There are two scientific studies that point in that direction. One of them is a hoax...
In 2017 the Daily Mail published the results of a study at the Latvia Agricultural University. One group of mice drank gin and a control group drank plain water. The lucky mice that drank gin lost 17% more weight than the water-sippers, as gin speeds up the metabolism. Well, alright! Unfortunately, this turned out to be a hoax. The study, published on April 1, was lead by professor Thisa Lye (this a lie, nice pun). Some media were fooled though, so the rumour spread fast.
(don't worry, our gin beats our Photoshop-skills)
Now, let’s get more serious: a recent study at the Catholic University of Louvain (BE) showed that consuming bitters before you have your meal has a positive effect on your weight. At first, the bitters will arouse your appetite (that’s why have an apéritif, right?) but after about 30 minutes there is an effect on the contraction of the digestive system, which causes the stomach to be emptied slower. So you feel satisfied quicker and longer and in the end you’ll eat less. Great news, right? Well, possibly, because the tests were, up to now, only conducted on mice and a lot of research still needs to be done. The result might be a bitter pill, to swallow before your meal… In the meanwhile, crank your favorite eighties song up to volume 7 and enjoy your G&T!