⏪Rewind: Does meal timing matter for weight loss? Original paper

Although total calorie intake relative to energy expenditure is the most important factor for losing weight, some evidence suggests that the timing of food intake has meaningful health effects. Specifically, some studies suggest that early time-restricted eating, or restricting energy intake to the morning and afternoon, may improve insulin sensitivity relative to restricting energy intake to the afternoon and evening. However, the role of food timing on weight loss outcomes is still unclear.

This secondary analysis of a previous randomized controlled trial^[1] assessed how the timing of energy intake throughout the day affected dietary adherence and weight loss outcomes among participants in a weight loss program. In the original study, 188 healthy participants with a BMI of 22–27.9 reduced their calorie intake by 25% (the CR group) or maintained their habitual intake (the control group) for two years. The participants in the CR group were instructed to monitor their calorie intake daily. They were also encouraged to engage in 30 minutes per day of moderate-intensity physical activity for at least five days per week. No instruction was provided for when to eat.

The investigators assessed the following variables at baseline, 12 months, and 24 months, with additional assessments for the CR group at 6 and 18 months:

• Percent weight change
• Energy intake, obtained using 6-day food records
• Mean meal shift: a measure of the irregularity of a participant’s meal times
• 95% eating interval: the time period in which the participants ate 95% of their daily calories
• Time to 50% of calories: the time point at which a participant ate half of their daily calories
• Percent calorie restriction (percent CR): a measure of percentage of CR relative to baseline intake, as assessed using doubly labeled water (energy expenditure) and DXA (changes in body energy stores to obtain a true measure of energy intake)

As expected, calorie restriction was the primary driver of weight change. However, the participants in the CR group with shorter 95% eating intervals were more likely to have greater calorie restriction and subsequently more weight loss.

In addition, the participants who had an earlier time to 50% of calories lost slightly more weight than those who had a later time to 50% of calories; however, this effect was nonsignificant after accounting for calorie restriction. A lesser shift in the participants’ first and last meals (i.e., more consistent breakfast and dinner times) was correlated with larger weight loss, independent of calorie restriction.