Study of The Effects of The Transition to a Low-carbohydrate High Fat Diet

There have been many studies conducted over the years that analyze the effects of lowering dietary carbohydrates on health and exercise performance. This study analyzed the effects of altering diets from “the habitual Western based diet (WD) to a very low-carbohydrate high fat diet (VLCHF) over 4 weeks” on performance and the physiological responses during High Intensity Interval Training (HIIT).

To conduct the study 18 moderately trained males were examined over the course of 4 weeks. They were separated into two groups: 1. A very low-CHO high-fat group and 2. A habitual mixed Western diet group. A VLCHF diet restricted the carbohydrate consumption to 20-50 g/d and replaced most of the lost calories with fats and maintains a low to moderate quantity of protein. The males were aged between 18 and 30 and were engaged in low endurance, non-competitive regular physical activity of at least 3 sessions/week and all participants have no experience with VLCHF diet. Pre and post experiment a maximal incremental treadmill test (GXT) was performed to identify VO2 max. The treadmill started at 7. 0km/h and increased by 1. 5km/h every 4 minutes. The HIIT sessions were conducted throughout the 4 weeks and sessions were separated by 48 hours. These sessions involved warming up for 10 minutes at 60% of their VO2 max. The main session consisted of 5 high intense, 3 minute reps at 100% of VO2 max. Recovery was 90 seconds. HIIT sessions lasted 34 minutes. Sessions were conducted in the morning at similar times each day, (give or take 30 minutes) at least 3 hours after their last meal.

Tests were conducted in a thermally controlled environment where body mass composition was determined, and a capillary blood sample was taken before all exercise interventions. Participants were also asked to participate in 3-5 sessions of primarily endurance based, non-supervised training, alongside recording their heart rate throughout these sessions. Participants were provided with meal planning recipes and suggestions by dietitians and assistance was provided throughout the test when it was required by participants. Beginning 5 days before the intervention all food quantities consumed was recorded daily. The consumption of alcohol before and during the intervention was prohibited as well as the consumption of caffeine before laboratory sessions.

The results showed that overall there was no adverse effects on performance in the GTX or HIIT of participants consuming the VLCHF diet. Also in the VLCHF group it was found that substrate oxidation changed significantly. Levels of fat oxidation and blood lactate concentration increased in the VLCHF diet group. The findings in this study challenge the presumed necessity of a high carbohydrate diet for high intensity exercise. Some research suggests that it may require several weeks for noticeable adaptations to occur with the VLCHF diet. A study that recorded the results of relative power during a 6 second sprint improved after 12 weeks of adaptation the VLCHF diet. The short period of time that the study was conducted over is a limitation of this study as it does not give participants a chance to fully adapt to the diet. Another limitation to this study is that the diets were not strictly monitored. The participants were responsible to monitor their diets appropriately. The food consumed throughout the study was also not isocaloric, meaning each meal did not have similar caloric values.

In conclusion the study aimed to determine the effects of altering from a regular Western based diet to a VLCHF diet over 4 weeks on performance and physiological responses during HIIT. The researchers found that throughout the 4 weeks there was no adverse effects on performance in the high intensity training in either groups but levels of fat oxidation and blood lactate concentration increased in the VLCHF group.