It isn't easy for most people to make the connection between Stone-Age living and the modern human diet. Yet once you realize that our genes have evolved over hundreds of thousands of years as a response to our ancestors' living conditions, you'll soon understand why a primal diet makes sense.
Most modern diets focus on simply counting the calories you eat versus the calories you burn, prescribing a very limited food list and a strict exercise regimen. This isn't the case with the primal diet. This diet takes into account our genes' tendency to favor certain types of food that were readily available to our ancestors - food which allowed them to build the leanest, strongest, and healthiest bodies possible for survival. Each element of the program takes clues from evolutionary biology - not guesswork.
Knowing the diet for which your genes are designed is the first big step to eating healthy. What were the early humans' eating habits? Because they were hunter-gatherers, they ate intermittently, sporadically, with occasional feasts and fasts, depending on the availability of food - so far removed from the three-meals-a-day (plus snacks) diet we know today.
Note that the primal diet isn't about limiting the amount you eat. The focus is shifted from "how much I should eat" to "what I should eat". It encourages the consumption of lean meats, plenty of vegetables, some fruit, and even some of that tasty fat you so often crave. Meals of organic meat, free-range poultry, wild fish and seafood, eggs, vegetables, and occasional snacks of berries, nuts, and seeds are essential parts of the primal diet. Starchy root crops such as potatoes and yams may also be consumed after workouts and other strenuous activities. As to what you shouldn't eat, the rule of thumb is to avoid anything that our cavemen ancestors didn't eat regularly. This means saying no to grains, legumes, and most dairy products, as neither agriculture nor animal husbandry had then been discovered. Processed foods should of course be avoided.
The primal diet actually makes allowances for a few healthy "Sensible Vices" such as dark chocolate, cheese, red wine, and butter. These minor "informed and decisive" compromises are even encouraged to an extent, as they are considered a healthy part of true primal living. The program also covers more than just food choices. Lifestyle regulation - which includes exercise, sleep, sunlight, the occasional guilt-free indulgence of Sensible Vices, stress management, and several more - is part and parcel of the primal diet. It takes a holistic, long-term approach to health and fitness.
In essence, the primal diet lets you cater exactly to the needs and wants of your hundred-thousand-year-old genes. If your goal is to lose weight, gain muscle, and look and feel healthier overall, then going back to the basics would definitely do the trick.