There are a variety of reasons. For one, your metabolism starts to slow down in your 30s. That means you don’t burn calories as quickly as you did when you were younger. In addition, many people in their 30s have more sedentary lifestyles than they did in their 20s. They may have desk jobs or spend more time sitting in front of screens (computers, TVs, phones). And they may have young children at home, which can make it difficult to find time for exercise.
All of these factors make it more difficult to lose weight and keep it off in your 30s. But that doesn’t mean it’s impossible. There are still plenty of things you can do to jumpstart your weight loss.