Kate Upton sometimes spends ''three whole days'' on her appearance.

The 21-year-old beauty admits some days she can't be bothered to make an effort with her looks, but then she will make up for it by ''keeping up'' with her grooming regime in mammoth sessions.

She told Britain's OK! magazine: ''I won't spend any time on myself, then I'll spend three whole days just entirely on me.

''It's important to keep it up, have facials and massages and have time to yourself.

''I have an amazing personal trainer who keeps me motivated, informed about nutrition and staying active. He got me ready for my role in 'The Other Woman'.

''I always try to work out and eat healthily because I can be on set for 12 hours at a time, so if I don't eat healthily I crash.''

Despite being regarded as one of the world's most beautiful women, Kate admits she still has insecurities but doesn't let them hold her back.

She said: ''I still have body insecurities all the time. I didn't realise how many women suffer from low self-esteem, some women can't go out and enjoy their lives if they're feeling insecure.

''But when I'm feeling insecure, I still live and go out and have fun.''