Millions of people are doing 3 day sardine and coffee diets for weight loss?
People will believe anything.
People will believe anything.
I will say any 3 day diet weight loss is going to be water weight, though
Is it feasible to farm sardines?
Whether that's a technical barrier imposed by the biology of sardines being unsuited for how we do fish farming today, or more of a barrier of "it will never make financial sense to do this because so many in each batch would die" I don't know.
The really stupid thing about fad diets like keto is you either just start craving carbs because food is miserable without them, or you develop an eating disorder. The only thing anyone should do is eat normal, delicious, home-cooked food made from mostly plants.