Time Restricted Eating (TRE) reduces Calorie absorption?

(Bao et al., 2022)

Time-restricted eating or intermittent fasting gained popularity over recent years as an effective method for weight loss. TRE focuses on the length of the eating window without necessarily altering diet quantity or quality.

Is the effectiveness of TRE just a result of limiting energy intake, or are there other ways it causes a negative energy balance?

In this randomized crossover trial, 12 healthy participants (average age of 24; average BMI of 22; five men, seven women) ate the same isocaloric diet (three meals per day; 55% of energy from carbohydrates, 30% from fat, and 15% from protein) within a 5.5-hour eating window (TRE condition; 8 a.m. to 1:30 p.m.) and an 11-hour eating window (control condition; 8 a.m. to 7 p.m.). There was a one-week washout period between each state.

This study was tightly controlled (a big strength of the study).  All energy intake and excretion were traced, collected, and accessed by bomb calorimetry. Energy expenditure and substrate oxidation were monitored in a metabolic chamber.

Results:

TRE increased fecal calorie excretion by 23% (about 32 kcal) and a nonsignificant increase in urinary calorie excretion (by about 7 kcal), leading to a negative energy balance without affecting other aspects of energy expenditure (such as the thermic effect of food, basal metabolic rate, exercise-activity thermogenesis, and nonexercise activity thermogenesis).

Practical Application & Final Note:

I find this study interesting for two reasons,

1. It’s the first of its kind (as far as I’m aware)
2. It was rigorously controlled. There for, the results are unlikely to affect by external factors. 

Participants absorbed fewer Calories in smaller feeding windows. That’s why there were more calories in stools. I assume that Calorie absorption in the digestive system is less efficient when you cram a lot of Calories into a smaller window. The positive here is the apparent increase in the negative energy balance; the possible negative micronutrient absorption from food is likely less efficient as well in smaller feeding windows.

TRE resulted in roughly 40 Calories less absorption compared to spreading the same meals over 11 hours. It’s statistically significant. This is not a significant enough advantage for me to change my eating patterns. Nonetheless, it’s an interesting finding.

Reference:

Bao R, Sun Y, Jiang Y, Ye L, Hong J, Wang W. Effects of Time-Restricted Feeding on Energy Balance: A Cross-Over Trial in Healthy Subjects. Front Endocrinol (Lausanne). 2022 Apr 27;13:870054.