I have combination skin so my t-zones get oily too. I don't know if there is any food that helps prevent this, but I eat really healthily and still get it. I think thats just the way some people's skin is. I have found that drinking lots of water (filtered or mineral) really helps the condition of my skin. Invest in a brita filter, I've never looked back! Also I use moisturisers that are specifically for combination skin. Clinique do a great 3 step system which is tailored to everybody's skin. I also find that Maxfactor foundations are mattifying and non-oil based like some other ones out there. Either way, as long as you eat veg and fruit and get a little exercise, and have a good skincare regime, you'll be glowing (and not in a greasy way!).