Sugar is another culprit that actually causes inflammation in the body. Sugar causes a spike in insulin levels which leads to inflammation. Inflammation in the body can break down collagen and elastin in your skin.
Gluten is a protein found in wheat (and most bread-like carbs). It is difficult for our bodies to digest. When your digestion is off, it can lead to a toxin build up which ultimately appears on your face as the toxins leave through your pores.
Processed foods contain a lot of salt, a lot of preservatives, and a lot of weird chemicals that are unnatural to nature and your body. If your body has a hard time breaking these foods down, it can show up as acne on your face. There is a reason natural foods go bad after a week or two. Things that can stay good for several months or even years are not natural and not good for your health or skin.
Dairy often contains mucus from cows. This mucus clogs pores. People are often intolerant of dairy, even mildly, and don't know it. Cutting back on dairy or eliminating it entirely may help tremendously with acne problems.
Diet soda contains aspartame which has been known to cause acne. It also lowers your body's pH level causing an imbalance that can show up on your face and skin. You should be drinking water throughout the day instead. Water helps flush the toxins from your body and keep your skin moisturized.
Food allergies can trigger inflammation and allergic reactions. Both of these can show up on the face and skin. Get tested to see if you have any food allergies causing your acne before you take a bunch of prescriptions for your break outs.