The main differences between the two is the philosophies behind it, and how they are designed to work. First and foremost, it is important to realize that Paleo does allow carbs, just not grains and legumes (or anything that grows underground).
- Is a ketogenic diet. It puts your body in a safe version of a fasting state so that your body turns fat into ketone bodies. Ketone bodies cannot be reassimilated to fat so unused ketone bodies are urinated out.
- Emphasis is on both protein and fats. Protein is there to help protect your muscle mass, and fat is used to provide some additional energy.
- Is designed as a temporary diet to help you lose weight, it is not intended for prolonged use.
- Is based on what scientists believe the average paleolithic man ate. This includes berries and easily accessible fruit/vegetables as well as meat.
- Emphasis is on avoiding processed foods and foods that are likely to cause digestion problems. This includes grains (like wheat), tubers (like potatoes), and legumes (like beans).
- Is designed as a way of life diet, or in other words a sustainable diet you can use for the long term.
There are some commonalities between the two approaches, such as the emphasis on meat as a protein source. However, Paleo tends towards whole foods and grass/natural diet fed meat and Atkins makes no distinction. While Atkins does not allow carbs which would take someone out of ketosis, Paleo does allow carbs.
Anyone who exercises regularly will need the following for a healthy diet:
- About 1g protein / lb lean body mass. This is both for the better thermic effect of food (i.e. it burns more calories digesting it), and for restoring muscles that have been torn down by exercise.
- Carbs on workout day. This is a minimum, as it helps restore your glycogen levels to help you recover more quickly.
- A combination of saturated and mono-unsaturated fats. Fat is used for energy, but it also carries with it essential fat-born vitamins. NOTE: I did not include poly-unsaturated fats which are man-made and cause health issues over the long term.
How you proportion those depends on your daily caloric needs, but it is safe to split the remaining calories after you have your protein evenly between the carbs and fat. This is very possible on the Paleo diet, but due to the way Atkins is designed it is not possible on that diet. You will likely need to alter how you exercise on Atkins to ensure you do not burn muscle.