Today’s topic is fat loading. Fat loading! Sounds like a dream come true! I envy the athlete who got to be in the research study for that one. When I first heard this my left brain immediately scoffed and dismissed it, but then my right brain said, “Hey David, fat is the primary source of fuel at lower intensities. Would this help for longer distance races?” So, I took a look at the research.

A 2003 study published in Medicine & Science in Sports & Exercise took 11 athletes and had them take in a high fat diet of 53%, and the other group with a low fat diet of only 17% for 5 weeks. Glycogen content was slightly lower in the high fat athletes, but not considered statistically significant. VO2 max was not statistically different between the two groups. Cycling 20 minutes all out, followed by a half-marathon, showed no statistically significant performance decrease in the high fat diet.

Now, I’d like to point out that I am a firm believer in statistics and margin of error, and something being statistically significant or not statistically significant. But if you were to take the times of the top 5 finishers in a Olympic-distance triathlon, and their times are likely only separated by 1 minute or less, and run a statistical analysis on those 5 times, the result would be that there was no statistically significant difference in their times. But, the fact is 1 person was still faster than the other 4. A race director is not going to buy the argument that the second place guy was within the statistical margin of error, and should therefore share first place. So I’m not trying to dilute the importance of statistical analysis but in this study, VO2, glycogen stores, and performance were all just a bit higher in the low fat vs. high fat, although within the margin of error and so in the scientific world there was no difference between the two groups. Perhaps no benefit from fat loading but there was certainly no disadvantage in this study.

In another study from Australia looked at 7 cyclists that took in either a high carb or high fat diet for 6 days, the high fat diet taking in 4.5 times the amount of fat compared to the high carb diet. The researchers found that although there was no difference in performance, the high fat diet used more fat for fuel, which is exactly what you want to train your body to do, specifically for long-distance events.

Finally a 2003 study from the University of Otago in New Zealand seemed to indicate some possible benefit from fat loading on endurance racing. Again, 7 cyclists took in either high fat or high carb diets over a 14-day period followed by a 15 minute time trial and then a 100k (62 miles) time trial. There was a slight decrease in performance in the high fat group on the 15 minute time trial.  But in the 100k time trail, there was a slight increase in power and performance in the high fat group, although the researchers concluded that it was not statistically significant. As in the Australian study, fat was used more for fuel in the high fat group. The researchers concluded that although the main effects were not statistically significant, there was some evidence for enhanced ultra-endurance cycling performance relative to high-carbohydrate.

My opinion on this is that I am not qualified to have an opinion. Seriously, it tends to go against conventional nutrition strategy but convention has been challenged many times in sports physiology to prove what we thought was wrong. What I do know is that no study has shown any performance improvement in fat loading over short distances and only possible improvements over long distance. However, all the studies I looked at failed to tell me the effect on an athlete’s body composition from the fat loading. Did this increase their overall body fat? I can’t imagine that it would not have had some effect on body composition.

Remember that these tests were performed on stationary bikes, so although the performance gains may have been neutral to slight on a stationary bike, any weight gained would not affect the study. Whereas, when cycling outdoors, where you are forced to accelerate your own mass, a 2-pound gain from fat loading would in fact have a negative effect on your performance. I say the jury is still out on this one, there just isn’t enough conclusive proof to do it. If you do choose to try fat loading remember that in the two studies that showed possible benefit for long distance racing, fat loading only took place for the 6-14 days prior to the time trials. Don’t go out and perform a 6 month fat loading plan.

David Warden is a 3-time USAT All American and Elite Coach with Joe Friel's TrainingBible coaching. His work has been published in Triathlete and USA Triathlon Life magazines. He is the former Vice-Chair of the USAT Rocky Mountain Region, and the host and producer of the #1 triathlon podcast, Tri Talk and part owner of  www.powertri.com.