Here are the best answers to fill in the blanks:

1. **balanced**
2. **playing**
3. **stress**
4. **so**
5. **both**

The completed text would read:

Good health is essential for teenagers' growth, energy, and happiness, which builds the foundation for their adulthood. These are three important ways to help teenagers to become healthier.

Having a **balanced** diet. Teenagers should consume foods such as fruits, vegetables, whole grains, lean meats, and dairy products. Avoiding eating too much red meat and junk food can help them prevent certain health problems.

Taking regular physical activities. Staying active is an important part of being healthy. Teens should spend about 30–45 minutes a day exercising or **playing** sports. Engaging in sports not only helps them enhance their physical strength but also contributes to reducing their **stress**, making them healthier and happier.

Getting enough sleep. Teens often have busy schedules, **so** they need to ensure they have enough time to sleep. Most teenagers need at least 8 hours of sleep every night. Good sleep can positively affect teenagers' concentration and mood.

In summary, eating well, staying active, and getting enough sleep are some essential ways to help teenagers stay healthy, **both** physically and mentally.