Call it Paleo, call it Primal, for the most part you see many in either lifestyle poo-pooing endurance activities as unnecessary. Personally, I don't do endurance type activities because I really don't like doing them. Perhaps if I was better suited to doing them I would, but I am not. I also don't recommend clients do them unless they like to do them. More than any other criteria, your physical activity should be something you like to do, that way you do it often. However, I feel the Paleo and Primal crowds aren't using very good logic when they say endurance exercise is unnecessary. Is slamming in to a 300lbs lineman necessary? Is lifting weights at an explosive pace with terrible form necessary? For the most part, any sort of physical activity that doesn't involve you trying to attain food or procreate is unnecessary, so why try to exclude a group just because their mode of exercise isn't your cup of tea? Let's take a look at how the benefits of a Paleo diet translate in to performance benefits for endurance athletes.
Many people are confused with what a Paleo diet is and what it can do for them. Part of this can be blamed on the original message insinuating that if a food wasn't consumed regularly by your ancestors then it wasn't good for you and part of it can be blamed on people currently pushing Paleo that don't really know why it works. Paleo does not mean that any food or environmental factor that has come in the last X number of years is necessarily harmful, there are many examples to the contrary. Olive oil and broccoli are relatively new and are great for health as evidenced by the ample clinical research supporting both.
One of the biggest examples occurred millions of years ago when some of our herbivorous ancestors climbed out of the trees and began scavenging on the DHA rich carcasses left by carnivorous land animals. Organ meats rich in DHA provided a nutrient that is vital for human brain development, and is potentially one of the primary reasons we branched away from other primates and developed a much better brain. If this had never happened, certainly it would be seen as missing out on something that was a complete game changer for life on the planet.
However, on the flip side, many critics also create a logical fallacy. The fallacy on the other side of the fence is that since we have been eating something for the last 30,000 or so years that it is a healthy food. Look at the diseases killing humans today: Diabetes, heart disease, cancer, and Alzheimer's disease to name a few. Few of these diseases affect younger people, they are called chronic diseases of aging because you get them in your 40s, 50s, and beyond. Since these diseases don't typically affect your ability to reproduce and don't kill you before you can reproduce, you can't logically assume they are healthy unless your goal in life is to live to the age of 30, have 3 kids, and then die.
So then why should you be eating a Paleo diet? Let's take a look at the primary reasons, the proteins in grains, legumes, and dairy. The proteins in grains(1), legumes and dairy are immunogenic, meaning they elicit an immune response. In a healthy person without celiac disease this doesn't mean they are necessarily toxic. Look at hay fever. Pollen isn't toxic, it just elicits an immune response that gives you itchy eyes, causes you to sneeze and cough, and gives a headache. Does that mean not being able to see or constantly sneezing is something you want to do all day long? It would certainly affect your performance. Ironically, seasonal allergies as well as most other autoimmune diseases are linked to intestinal permeability(2) and many resolve on a Paleo diet.
However, therein lies the problem with the immune response to the proteins in grains, legumes, and dairy; the symptoms can range from headaches to gastrointestinal flares to metabolic dysfunction and can affect any system in the body. In fact, a lot of people have no idea they have this response until they completely remove them from the diet for a couple of months because their body has become adapted to the constant firing of the immune system and the low grade inflammation accompanying it. However, there are quantifiable things going on in your body that you may not be aware of.
When these proteins interact with the intestinal wall, they can cause intestinal permeability. Intestinal permeability is a fancy way of saying that your gut is leaking it's contents in to your bloodstream. By releasing a protein called zonulin, proteins found in grains, legumes, and dairy(Especially gluten) may dissolve the tight junctions between the cells that separate the contents of your digestive tract from your blood. This process is well known in people with celiac disease, but studies on intestinal tissue taken from healthy people indicates that it may happen in everyone who consumes gluten, it just takes longer to repair in people with celiac disease(3). In addition, zonulin is known to regulate the tight junctions in the lungs(4, ) and blood brain barrier(5). Since zonulin from the gut enters the circulation, this means it is free to interact with the tight junctions in these areas, potentially compromising brain and lung function by increasing their permeability to toxins.
This can lead to some pretty serious performance consequences. Obviously poor brain or lung function will have a big impact on performance in endurance sports. An increase in airway infections will also negatively impact training. However, one of the bigger impacts has to do with glucose utilization and insulin sensitivity.
Lipopolysaccharide(LPS) is a component of the cell membranes of bacteria found in your gut. When it enters your bloodstream, your body sense it is under attack. As a result, your immune system fires off and produces inflammation that signals your muscle and fat tissue to become insulin resistant. This spares glucose for the immune system to fight off the attacker, which isn't even really there. In addition, your immune system signals your liver to start dumping glucose in to the blood to help provide more glucose to the immune system. This is one of the reasons fasting blood glucose is high in diabetics, even if they haven't been eating carbohydrates.
Now think about that from an endurance performance perspective. You train hard which empties out your glycogen stores and burns some fat, but when you recover and eat some carbohydrate from grains you fire off the immune system. This causes your immune system to consume some of the carbohydrate you take in to fight off the infection caused by what you are eating. In addition, your muscles and fat tissue become insulin resistant so they aren't getting the energy they need to get ready for your next training session until the immune system clears the mess you created with what you chose to eat. Maybe performance isn't affected immediately because you consume so many carbohydrates, but over time you are causing progressively more damage to your digestive tract and metabolism by consuming more grains. Couple that with the fact that you are training hard which will compromise your immune system further. Also, if your liver is constantly called upon to pump glucose in to your bloodstream, cortisol may increase due to gluconeogenesis. I think all of these issues warrant some attention from the endurance sport crowd given how hard they train and how many events they participate in annually.
Before I go, let me preface what I say with a caveat. We are all different, each and every one of us. Some of us may be able to eat dairy, some may not. Some of us may be able to eat a lot of grains, some of us a few, some of us none at all. Unless there has been a 2-3 month period in your life where you've completely abstained from grains, legumes, and dairy you have no idea whether or not they are affecting your health and/or performance. That's why you should just give it a try, replace grains with dextrose, potatoes, or other tubers. If you or anyone in your family has Type 2 diabetes, heart disease, get frequent respiratory infections, or experience any form of autoimmunity I would strongly suggest you look in to the Paleo diet, not only from a performance perspective but also for general health as these conditions are associated with intestinal permeability.