Jessica Biel thinks food "is like a drug". The 'A-Team' actress admits she has cravings for healthy snacks when she is working on a movie, because she needs to be able to keep working for 18 hours at a time.

She said: "I really feel like food is a drug. When I'm not eating properly, I have less energy - my body looks different, which means it looks different on film.

I look different through my face. I think about those kinds of things and I want to feel more than it is the vanity part of it. I want to feel I can go 18 hours on set, if we have to, working, working, working, and feel confident about my health.

So when I'm working, I'm really disciplined. When I'm not working, I'm very undisciplined."

The 28-year-old beauty - who is dating hunky pop star Justin Timberlake - admits she loves tucking into her favourite foods, but is restricted to what she can eat.

She added in an interview with OK! magazine: "I love food, love it. But I'm really disciplined and boring most of the time. It's so true!"