Research Study: Fat Loading Versus Carb Loading and Performance

If you’re at all involved in the endurance sport field, you may have already heard about a practice called ‘carb loading’, where you take in a large volume of carbs after performing carbohydrate depletion workouts, hoping to maximize how much energy is stored in the muscle cells.

The idea is that by doing so, you can help prevent fatigue from occurring while you’re out there performing the race or whatever the event may be.

Now though, researchers are starting to look at an alternative approach – fat loading. Here’s what this entails.

Study Design

The study had seven cyclists undergo a two week adaptation period to three different diets. One was a 14 day high carbohydrate diet, the second was a high fat diet, and the third was a high fat diet that included a 2.5 day carbohydrate loading period at the end.

The meal before the cycling session took place was the same in composition as the preceeding diet, thus eliminating the effects of a common pre-workout meal.

All athletes were asked to follow a normal standardized diet before the study took place, so they were going in under the same circumstances.

The exercise that was performed lasted aproximately five hours and included a 15-minute trial, which was aimed to measure the peak fat-oxidation rate, followed by a 100 km trial.

During the exercise sessions, sports bars and a 5% carbohydrate solution were taken in.

Results of the Study

The results of the study indicated that none of the diets had any statistically significant impact on the fifteen minute performance with the exception of the high fat diet with carbohydrate loading period having a slight advantage in terms of total distance covered compared with the straightforward high fat diet.

When looking at the 100 km-time trial period, both of the high fat diet scenarios decreased the dcline in power output demonstrated with the high carbohydrate condition.

To put things in perspective, the high fat diet with carbohydrate loading demonstrated a 1.3 fold greater power output compared with the high-carbohydrate diet.

Metabolic Changes

Outside of performance related variables, the metabolic changes that were seen with the higher fat diets included lower plasma insulin concentration before exercise, a 10-20% higher plasma-glucose concentration, and a 2.5-2.9 fold increase in peak fat-oxidation rate.

Conclusion

Therefore, from this study we can see that high-fat diets can be used to promote optimal performance as well as a higher rate of fat oxidation for endurance athletes.

Practical Implications

The practical implications of this show us that for those who do not tolerate carbohydrates that well – you’re either insulin sensitive or have troubles moderating volume of carb-heavy foods consumed, a high fat diet can be a good solution if you are primarily involved in aerobic type of training.

In conclusion, high-fat dietary conditioning increased fat oxidation, and although the main effects were not statistically significant, there was some evidence for enhanced ultra-endurance cycling performance relative to high-carbohydrate.

Reference:
Hopkins, WG. (2002). Effects of high fat and high carbohydrate diets on metabolism and performance in cycling. Metabolism. Jun;51(6)678:90.