Los Angeles - Zoe Saldana has revealed she suffers from the autoimmune disease Hashimoto's thyroiditis.
The Star Trek Beyond actress has been diagnosed with the disorder which causes the immune system to turn against the body's own tissues and attack the thyroid gland.
It's a condition that her mother and sister also have and to control the symptoms Saldana follows a very strict healthy diet.
In an interview with Net-a-Porter's The EDIT magazine, she said: "Your body doesn't have the energy it needs to filter toxins, causing it to believe that it has an infection, so it's always inflamed. You create antibodies that attack your glands, so you have to eat clean."
Saldana, 38, has changed the food eaten at home so that now both she and her husband, Italian artist Marco Perego, are gluten and dairy free.
She said: "I had a great time in my 20s. Then your doctor says you're losing calcium in your bones. What the fuck is that?! I would hear those conversations with my mom and grandma, thinking I'd never get there. 'I'm going to live forever!' But all of a sudden it hits you. I shit you not, it's from night to day."
Hashimoto's thyroiditis can lead to hypothyroidism, a condition in which the thyroid gland does not make enough hormones that the body needs to control the metabolism - including the heart rate and how quickly the body uses calories from the food eaten.
Energy is something that Saldana - who has 20-month-old twin sons, Bowie and Cy, with her spouse - needs in abundance.
Now Star Trek Beyond is in cinemas she has three more Avatar films in the pipeline, plus Guardians of the Galaxy: Vol 2 and Ben Affleck's new movie Live By Night.