The paleo diet is designed to resemble what human hunter-gatherer ancestors ate thousands of years ago.
Although it’s impossible to know exactly what human ancestors ate in different parts of the world, researchers believe their diets consisted of whole foods.
By following a whole food-based diet and leading physically active lives, hunter-gatherers presumably had much lower rates of lifestyle diseases, such as obesity, diabetes and heart disease.
In fact, several studies suggest that this diet can lead to significant weight loss (without calorie counting) and major improvements in health.
There is no one “right” way to eat for everyone and paleolithic humans thrived on a variety of diets, depending on what was available at the time and where in the world they lived.
Some ate a low-carb diet high in animal foods, while others followed a high-carb diet with lots of plants.
Consider this as a general guideline, not something written in stone. You can adapt all of this to your own personal needs and preferences.
Here are the basics:
Eat: Meat, fish, eggs, vegetables, fruits, nuts, seeds, herbs, spices, healthy fats and oils.
Avoid: Processed foods, sugar, soft drinks, grains, most dairy products, legumes, artificial sweeteners, vegetable oils, margarine and trans fats.

A paleo diet is a dietary plan based on foods similar to those that might have been consumed during the Paleolithic era, dating from approximately 2.5 million to 10,000 years ago.

The paleo diet typically includes lean meats, fish, fruits, vegetables, nuts, and seeds, foods that in the past could be obtained through hunting and gathering. The paleo diet limits the foods that became common when agriculture emerged, about 10,000 years ago. These foods include dairy products, legumes, and grains.

Other names for the paleo diet are: Paleolithic diet, Stone Age diet, hunter-gatherer diet, and caveman diet.

objective
The goal of a paleo diet is to return to a mode of eating more similar to that of early humans. The reasoning for diet is that the human body is genetically incompatible with the modern diet that emerged from the advent of agriculture, an idea known as the "mismatch hypothesis."

Agriculture changed what people ate and established dairy, grains, and legumes as additional staples in the human diet. According to this hypothesis, this relatively late and rapid change in diet exceeded the body's ability to adapt. This incompatibility is believed to be a contributing factor in obesity, diabetes, and heart disease today.