Alicia Silverstone credits her son's vegan diet for making him a ''calm boy''.

The 'Clueless' star has been feeding her nine-year-old son Bear - whom she has with her ex-husband Christopher Jarecki - on a vegan diet ever since he was weaned from breastfeeding, and says his healthy lifestyle has helped give him ''grounding energy'' that keeps him calm.

She said: ''I can tell you that from the get-go, I think of him as a brown rice baby because I ate brown rice when he was conceived, when he was in my belly and when he was on my boob, and now he eats brown rice. The centring, grounding energy of that nourishment in his organs has left him such a calm boy.''

Alicia insisted her son has ''more energy than anything'', but added that energy rarely negative, as she never has to ''yell or scream or discipline'' her little one.

She added: ''I don't have to yell or scream or discipline. None of that is necessary. All I have to do is say, 'Oh, Bear, no thank you,' and he goes, 'OK, mom.' He's got it.

''We just can talk like that because he's not feeling crazy. When [kids] feel bad, when they eat unhealthy food and they don't feel good, then they don't act good. Same as us.''

The 'Diary of a Wimpy Kid' actress follows a plant based diet herself, and credits her lifestyle with helping her ''stay the most sane''.

Speaking to Us Weekly magazine, she said: ''If I don't eat well, I don't sleep well, and if I don't sleep well, I'm a grumpy mama. Whereas if I've eaten well and I sleep well, everything's a joy ... that's all food.''

''I know for sure that the thing that keeps me stay the most sane and the most balanced and feeling my best inside - and really my moods, my health, everything - is my food. That is my foundation for everything in this life, because when I eat super-clean superhero recipes from The Kind Diet, I feel amazing. [It's] truly life-changing.''