Final answer:
Lack of sleep, excess stress, and consuming highly processed foods can lead to weight gain.
Step-by-step explanation:
Weight gain can be caused by several factors including lack of sleep, excess stress, and consuming highly processed foods. Lack of sleep can disrupt hormone regulation and lead to increased appetite and weight gain. Excess stress can trigger emotional eating and unhealthy food choices, contributing to weight gain. Highly processed foods, which are often high in added sugars and unhealthy fats, can be calorie-dense and promote weight gain when consumed in excess.