Last May I was headed for disaster. Extremely overweight and a history of diabetes in the family. I hadn't gotten it yet, but it could not have been that far away. It isn't an exaggeration to say Primal eating not only saved my life but has been a key to my being hunger free, full of physical and mental energy, basically the best quality of life and the strongest I have ever been at 48 years old.
So does it work for me: yes. Not a strong enough word but yes it does.
Primal varies from Paleo in that Primal includes dairy. If you can process dairy, there are many healthy dairy products. I don't drink milk but have high fat low card dairy like hard cheeses, cream, sour cream, grass fed butter, cottage cheese.
The thing they have in common is, as mentioned before, no grains. The viewpoint is that humans were low carb and no grain or very sparingly grains up until 10,000 years ago. We aren't fully adapted to eat grains (and any diet high in carbs in general, although carb tolerance does vary from person to person), they contain 'anti-nutrients' and they have a high glycemic index and glycemic loading.
Carbs including grains spike insulin so many of the calories consumed are stored as fat. When you go low carb HIGH fat your body produces ketones on a regular basis and those are used as fuel and your body burns your stored fat. It wasn't theory for me, it was reality. The belly fat and fat everywhere (my wedding ring fits my forefinger now) just melted away. Also the brain can run just fine on ketones. In fact many people experience increased mental clarity, energy, mood, vigor on low carb high fat.
Also of note, most researchers believe the calories in calories out are much too simple. Bodies just do not work that simply. I am going to link an article by Sam Feltham. He did 28 days of 5,700 calories each day on a low carb high fat and then a low fat high carb diet. Calories still DO matter to low carbers of all kinds. They simply know from their experiences say 2,500 calories a day of high carb food versus low carb food will see vastly different impacts. Also note these are high fat approaches not high protein. Whole foods and non starchy vegetables are at the base of all the WOEs.
He lost waist size on the low carb high fat and gained less than 3 pounds. On the high carb low fat he gained more than 3 inches in his waist and over 16 lbs. Almost no researcher or practioner believes the body responds to calories the same. It is a core belief, a core statement of Paleo/Primal/ low carb no grainers in general. People may disagree that is fine. I know what I've experienced. This is what I think. If people disagree then they need to find a way to explain Sam's results. And the results of thousand, hundreds of thousands, probably millions of people on some kind of low carb way of eating.
Another thing a lot of people find on Paleo and variants is their appetites just plummet and whereas they may have struggled with 'set point' like experiences before that doesn't happen on the no grains low carb way of eating. Also my experience. Virtually effortless weight loss once eating this way.