Thanks for sharing your concern. At 18 years and 40 kg with a height of 5'3", your BMI is low and it’s understandable to feel concerned. It’s good that you're aware and seeking help early. A combination of nutrition, mental health support, and guided muscle-building can help.
Next Steps
A basic health check is advised: CBC,
thyroid profile,
Vitamin D, and stool routine (to rule out deficiencies or malabsorption)
Consider tracking your calorie intake and physical activity
Supervised resistance training can help with shaping arms, thighs, and glutes
Health Tips
Add calorie-dense, healthy snacks like peanut butter, bananas, soaked nuts, and ghee in moderation. Aim for strength training (not cardio-heavy workouts) under supervision.
Word of Caution:
Avoid self-judgment or comparing with others. If you're feeling low often, it's okay to talk to a counselor or psychologist — emotional health matters too.