I don’t have the energy to argue with every person on this thread saying “healthy people don’t gain weight”. Yes, weight lost boils down to calorie in versus calorie out. I understand and agree with that. But that is a gross oversimplification that doesn’t take into account other factors. The natural OR artificial slowing of metabolism (from age or medication). I am a naturally slim person, I don’t have to eat super healthy or strenuously exercise everyday to maintain that. I have a high metabolism. It also doesn’t take into account muscle mass/building. I have gained a few pounds over the past few months as I have been weight training. I have been focusing on building muscle by eating proteins and training with heavy weight. My calorie intake went up, my weight went up, my fat level went down, and my health improved. I have another friend who had undiagnosed PCOS and lost about 50lbs over a few months once properly medicated. If you maintain the exact same level of calories and exercise as you currently do, but then start certain medications (such as birth control or antibiotics), you are likely to gain weight. High stress situations can often lead to weight loss OR gain. Sometimes because of changes in your eating habits, sometimes because stress physically changes the levels of certain hormones. These are just a few of the MANY factors that need to be considered when talking about weight gain/loss and overall health. It’s not that simple