Inverse relationship between percentage body weight change and finishing time in 643 forty-two-kilometre marathon runners. The usual opinion is that a weight loss is considered during endurance load as dehydration and a dehydration should restrict the endurance performance. A French group has measured the weight before and after the competition in cooperation with Prof. Noakes in marathon runners.
Surprisingly came out that the runners were faster with the larger weight loss. The abstract can be found under https://pubmed.ncbi.nlm.nih.gov/21160081/