A novel way to cut calories?
The Australian authors say there is growing interest in extending the established health benefits of calorie restriction through new approaches such as timing of meals and prolonged fasting, with IF – defined as fasting interspersed with days of ad libitum eating – gaining in popularity as an alternative to simple calorie restriction.
Time-restricted eating, which emphasizes shorter daily eating windows in alignment with circadian rhythms, has also become popular in recent years, although the authors acknowledge that current evidence suggests any benefits over calorie restriction alone in terms of body composition, blood lipids, or glucose parameters are small.
To examine the combination of IF plus early time-restricted eating, in the DIRECT trial, the team recruited individuals aged 35-75 years who had a score of at least 12 on the Australian Type 2 Diabetes Risk Assessment Tool but did not have a diagnosis of diabetes and had stable weight for more than 6 months prior to study entry.
The participants were randomized to one of three groups:
- IF plus early time-restricted eating, which allowed consumption of 30% of calculated baseline energy requirements between 8:00 a.m. and midday, followed by a 20-hour fast from midday on 3 nonconsecutive days per week. They consumed their regular diet on nonfasting days.
- Calorie restriction, where they consumed 70% of daily calculated baseline energy requirements each day and were given rotating menu plans, but no specific mealtimes.
- Standard care, where they were given a booklet on current guidelines, with no counseling or meal replacement.
There were clinic visits every 2 weeks for the first 6 months of follow-up, and then monthly visits for 12 months. The two intervention groups had one-on-one diet counseling for the first 6 months. All groups were instructed to maintain their usual physical activity levels.
A total of 209 individuals were enrolled between Sept. 26, 2018, and May 4, 2020. Their mean age was 58 years, and 57% were women. Mean body mass index was 34.8 kg/m2.
In all, 40.7% of participants were allocated to IF plus early time-restricted eating, 39.7% to calorie restriction, and the remaining 19.6% to standard care.
The results showed that IF plus early time-restricted eating was associated with a significantly greater improvement in the primary outcome of postprandial glucose area under the curve (AUC) at month 6 compared with calorie restriction, at –10.1 mg/dL/min versus –3.6 mg/dL/min (P = .03).
“To our knowledge, no [prior] studies have been powered for postprandial assessments of glycemia, which are better indicators of diabetes risk than fasting assessment,” the authors underlined.
IF plus early time-restricted eating was also associated with greater reductions in postprandial insulin AUC versus calorie restriction at 6 months (P = .04). However, the differences between the IF plus early time-restricted eating and calorie restriction groups for postmeal insulin did not remain significant at 18 months of follow-up.
Both IF plus early time-restricted eating and calorie restriction were associated with greater reductions in A1c levels at 6 months versus standard care, but there was no significant difference between the two active interventions (P = .46).
Both interventions were also associated with improvements in markers of cardiovascular risk versus standard care, such as systolic blood pressure at 2 months, diastolic blood pressure at 6 months, and fasting triglycerides at both time points, with no significant differences between the two intervention groups.
IF plus early time-restricted eating and calorie restriction were also both associated with greater reductions in BMI and fat mass in the first 6 months, as well as in waist circumference.