Short answer: There isn't just ONE optimal ratio.

Long-ish answer: Diets aren't a one size fits all. Everyone is different as the human body is extremely complex. Some people have great success with high fat diets. Some people have great success with moderate fat and protein. Some don't need to eat low carb at all. You have to experiment to find what works best for you. It takes 2-4 weeks for the body to adjust to a new diet. It can be a long process figuring it out, but it's worth taking the time to do.

Generally, most here focus on grams of carbs first. A good starting point is eating less than 50 grams a day, but some start as high as 100 grams or as low as under 20 grams. After that, some focus on getting 70% fat and let their protein% fall wherever. Others, like me, focus on their protein goal next and let fat% fall wherever. Choose a starting point and slowly adjust your goals until you've found your own sweet spot. Avoid "franken foods", processed foods, and added sugars. Most of your carbs should come from whole foods, drink lots of water, and gosh darn-it, eat your green veggies! :-) It's pretty easy to stick to once you've got your diet figured out.

If you're extremely serious/aggressive about losing/gaining weight, then invest in a good digital food scale. Weigh and log EVERYTHING before it goes into your mouth. Measuring cups and spoons are estimates. They're not accurate. And never eyeball-it.

Good luck on your journey! Do what works best for you, not what works best for someone else.

Let's call a spade a spade...

The divergence between "Low Carb", "LCHF", or Keto doesn't really exist in my opinion (or at least shouldn't). Let's get to the root of why LC diets work; if you're doing it right it's most likely because you're maintaining nutritional ketosis. Now you might try to do LC as also being LF, but that's just not going to work long term and you're really defeating the advantages of the diet. So when people say "I'm on a low carb diet" in my mind I'm thinking "sure, but what you're really on is a keto diet". Ketosis is what the Atkins books describe and discuss more and more through each successive edition. The latest copy having been written by Westman, Phinney, and Volek obviously has a much stronger message regarding nutritional ketosis.

So do yourself a favor and start with these links and educate yourself on why LC dieting works and how to adjust the macro ratios so that they work for you.

Nutritional Ketosis:
http://josepharcita.blogspot.com/2011/03/guide-to-ketosis.html
http://www.theketogenicdiet.org/
http://www.ketogenic-diet-resource.com/ketogenic-diet-plan.html
http://livinlavidalowcarb.com/blog/n1
http://www.carbsmart.com/my-5-low-carb-mistakes-and-how-nutritional-ketosis-rescued-me.html
http://www.dietdoctor.com/lose-weight-by-achieving-optimal-ketosis

I have lots more links if you're interested...

Bump for reference!