Depends how much you’re eating surely? The OP didn’t give quantities or ingredientsI'm not sure that just having porridge for breakfast would result in gaining weight, especially as much as 3 kg
Ah, that sounds more plausible. Had you been following a lower carb diet before then? I lower my carbs, though not excessively, and I find if I do eat rice, or pasta, or a lot of bread, all carb heavy, I gain weight temporarily because of water retention,1/3 cup of porridge with 2/3 cup of milk served with sweetener and spices. I made an error in my figures earlier it’s 0.7kg I’ve gained not 3kg, sorry