The following is a summary of a study I did for Cycling Plus Magazine that investigated how a three-week low carbohydrate diet influenced metabolism and performance of three amateur cyclists. The full study is available here.
Fat burning
The participants recorded all their food intake using an app throughout the study. The goal was to limit carb intake to 10% of total energy intake. However, despite their best efforts, the participants could not achieve this - their actual carb intake was 23-26% of total energy intake. Although the participants did not follow a ketogenic diet, the data suggest a ketogenic diet may not be necessary to markedly increase rates of fat oxidation during sub-maximal cycling.
As with previous low carb studies, the low carb diet in my study noticeably increased fat oxidation during sub-maximal cycling. For example, two of the participants’ peak rates of fat oxidation more than doubled, similar to the values in the previously mentioned 1983 study.
Diet and weight (fat) loss
The low carb diet promoted positive dietary habits. For example, the participants avoided energy-dense snacks, such as crisps and chocolate, and alcohol intake was minimal. This change in eating habits meant the cyclists consumed less calories during the low carb diet, which resulted in two participants reducing their body fat.
Performance
Every week the participants performed a 20-minute cycling time-trial (TT) to assess performance. The increased fat burning capacity, and lower body fat outcomes did not translate into improved TT performance. In fact, the data indicated two participants performance decreased* during the low-carb diet.
*This was a case study (3 participants), as such there was not enough data to establish if the changes in TT performance were statistically significant.