No one miracle diet can achieve all things.  Before starting a diet, it's important to understand the impacts of the diet, who is the diet good for, what the studies show regarding the diet, and what the side effects are of the diet.  The impact of cutting calories and removing certain nutrients for the diet can cause serious health implication and lead to serious illness and disease if not managed correctly.

The "Ketogenic diet" (KetoDiet) is a hot topic at the moment due to quick weight loss results and improvements in endurance based sports performance.   However, recent studies have found that a KetoDiet is not a great option for strengths, speed and power athlete looking to improve their performance.  [1,2]

Many endurance athletes have found success with KetoDiet because fat provides more energy than carbs in an aerobic driven environment. [3]  This is not true for the anaerobic energy system because the Krebs cycle, the primary energy generator in the anaerobic energy system, produces significantly less energy when catabolising fat or protein when compared to carbohydrates (CHO).

The argument to “become a fat burned” or that “fat is a more efficient fuel source” is only true in an aerobic setting, not an anaerobic one.

If you are trying to improve athletic performance in high-intensity sport, you might want to give the Ketogenic diet a miss.  Often a low carb diet trends towards a high protein diet, but the KetoDiet restricts protein intake because the human body can convert protein into CHO through a process called glycolysis. When the body is running low on carbs and protein, it start to manufacture ketone bodies as a source of emergency fuel. According to lead researcher, Dr. Edward Weiss, this is an “emergency backup system that allows us to survive when we are at risk of starvation.” [1]. Weiss is concerned that a body running on empty may not be able to work at full capacity, which is essential for athletes competing in high-intensity sports.

You might be thinking that low energy production is only a concern for elite athletes or physically active people who train multiple times a week with high intensity intervals training (HIIT) classes like CrossFit and F45, but you would be wrong.  But for someone with low fitness, they use this same energy system to get up the stairs.  Most people use their anaerobicenergy system without evenrealising it.  If you are pushing your body to a point where you are gaspin for air and and you need to stop and take a short rest, chances are you have activated the anaerobic energy system pathways.  When the demand for energy increase beyond your aerobic capacity your body switches on the anaerobic energy to meet the increased energy demands.  Unfit people activate this energy system long before those who are fit.

"Short-term low carbohydrate, ketogenic diets reduce exercise performance in activities that are heavily dependent on anaerobic energy systems”. "These findings have clear performance implications for athletes, especially for high-intensity, short duration activities and sports.” [2]

The KetoDiet impact the anaerobic energy system which is used to produce high levels of energy for a short intense period of time.   Track and field sports like sprinting, shot put, and triple jump depend on this energy system.

Research from Saint Louis University compared the performances of 16 men and women who followed either a KetoDiet or a high carb diet. They found that after following a KetoDiet, study participants did not perform as well as anaerobic exercise tasks. [1]. A separate 2018 study also found that short-term low-carbohydrate, KetoDiet reduce exercise performance in activities that are heavily dependent on anaerobic energy systems. These findings have clear performance implications for athletes, especially for high-intensity, short duration activities and sports. [2]

This second study found that low-carb diets (<50 g/day and <10% of energy from carbohydrates) resulted in 7% lower peak power and 6% lower mean power during the Wingate Test when compared to a high carb diet ( 6-10 g/kg/day carbohydrate).

“So, if you limit carbs, you might find yourself just not eating that much. If you eliminate most food options, you may just be losing weight because you are cutting calories”  The KetoDiet can be helpful for those who have epilepsy as research has shown that ketone production limits seizures but concludes that “unless there are compelling reasons for following a low-carb diet, athletes should be advised to avoid these diets."[1]

A seperate study utilised recreationally trained subjects and found that a low-carb diet significantly reduced strength as measured by a three-set squat repetition for max repetitions at 80% 1RM.  "The carbohydrate restriction program caused a significant reduction in the number of squat repetitions performed” [4].  

Two other studies utilised cycle ergometerto measure anaerobic power output in healthynon-highly trained subjects and found drops in mean and peak power.[5,6]

There is some limitation in all of these studies as many would argue that adequate KetoDiet adaptation was not achieved in the short time frame of the studies. Although, the results suggest low-carbohydrate diets impair intense, short-term physical activities.  These findings have clear performance implications for athletes, especially for high-intensity, short duration activities and sports and until research can prove otherwise, it makes sense for strength and power athletes to avoid the KetoDiet.

REFERENCES:

  1. Food for thought: Ketogenic diets reduce athletes' anaerobic performance, study finds, Weiss, E. et al., 2018

  2. Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. Wroble, KA. et al, 2018

  3. Endurance athletes who 'go against the grain' become incredible fat-burners. Ohio State University, 2015

  4. Effects of Carbohydrate Restriction on Strength Performance. 1999

  5. The effect of  a  low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal  exercise. Langford, J. Et al. 1997

  6. Endurance capacity and high-intensity exercise  performance responses to a high fat diet. Fleming, J. Et al. 2003


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