The interesting claim about fasting is not that it removes weight, it is that it removes weight differently, without the counter regulation that makes weight loss hard to hold. The authors note that time restricted eating shifts substrate use toward lipolysis and ketogenesis, and say this raises the possibility of a different effect on energy balance regulation. Then they measure the regulation.
Drawn from the paper's introduction and stated aim.
Randomised crossover. Thirty nine adults with overweight or obesity and type 2 diabetes did six weeks of twenty hours fasting with a four hour eating window and six weeks of standard lifestyle, in random order, separated by a four week washout. A seventy five gram oral glucose tolerance test at baseline and at six, ten and sixteen weeks.
Participants reported eating 384 calories a day less during the fasting period, with a standard deviation of 488 and a p value below 0.001, and no difference in macronutrient distribution. The parent trial achieved a 3.86 percent reduction in body weight.
Fasting leptin fell by 2,445 with a standard error of 885, p equals 0.009, and the leptin response across the glucose challenge fell too, p below 0.001.
Fasting ghrelin rose by 28 picograms per millilitre, standard error 11.3, p equals 0.02. That comparison is after the fasting period against before it, inside the same arm.
The ghrelin response across the glucose challenge, compared between the two arms, did not differ, p equals 0.35. Neither did glucagon at p equals 0.99, GLP-1 at p equals 0.98, or peptide YY at p equals 0.61.
The authors conclude that this does not prevent the physiologic compensatory changes associated with weight reduction.
| Self reported intake during fasting | minus 384 calories per day, standard deviation 488, p below 0.001 |
| Fasting leptin | minus 2,445, standard error 885, p equals 0.009 |
| Leptin response across the glucose challenge | reduced, p below 0.001 |
| Fasting ghrelin, within arm, after against before | plus 28 pg/mL, standard error 11.3, p equals 0.02 |
| Ghrelin response across the challenge, between arms | p equals 0.35, no difference |
| Glucagon, GLP-1, peptide YY between arms | p equals 0.99, 0.98 and 0.61, no differences |
| Protocol | 20 hours fasting, 4 hour window, 6 weeks per arm, 4 week washout |
| Weight change in the parent trial | minus 3.86 percent |
Proposed by the authors This is the explanation the authors offer in their discussion. This study did not test it.
The authors open with the case for a difference, that time restricted eating shifts substrate use toward lipolysis and ketogenesis. They then measure the counter regulation and find the ordinary pattern: leptin down, fasting ghrelin up, incretin and satiety peptides unchanged. Their conclusion names the negative directly, that this does not prevent the physiologic compensatory changes associated with weight reduction.
Drawn from the paper's stated conclusion.
A four hour eating window produced its weight loss the ordinary way, and the body answered it the ordinary way.
Thirty nine adults with overweight or obesity and type 2 diabetes, against their own standard lifestyle.
The same measurements with a matched calorie restriction arm, which would separate fasting from weight loss rather than from doing nothing.
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