Circadian rhythms - exercise & meal timing

Two studies on exercise and a review on meal timing.

Single-session exercise studies show better performance in the afternoon, although this is trainable - consistent AM training improves performance in the AM and PM whereas consistent PM training does not improve AM performance. 

Chronotype effects? Circadian rhythms?



But that's neither here nor there. Exercise is better than no exercise, and if you have the luxury to choose, evidence favors AM. 

Comparison between the effect of 6 weeks of morning or evening aerobic exercise on appetite and anthropometric indices: a randomized controlled trial (Alizadeh et al., 2017).

Good study - main outcomes were body weight, appetite, and ad lib food intake. 

Exercise doesn't burn a whole lot of calories but it's very good for you. A goal of this study was to see if exercise timing influenced appetite and ad lib food intake, which have a greater role in regulating body composition.

The exercise intervention was modest, ~30 minutes of cardio in the morning or afternoon. Main findings: significantly greater reduction in body weight, BMI, waist circumference, abdominal circumference, and abdominal skin fold thickness in the morning exercise group. 

The morning group also spontaneously ate less throughout the day despite no difference in appetite/hunger scores or exercise intensity between the groups. Boom.



The feasibility and acceptability of morning versus evening exercise for overweight and obese adults: a randomized controlled trial (Brooker et al., 2019)

A better study - morning exercise vs. evening exercise vs. A CONTROL GROUP.

Main findings: most outcome measures (perceived enjoyment, exercise intensity, time spent in moderate & vigorous intensity) were similar between groups but all measures slightly favored AM exercise. 

Reduction in body fat was better in the AM group and RMR took a slightly greater drop in the PM group.

Again, exercise is better than no exercise (the more important variable), but evidence favors AM.


Timing of breakfast, lunch, and dinner. Effects on obesity and Metabolic Risk (Lopez-Minguez et al., 2019)

"eating is fundamental to survival"

"food intake is a major external synchronizer of peripheral clocks"

"the obesogenic effect of eating late" !

"unusual eating time can produce a disruption in the circadian system that might lead to unhealthy consequences"

This research started out with the observations that late eaters tended to be heavier than early eaters. It was followed up by randomized intervention trials (eg., Jakubowicz, Jacobs & Hirsch, etc.) which showed greater weight loss in early eaters than late eaters in body ad lib and isocaloric studies. Not magic -- the thermic effect of feeding is lower after evening meals, glucose tolerance is reduced at night, and adipose tissue is more prone to store excess energy as fat later in the day. 

This review article includes a huge table of all the studies on this - check it out if you're interested. Randomized crossover intervention trials, and even observational studies across countries who tend to eat earlier or later. Tl;dr: those late-dinner countries aren't always leaner than early-dinner countries.

Some genes might be involved: PLIN1 and MTNR1B.

A lot of talk about chronotypes although I don't really think there are different chronotypes within species. Humans are diurnal; mice are nocturnal. Humans with alleged "late chronotypes" consistently show poorer health across studies... so they may be "owls," but mice that play during the day are more likely to be predated. So there's that.

From the eTRF studies, there was a spectrum in the interpretation of "late-eating" -- it was basically, the bigger your last meal, the earlier it should be.

Does AM exercise and skewing kcals earlier in the day work for you? Will you try it?

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calories proper

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