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Time Restricted Dieting: Maybe Not the Answer

Reference

JAMA Intern Med. Published online August 8, 2022. doi:10.1001/jamainternmed.2022.3050

Study Summary

14 week randomized controlled trial to determine if eating a calorie restricted diet in an 8 hour window between 7 AM to 3 PM vs. just the 500 calorie restriction and eating over a 12 hour window would improve weight loss.

The intervention found more effective weight loss (−2.3 kg; 95% CI, −3.7 to −0.9 kg; P = .002) but NOT loss of body fat (−1.4 kg; 95% CI, −2.9 to 0.2 kg; P = .09).

It also had minimal effects on diastolic blood pressure (−4 mm Hg; 95% CI, −8 to 0 mm Hg; P = .04), mood, fatigue, and vigor.

In a secondary analysis of those who maintained the time restriction at 14 weeks (so called completers) intervention produced greater weight loss (−2.3 kg; 95% CI, −3.9 to −0.7 kg; P = .006), body fat loss (−1.8 kg; 95% CI, −3.6 to 0.0 kg; P = .047), and trunk fat loss (−1.2 kg; 95% CI, −2.2 to −0.1 kg).

Conclusions

Time restricted eating for 14 weeks may provide a weight loss as well as a reduction in fat mass.

Discussion

There is very little human data on the benefit of time restricted eating, aka intermittent fasting, despite it being studied for over 35 years. Most of the data is lab animal based, where stressors and commonly available foods are not an option. They seem effective in the animal lab, but in the few studies in humans, short term benefits have been seen, but often the inability to maintain the time limit leads to no clinical benefit.

One possible exception is the “5:2” diet, where the patient is asked to fast on just two separate days, and the removal of food restrictions on non-fasting days. The patient may choose any two non-consecutive days each week to limit intake to 500 Kcal/day. This flexibility allows for events and special meals to be accommodated. And the overbearing pressure to quell cravings is for just 2 days a week.

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