High Fat Diets for Performance
Hi Fat & Low Carbs; Is it Viable for Performance?
This article explores the alternative of performance while implementing a low carbohydrate diet. Before we look into a few studies its important to iron out some of the finer points. Firstly this article is investigating the effects of low carbohydrate diets on aerobic/endurance performance. Next we need to confirm what constitutes a low carbohydrate diet. In this case we are looking at low carb/high fat diets where fats contribute to >70%, proteins <30% and carbohydrates <5% of the participants daily caloric intake.
Without getting too deep into how your food breaks down to become energy (another article perhaps!), you need to understand that apart from alcohol, carbohydrates are the easiest marco-nutrient to break down to be used for energy, followed by fats and finally by protein. Traditionally athletes have used high carbohydrate diets in order to have an excess of glycogen (the energy substrates of carbohydrates). An outstanding problem with this is that glycogen can only be stored in relatively small capacities and as those energy stores decrease with prolonged bouts of exercise, performance can also decrease. One of the potential benefits of using a high fat diet is that as you deplete your body of glycogen, your primary energy source will switch to fat oxidation and FAT can be stored more abundantly in the body (both from the calorie dense foods we eat and fat that was have stored already).
Effects on a general population:
A group of regular individuals underwent a treadmill endurance test to determine VO2 max (the maximal amount of oxygen an individual can utilize during exercise), while also tracking time to exhaustion. They then utilized a 6-week low carbohydrate, high fat diet before retesting. Its important to note that the calorie count was set at a deficit for potential weight loss and no other training was had during these 6 weeks. At retesting the participants averaged a weight loss of 10kg, and even when wearing backpacks with the weight they lost, their aerobic efficiency was elevated and time to exhaustion was increased by a staggering 47%. Although time to exhaustion was greatly increased, V02 max remained the same. While these results speak for themselves, many people know that the untrained population will generally have highly elevated initial results when undertaking a new program so its important to investigate a trained population also.
Effects on an athletic population:
To investigate the athletic population, a group of elite level cyclists performed two tests; an aerobic endurance test at 60% of V02 max to find maximal time to exhaustion and a second test (30-second Windgate test) at 90% of VO2 max to determine supramaximal muscle power. After implementing a low carbohydrate, high fat diet for just 2-weeks, the athletes showed an increased of approximately 50% in time to exhaustion and no drop in maximal muscle power output. Like the general population tests, V02 max remained consistent between base and end testing.
What do these results show us?
Significant fat loss in untrained individuals
Significant increases in total time to exhaustion for both groups
No loss in muscular output
V02 Max remained constant across both populations
The fact that V02 max didn’t increase across either group indicates that the low carbohydrate, high fat diet won’t directly affect an individual’s ability to utilize oxygen during exercise. However, by depleting the body of carbohydrate stores, thereby prompting it to use fat oxidation as its primary source of energy, the significant increase in time to exhaustion can be attributed to the greater storage capacity of fats.
Possible health benefits and risks:
Unfortunately there isn’t a huge amount of information on the long-term side effects of a low carbohydrate, high fat diet. It has however been determined that over short time periods (up to 12 months), the diet can be very effective for fat loss. It has been shown to significantly improve triglycerides and insulin sensitivity, particular in subjects with a high risk of cardiovascular disease or diabetes. It has also been shown that over short time periods, there is no negative impact on bone density or health, even in adolescent populations.
References:
Cook, C., & Haub, M. (2007). Low-carbohydrate diets and performance. Current Sports Medicine Reports, 6, 225-229.
Crowe, T. (2005). Saftey of low-carbohydrate diets. Obesity Reviews, 6, 235-245. 245.
Phinney, S. D. (2004). Ketogenic diets and physical performance. Nutrition & Metabolism, 1(1), 2. doi:10.1186/1743-7075-1-2
Written by Nevin Mills - The Strength Institute of Western Australia
