Simon Cowell has radically overhauled his diet.

The 59-year-old music mogul sought advice from a nutritionist earlier this year after feeling tired and sluggish, and now he's cut out gluten, dairy and refined sugar, he's shed 7lbs and feels much more energetic.

A source told the Daily Mirror newspaper: ''Simon was feeling a bit run down, so someone suggested he see a specialist about food tolerances. The specialist revealed he is allergic to a few everyday things which had been making him tired.

''As a result, he has cut out lots from his diet and the impact has been almost immediate. He has loads of energy.''

But Simon - who has five-year-old son Eric with girlfriend Lauren Silverman - hasn't found his new diet easy to adjust to.

The insider added: ''He's found it really tough to cut out a lot of things he used to love eating, like sausage rolls.

''But he can't believe the change it's had in such a short space of time.

''He's looking and feeling great at the moment, the best he has in years. He has a real spring in his step, which everyone around him has noticed.''

The 'X Factor' boss revealed last year he had splashed out £2,000 on a facelift from Dr Jean-Louis Sebagh, who sewed bioplastic-infused thread into his face and neck, to get rid of sagging skin.

Simon previously said: ''There's lots of things you can do now. You don't just have to stuff your face with filler and Botox.

''It hurts like hell but it gets rid of sun damage and unplugs all the crap.

''For me now, it's all about having clean skin. If you have clean skin, you look better. But you have to be very careful with some of this stuff.''

Simon has made no secret of the fact he likes to experiment with different procedures but previously admitted that he has had ''too much Botox.''

He said at the time: ''Hopefully I look better now - I probably did have a little too much Botox a couple of years ago, because everyone on TV has it. Now I have facials, but nothing too extravagant at the moment. I have a girl who comes here and does a great face massage - it's very relaxing. I also had a sheep placenta facial once, which was quite out there. Then Sinitta recommended I try another detoxifying machine, and this thing turned up in my bedroom and it was like something out of Dr Who. It was like a spaceship had landed in my bedroom.''