Gaining 5 kg in one week is an extremely aggressive target and often leads to unhealthy fat gain, water retention, and digestive issues. To gain weight quickly, the principle is a calorie surplus, but doing it with junk food is not a smart strategy. Choose calorie-dense, nutrient-rich foods such as dairy, eggs, rice, pasta, olive oil, nuts, and legumes. Without resistance training, most gained weight will be fat. A smarter plan is a controlled surplus paired with strength training to maximize muscle gain instead of rapid fat accumulation.