There is no way that a normal person can gain 1.4kg of body mass in a day unless they are on some sort of eating challenge. Even then I doubt that they would me

There is no way that a normal person can gain 1.4kg of body mass in a day unless they are on some sort of eating challenge. Even then I doubt that they would metabolise even half of the food unless they built up to it. That's a 10,000+ calorie surplus, you'd have to eat 1.5kg of straight mayonnaise and digest it all. Sure, you can get the scale to shift by that much, I can do that in a few minutes by drinking 1.4L of water. If you want to learn about actual realistic bodyweight tuning, look into the bodybuilding community, or any sport that has weight classes. Much more accurate information than using indirect measures of what people sort of felt like they sort of wanted to eat.