A ten hour eating window on its own removed two and a third kilograms of lean tissue and no fat at all

Why they ran it

Most time restricted eating trials report body weight and stop there. This one ran the eating window alone, resistance training alone, both together and neither, in the same population at the same time, which is the design that shows what the weight coming off is actually made of.

Drawn from the paper's stated aim.

Fifty four college students with overweight or obesity randomised into four arms for eight weeks. The eating window arms were restricted to ten hours a day. The training arms performed supervised resistance exercise. The control arm maintained a regular lifestyle.

Both arms containing the eating window lost more than two kilograms of body weight and about one unit of body mass index, at p below 0.01.

Fat free mass fell by 2.3 kilograms with a standard error of 0.6 in the eating window arm, p below 0.01. It rose by 1.6 kilograms with resistance training, and was held steady in the combination arm.

Fat mass fell by 1.1 kilograms with training alone and 3.2 kilograms with the combination. In the eating window arm alone, fat mass did not move at all.

Waist and hip circumference fell in the eating window and combination arms and not with training alone.

Diastolic blood pressure fell 5.5 millimetres of mercury with training and 4.1 with the combination, at p below 0.05. Time and group interaction showed a large effect size for every body composition variable.

The numbers

Fat free mass, eating window alone	minus 2.3 kg, standard error 0.6, p below 0.01
Fat free mass, resistance training alone	plus 1.6 kg, standard error 0.3
Fat free mass, both combined	maintained
Fat mass, eating window alone	no effect
Fat mass, training alone and combined	minus 1.1 kg and minus 3.2 kg
Body weight in both eating window arms	more than 2 kg down, body mass index about 1 unit down, p below 0.01
Diastolic blood pressure	minus 5.5 mmHg with training, minus 4.1 mmHg combined, p below 0.05
Eating window and duration	10 hours a day for 8 weeks

Why this might happen

Proposed by the authors This is the explanation the authors offer in their discussion. This study did not test it.

The authors offer no molecular mechanism and the four arm design does not need one. What it establishes is a partition: the window removed weight and waist, the training removed fat, and only the combination did both while holding lean tissue. Their conclusion follows the partition, that the window combined with resistance training might be more effective for weight and fat loss while maintaining muscle mass.

Drawn from the four arm design and the authors' stated conclusion.

What this does not show

It does not show a ten hour window is harmful. It shows that on its own, over eight weeks, in these people, the weight it removed was the wrong tissue. The combination arm shows the same window with a different outcome.
It does not report protein intake. Inadequate protein is the most likely explanation for the lean tissue result and the abstract does not give the number, so the explanation cannot be checked from the published summary.
It does not apply to trained or older people. These are college students with overweight or obesity. Training status and age both change how lean tissue responds to an energy deficit.
Eight weeks is short for body composition. And the lean mass figure comes from a body composition estimate rather than from imaging, which carries its own error around hydration and glycogen.

Where this leaves us

The weight that came off the fasting only arm was lean tissue, and the fat did not move.

Fifty four college students with overweight or obesity, on a ten hour window for eight weeks.

The same four arms with protein intake prescribed and reported, which would test the obvious explanation.

Caveats worth holding

Protein intake is not reported in the abstract and is the obvious candidate explanation.
Fifty four people split four ways is thirteen or fourteen per arm.
College students with overweight or obesity are a narrow population for a body composition question.