I have recently started working with a few endurance athletes who want to improve body composition while training for Ironmans.  My approach in a nutshell: paleo diet with a focus on adequate fat intake and carbs under 100g a day, although I prefer 50g a day. The key is to get people to REPLACE carb calories with fat and protein calories, rather than eating more protein, less carbs, and becoming calorie restricted and hungry all the time because the fat intake is low.  It's hard for many people to do, as they are trying to let go of the "fat is bad" mentality that we have grown up with. I find it much easier to convince people they should eat lower carb than it is to get those same people to replace those carbs with fat. But the evidence is there: eating a low carb, high fat, and moderate protein diet is very effective for losing body fat. 

When I want to drop a few pounds, I make sure 65-75% of my calories come from fat, and I eat less than 50g of carbs a day so I get into mild ketosis. But, I am not doing any kind of endurance training and haven't done any for the last year. Because of that, I have had some ideological struggles about what to prescribe for my clients that are endurance athletes, as I want to make sure that I am addressing their nutritional needs while also minimizing the deleterious effects of excessive exercise on their health and body fat levels. 

What I have been struggling with the most is my recommendations for carbohydrate levels for these athletes. I really believe that under 50g a day is optimal for losing body fat, improving cardiovascular health, reducing inflammation, and minimizing hunger. However, I worried that it wasn't "enough" carbs to fuel workouts. I also struggled with this personally, as I would like train for a triathlon again but do not want to increase carbs, as I really love being lean and I believe that a low carb diet is best for optimal health and longevity. 

The Paleo Diet for Athletes by Joe Friel and Loren Cordain is NOT necessarily low carb. They take the position that carbohydrate needs are higher for endurance athletes, but that you should get those additional carbs from paleo foods (yams, fruit) rather than neolithic foods (grains).  This definitely works from and athletic performance angle, and also reduces inflammation and helps counter oxidative damage through high consumption of vegetables and fruits high in antioxidants, but what about people that want to lose body fat? Will a higher carb paleo diet work for them? I am not sure. 

Yesterday I re-read this article in Nutrition and Metabolism that discusses the use of VLCKDs (Very Low Carb Ketogenic Diet) in athletes. The author reviewed previous research and reported on two studies he had conducted. In his review of previous studies, he found that the most common result was that a VLCKD reduced athletic performance, but that those studies were only a few days-1 week in length. His own studies were 5-6 weeks in length and showed that there IS a decrease in performance in the first week of a ketogenic diet in athletes and sedentary people, but that all markers return to previous levels after that short period of adaptation. Here is a chart from a 5 week study the author performed on elite cyclists:

Exercise parameters of MIT EKD study [15]

VO2max (LPM) Exercise VO2(LPM) Exercise RQ Endurance time (min)

Baseline 5.1 3.18 0.83* 147
EKD-4 5.0 3.21 0.72* 151

LPM, liter per minute * P < 0.01
Phinney Nutrition & Metabolism 2004 1:2   doi:10.1186/1743-7075-1-2

After I re-read the article, I started to think that there was a better way to use the Paleo Diet with athletes. If an athlete wants to see improvements in body composition, or at least not GAIN body fat while training for endurance events (very common, especially in female athletes), then utilizing a VLCKD may be appropriate. 
I unexpectedly found more information on this topic today while looking through the textbook I am using to study for my International Society of Sports Nutrition (ISSA) certification exam. I have had the book for weeks, but was not at all inclined to open it as I was certain in contained the traditional low-fat/high carb dietary advice you get from most sports nutritionists and dieticians. For some reason, I chose this morning as a good time to crack it open, and too my surprise, it contains an entire chapter on VLCKD for athletes! Even more surprising, it looked upon this diet FAVORABLY and provided a good amount of information on how a VLCKD can improve body composition, cardiovascular disease risk factors, cholesterol numbers (they even talked about large, puffy LDL versus small, dense LDL), fasting and postprandial (fed state) triglyceride levels, and inflammatory markers while of course also reducing the risk of Metabolic Syndrome, Diabetes, and obesity. Here are two quotes from the summary paragraph:

The dramatic change in macronutrient distribution associated with restriction of carbohydrates results in robust and powerful metabolic adaptation that improves a person's ability to mobilize and utilize noncarbohydrate energy sources. 

In conclusion, studies support the notion that short-term VLCKDs are safe and effective in terms of promoting weight/fat loss, improving metabolic and cardiovascular risk factors, and are compatible with a physically active lifestyle.

I jumped up and down and clapped my hands like a little girl getting a pony for her birthday when I read that! It has greatly reinforced my position that there are two ways to use the Paleo Diet for athletes: one for sports performance and one that encourages positive changes in body composition. Any athlete can use either approach, depending on what their goals are and where they are in the season. For my athletes that are in the early part of their training for summer Ironmans, I feel more confident in prescribing 50g or lower of carbohydrate per day. That would be the time to use a VLCKD and allow time for adaptation. Once adapted, the athlete should see a loss of body fat. When their desired weight has been reached, they can experiment with adding in more carbohydrates from paleo sources while noting any positive or negative change in how they "look, feel, and perform" (as Robb Wolf would say!). 

I will personally take this to heart as I begin to formulate a plan to train for either a sprint or Olympic distance triathlon this summer, and will continue with my current VLCKD as I ramp up the training volume. The only concern I have is that the one thing that does seem to suffer when using a VLCKD is sprinting and short, high intensity effort. As that will be my primary training approach, I wonder how that will affect me. High intensity training is miserable enough, without doing them all while feeling like you don't have any energy. It's a giant experiment, and I am willing to take it on! I will report back as things develop.