ratio [OR], 0.13; 95% CI, 0.05, 0.33), whereas no statistically significant change in behavior was identified for the ER (OR, 1.02; 95% CI, 0.41, 2.55) or UE (OR, 0.68; 95% CI, 0.28, 1.68) groups. Between baseline and end-intervention those in the TRE group had a decrease in intake of energy (-469 kcal/day; 95% CI, -681, -257), saturated fat (-8.5 g/day; 95% CI, -12.9, -4.1), potassium (-496 mg/day; 95% CI, -729, -263), and total (-1.7 ounce equivalents/day; 95% CI, -2.9, -0.6) and refined grains (-1.6 ounce equivalents; 95% CI, -2.6, -0.6). These changes were more marked compared with changes in the UE group. There were no statistically significant differences found between those in the TRE and ER groups. CONCLUSIONS: Findings suggest that TRE with an 8-hour window and ad libitum intake may have similar effects on food and nutrient intake as an energy-restricted diet.