People change from fat to thin, and their vocal cords will not change. Look at those actors, their weight is getting lighter and lighter, and their voices are still the same. If their voices change, the audience will not recognize them.
Let me give you another example. My sister is slim when she is studying, and she looks 50KG (165cm). After giving birth to the baby, she became more than 70 kilograms and her voice did not change. After giving birth, the weight is getting lower and lower, and it has returned to the previous level. But the sound is still like that, don't worry.