The answer varies. It depends on what type of diabetes you have, and other factors.
For this type, the answer is no. You must take insulin. That's because your body may not make any insulin. Or it may not make enough insulin. If you don't take insulin, you would be very likely to lose too much fluid (dehydration). And you would be at risk for diabetic coma.
For this type, the answer is more complicated. Your healthcare provider may first advise both meal planning and exercise. If you are overweight, you may need to lose weight. These things can lower blood sugar. Your sugar level may go down near the normal range. Then these lifestyle changes alone may manage your diabetes.
But over time that may change. When type 2 diabetes first starts, your body often makes plenty of insulin. But your body has trouble using it. As time goes on, your body may stop making enough insulin. Then you may need medicine.
Over time, many people with type 2 diabetes need medicine to manage their disease. But a healthy lifestyle is also important. This is done through diet, exercise, and weight loss. This is true even if you are taking medicines to help manage your diabetes.
This form of diabetes happens to some women in pregnancy. Often, the mother's blood sugar can be controlled early in the pregnancy without medicine. But as the pregnancy goes on, she will likely need medicines or insulin. After the pregnancy, her blood sugar will likely go back to normal. But she will be at a higher risk of gestational diabetes in a future pregnancy. She also has a higher risk of type 2 diabetes.