What is the Keto Diet and why is it popular?
The ‘Keto diet’ is still a popular weight loss diet and some would say for good reason. The ketogenic diet consistently gets good short term weight loss results and can even be medically prescribed in certain conditions, such as epilepsy. Due to a change in fuel usage by the brain, from glucose to ketones, this can help reduce fitting episodes; it was indeed in this setting that much of the early development and research into the ketogenic diet was undertaken. But what exactly is ketosis? What are ketones? How do we achieve this state? And is there anything that gives this kind of a diet an advantage in either a weight loss or performance setting over other dietary strategies?
What is nutritional ketosis?
When we talk about ketosis in this context, we are talking about nutritional ketosis, this is not to be confused with ketoacidosis, which is a dangerous metabolic condition caused by medical issues such as diabetes. In a state of nutritional ketosis our body has switched from using glucose, which we derive from eating carbohydrate and glycogen stored in the liver, to ketones as a primary source of fuel. This is achieved by severely restricting carbohydrate intake, often to less than 50g per day.
As the body’s glycogen levels are reduced, the body still needs to maintain a certain level of blood glucose to survive as certain essential functions still require glucose as an energy source, however as the brain places a big demand for fuel (normally preferring glucose) and can’t use fatty acids (from body fat or dietary fat intake) as they can’t pass the blood-brain barrier, fortunately, our bodies have evolved to be able to convert fatty acids into ketones which can pass this ‘barrier’ and be used as a fuel by the brain.
Fatty acids are converted to ketone ‘bodies’ in the liver to fuel the brain, and many of our other tissues can use fatty acids as a fuel under high oxygen, aerobic conditions. Fortunately, we can also create enough glucose, from amino acids and the glycerol which are a component of dietary fats, to perform the basic functions that glucose is essential for. The conversion of amino acids to glucose, through a process called gluconeogenesis, can actually take place at quite high rates when required, so in order to stay in a state of ketosis, protein intake is often kept at no higher than 30% of the total daily calorie intake.
A background level of ketones in the blood is almost always present and are important for fuel during periods of fasting, however full ‘keto-adaptation’ can take several days to take hold and during this period of adaptation it can be very tough especially mentally as the brain is being deprived of fuel in the short term. After people have become adapted, they generally feel more energised and have less brain fog. But considering all these early negative effects, and the fact that it requires a restricted diet that avoids many foods that can pull a person rapidly out of ketosis, is there actually any benefit of being in ketosis?
What are the benefits of ketosis and the Keto Diet?
From a fat loss perspective keto diets are effective, however the fact we use fat as a primary fuel source is not actually the main reason. Keto diets have shown that, due to the high protein and fat content, that people tend to consume less calories and ultimately the energy deficit created is the driving factor of keto, and for that matter, any weight loss nutritional strategy. But what about a keto diet compared to a diet that contains carbohydrate?
Some studies have suggested yes, however when studies have matched for both protein intake and overall calorie intake, there appears to be no difference in fat loss between low and higher carb diets, however for those who don’t want to track calorie intake then taking a lower carb approach may have a benefit in this regard.
Are there any negatives?
One negative of the low carb approach is that it will fairly rapidly reduce muscle glycogen stores especially in those who take part in moderate to high-intensity exercise. This is because glycogen can be used as a fuel in activities that have low oxygen availability (anaerobic energy production) and the higher the intensity the more reliant we become on glycogen as fatty acids cannot be converted to energy in these conditions. Therefore for those who compete in many sports, or who train hard in the gym, then cutting carbohydrate completely will almost certainly have an impact on performance.
Despite the weight of metabolic and sports specific evidence that shows why keto diets would not be of benefit for athletes, die-hard proponents of keto still insist that you can maintain performance and it may even have performance benefits. This may be true in very low demand activities where we can provide enough oxygen to oxidise fatty acids easily enough for fuel, but for most physically active people going keto will likely reduce performance and, as of yet, there is no viable mechanisms by which relying on fatty acids would offer any increased performance benefit or even be comparable to a diet containing carbohydrate.
In summary, the keto diet is an effective short-term strategy for fat loss, however, it is not necessary to remove carbohydrates from the diet in order to achieve the same effects. Long-term adherence to Keto diets will often suffer due to over restriction, leading to dietary failure. For performance, a keto diet offers no tangible benefits and much of the relevant evidence shows a decrease in performance, so for any athlete reliant on glycogen as a primary fuel, using a keto diet would be taking a big, unnecessary risk.