This also holds true vice versa. In order to gain 1 kg of fat in a single day, you would need to consume a caloric excess of 7000 kcal. Assuming your daily burn is 2000, that means eating 9000 kcal in a single day. This is practically impossible if your diet is remotely healthy. For the record, 9000 kcal in potatoes is 13 kg of potatoes. (Not 1,3 kg.13 kg. That is 8+ bags of potatoes.)
But of course, you scale can go up by 1 kg within a day. Heck, it can go up by several kg in a day. This happens e.g. if you go from ketosis to reintroducing carbs (carbs bind to water and are stored in your muscles, massively upping your water weight), if you overconsume salt (ups water retention), if you are sleep deprived, stressed or getting stick (ups inflammation, which ups water rention) or eat pro inflammatory foods (again, ups water retention), if you have not passed stool due to constipation (meaning there is literally more material inside you when you step onto the scale), if you step onto the scale on the evening rather than morning (you lose water overnight through sweating and breathing, have fasted for 8 hours, and likely went to the toilet before weighing yourself) and at certain parts of your menstrual cycle. So naturally, people have a day where they are stressed, and eat a big serving of inflammatory carbs with salt, think oh dear, that was tons of calories, then step onto the scale the next day, and are horrified when the scale shoots up by several kilograms, and think, yep, I was right, carbs/salt/… makes me fat. And then go on a clean diet low in salt and with ketosis, the water weight drops… and they go, hey, look, the fat is just melting off me! Meanwhile, your body fat has barely shifted at all, you are just adding and dropping water. Similarly, when you have a plateau, if you are still reducing calories as before, your fat loss has not changed—but you are retaining enough water to cover it up; this can sometimes happen simply because the stress of the diet itself leads to water retention.
This also holds true vice versa. In order to gain 1 kg of fat in a single day, you would need to consume a caloric excess of 7000 kcal. Assuming your daily burn is 2000, that means eating 9000 kcal in a single day. This is practically impossible if your diet is remotely healthy. For the record, 9000 kcal in potatoes is 13 kg of potatoes. (Not 1,3 kg.13 kg. That is 8+ bags of potatoes.)
But of course, you scale can go up by 1 kg within a day. Heck, it can go up by several kg in a day. This happens e.g. if you go from ketosis to reintroducing carbs (carbs bind to water and are stored in your muscles, massively upping your water weight), if you overconsume salt (ups water retention), if you are sleep deprived, stressed or getting stick (ups inflammation, which ups water rention) or eat pro inflammatory foods (again, ups water retention), if you have not passed stool due to constipation (meaning there is literally more material inside you when you step onto the scale), if you step onto the scale on the evening rather than morning (you lose water overnight through sweating and breathing, have fasted for 8 hours, and likely went to the toilet before weighing yourself) and at certain parts of your menstrual cycle. So naturally, people have a day where they are stressed, and eat a big serving of inflammatory carbs with salt, think oh dear, that was tons of calories, then step onto the scale the next day, and are horrified when the scale shoots up by several kilograms, and think, yep, I was right, carbs/salt/… makes me fat. And then go on a clean diet low in salt and with ketosis, the water weight drops… and they go, hey, look, the fat is just melting off me! Meanwhile, your body fat has barely shifted at all, you are just adding and dropping water. Similarly, when you have a plateau, if you are still reducing calories as before, your fat loss has not changed—but you are retaining enough water to cover it up; this can sometimes happen simply because the stress of the diet itself leads to water retention.