Non-Ketogenic Low Carbohydrate Diets

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This article focuses on Non-Ketogenic Low Carbohydrate Diets (NKLCD), rather than Ketogenic Diets. The characteristics of NKLCD and ketogenic diets are significantly different, and therefore they must be considered separately.

1 Potential Advantages of Low Carbohydrate Running

  • Your body has limited stores of carbohydrate (glycogen), typically around 2,000 Calories, but for most people there is a virtually unlimited supply of body fat. A pound (0.5 Kg) of body fat contains around 3,500 calories, enough for 30+ miles (50+ Km). So most people have more than enough body fat to provide the Calories to run a 100 mile (161 Km) race without needing any fueling. Even if it's not possible to exercise while just burning body fat, any shift to burning more fat will help preserve the limited carbohydrate stores.
  • The desire to lose weight is prevalent, so burning body fat as fuel would improve weight lost.
  • Training with a low carbohydrate intake improves subsequent glycogen storage when carbohydrate intake is increased. This cycle of low carbohydrate followed by high carbohydrate is a technique for Carbohydrate Loading.
  • Restricting carbohydrate may help control diabetes and improve blood glucose control.

2 Potential Pitfalls of Low Carbohydrate Running

  • Burning fat requires about 6% more oxygen to get a Calorie of energy than carbohydrate. This is a major problem with fat metabolism for exercise as you become about 6% slower. (ATP yield per mol O2 is 5.65 for fat and 6.0 for carbohydrate.)
  • The time to reach peak fat metabolism is about 30 minutes, compared with 3 minutes for peak carbohydrate metabolism. This means that it takes far longer to 'warm up' for fat burning.
  • The amount of energy that can be produced by a given amount of muscle from fat is about half of the energy that could be produced from carbohydrate (2.7 v 1.4 mmol ATP sec-1 kg-1).
  • The brain normally requires glucose for fuel and a drop in blood glucose can impair mental functioning, and in extreme cases can result in a coma. (Some parts of the brain can burn ketones which are produced from fat, but this requires a ketogenic diet.)
  • Restricting carbohydrate intake tends to reduce the Muscle Glycogen stores.

3 Running Performance and Low Carbohydrate Diets

Studies that look at the impact of a short term change in diet have consistently shown that a Low Carbohydrate Diet produces exercise impairment. These studies are the basis of the belief that exercise requires a high carbohydrate intake. However, proponents of low carbohydrate diets suggest that there is an adaptation period required for the body to metabolize fat efficiently. While there are a small number of studies on exercise performance and a Ketogenic Diet, I've only found one that looks at a Non-Ketogenic Low Carbohydrate Diet.

4 See Also