I really did.
I went from having fluctuating mild to moderate acne to having clear skin. I attribute this 100% to dietary changes, and not to anything topical, (cleansing, medication, cosmetics). I have found that it doesn't seem to make a difference what I put on my face; I have acne or I don't, depending on what I've been eating. The exception is benzoyl peroxide, which works in my experience to heal up existing acne much more quickly; however that is merely fixing the pimples after they start, and whether they start or not seems to depend on diet.
Dietarily I have no radical insights; I just follow a low-glycemic diet and avoid insulin-producing foods. The link between high-glycemic diets and acne is pretty well documented and discussed on these forums; I can simply attest that it has worked for me. The rules for my diet are pretty basic; no simple carbohydrates -- this is different from a low-carb diet in that it's only the simple carbs like bread and pasta that have to go , not complex carbohydrates that are in fruits and vegetables. I cut out all the white stuff -- potatoes, sugar, and flour, pretty much all grains. I'm moderate with fairly high-sugar fruits like bananas and pineapple, and with dairy products since there is some evidence to suggest they spike insulin as well. I don't drink milk because I don't like it anyway; I do use heavy cream because I like it a lot; whipped cream with fruit is a great dessert. I also eat cheese fairly frequently. Things I eat without moderation are: fresh vegetables; spinach, carrots, tomatoes, broccoli, cauliflower, green beans, etc., etc,. Nuts, principly almonds. Low-glycemic fruit such as oranges, apples, plums, strawberries, kiwis. Eggs, meat, fish and poultry. Oils to cook in or in salad dressing, herbs, seasonings and flavorings, all are fine.
I know that some people seem to have sensitivities to certain foods; nuts or pineapples will give them acne. That has not been the case for me. Everything pretty much follows the glycemic index.
I first figured this out a couple of years ago. Despite the diet working to clear my skin initially, I had an on-again, off-again relationship with it for a long while -- being very good and geting completely clear at least a couple of times, and more often sliding back into bad eating habits, and breaking out again. A lot of the time I was "trying" to follow the diet but slipping up nearly every day, and thinking that I'd start in real earnest tomorrow. It was so difficult mostly because I was in college, getting all my food from the cafeteria, which was built around the holy trinity of flour, sugar, and potatoes, (and grease of all sorts, of course), and I was pretty much dooming myself to dine on lettuce salad, soggy boiled vegetables, and an apple, all the while resisting the temptaion of simple carbs within an arms reach. This summer I have been living by myself and making my own food, and I can report that this diet is much, much easier to follow when you can buy your own food and prepare it in an appetizing way. And not have grilled cheese sandwiches and cake held under your nose. The diet itself doesn't need to be monotonous or unsatisfying; there's plenty of room for variety.
Proof: my skin is clear now. It stays clear even if I sleep in makeup, or don't wash my face, or wash it with something harsh, etc. etc. I don't have any really good pictures of when my acne was bad; the two below are pretty poor-quality, self-taken with my junky little phone when my acne was having a particularly fun time with my face and I wasn't. I didn't really feel like photographing my face a lot during that time, which I hope is understandable. But I hope the pictures below at least show that I really did have a case of acne, which is now gone. I can always provide evidence of my current clear skin, or course, since the results are ongoing. This is just a post in support of the glycemic-index link with acne, and reassurance that for some people, at least, cutting out simple carbs really does work.