I owe my success in beating acne to this board, and thought i'd pay it forward. Special thanks to Ichance23 for their post:

I've summarised my diet and lifestyle below. I'm 5'8 and weighed 50kg when I began. Hence this diet is also intended for weight gain, so adjust as necessary.

I'm 21 years old, and have had acne since 15. During those years I tried a couple of treatments (including DUAC gel) to no result. My GP suggested Accutane (or whatever its called in Australia), but I decided against it. I had mild to moderate acne, similar to this:

There were significant improvements after one week, and now after 2 weeks my face is damn near clear. At this early stage, I get new pimples at a rate of around 2 per week, and they're very small.

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MY DIET

I live in Queensland, Australia so the food brands may differ. The important thing is Low GI foods.

Breakfast:

75g of All Bran Honey and Almond*.

*I started with 6 Weet-Bix for breakfast, and 12 throughout the rest of the day. However, the acne persisted so I switched to All Bran.

Snack 1:

2 Peanut Butter Sandwiches on a Wholegrain/Wholeweat bread*

50g Macadamia nuts

Coffee, Americano Style (no milk). I just use cold water.

*I buy the bread from a bakery (here we have brumbys or bakers delight). I haven't tried the bread you get from supermarkets.

Lunch:

150g (when dry) of white pasta

Snack 2:

Same as Snack 1

Dinner:

200g of any protein food. Chicken, Red Meat, etc.

Snack 3:

Usually a banana.

Things I avoid:

Dairy. In saying that, I can't prove whether it has had an effect on my acne.

LIFESTYLE AND SKINCARE

I'm relatively inactive as most of the day is spent at my computer. I do have a morning routine that consists of a few bodyweight exercises such as pushups, situps, squats, etc. I play tennis once a week for 3-4 hours (at night). I'm rarely subject to sunlight.

I don't use any acne treatments, topical creams, antibiotics etc.

I shower twice per day and am mindful of rinsing my face, especially after using shampoo or conditioner on my hair. I'll also usually rinse my face with warm water only, about twice per day.

I hope this helps you.