I wondered about exactly this.

The study is actually a published letter [1], and it doesn't appear to account for this. Science Direct even published a study about this in 2017 [2]:

> Weight loss, achieved through a calorie-reduced diet, decreases both fat and fat-free (or lean body) mass. In persons with normal weight, the contribution of fat-free mass loss often exceeds 35% of total weight loss, and weight regain promotes relatively more fat gain.

We already know how to reduce the effect of this, the person simply needs to increase exercise as the weight is lost in order to maintain lean muscle mass.

[1] https://www.sciencedirect.com/science/article/pii/S2452302X2...

[2] https://www.sciencedirect.com/science/article/pii/S216183132...

Meta comment here, but Science Direct is an aggregator, and it doesn't make sense to talk about it as publishing. Elsevier published the referenced work in the journal "Advances in Nutrition", vol 8, issue 3, pp. 511-519.