By now you have surely heard somebody talk about “keto”, whether it be ketones, ketogenesis, ketosis or even just the general idea of cutting carbs. More and more it seems this idea is being pitched as the holy grail and exclusive tried and true, proven method, to burn body fat. In fact, there are so many rumours and claims surrounding ketones that are being thrown around, including performance enhancement, and cognitive improvements that I think it’s high time to separate some fact from fiction.

It’s not just the general public, but the media, and even supplement companies that are often confused about these topics, and there’s a very important distinction to be made to understand the difference between ketosis and ketones. So if you’ve heard a lot about “keto” lately and want to finally clear up the confusion around the keto diet, what ketosis is and whether it’s really helpful or just hype, you need to read this article...


What Is Ketosis?

As far back as the 1970’s, a carbohydrate restricted diet became popular as a method to lose weight. However, as the public became more aware for the dangers of elevated triglycerides and cholesterol, it became wildly unpopular. Since then, there has been a resurgence of low-carb dieting especially as the incorporation of added sugar into food products has been on the rise and strongly associated with the incidence of obesity and diabetes.

However, instead of adopting balanced dieting strategies, fad diets enjoy going from one extreme to another. Fats used to be the demon, as the sugar companies convinced the public that reducing fat intake is the clear method to lose fat. Nowadays, carbohydrates are the demon everyone is trying to avoid and praising fat as a so called “super fuel”.

Ketogenic dieting is a concept where the tissues of the body will rely primarily on fat metabolism for energy if the diet is deficient in carbohydrates. By definition, a diet with less than 5% of net calories coming from carbohydrates is deemed a ketogenic diet. Maintaining this diet for several days to weeks will allow the body to drain the carbohydrate reserves stored as glycogen in order to initiate a state of ketosis.

What follows is an embedded survival mechanism inherited from our ancestors for times of starvation that prolongs life during famine. In order to sustain energy demands, fat oxidation alone is insufficient. Therefore, fatty acids are converted to ketone bodies (known as ketones) to be transported around the body and act as a surrogate energy source by most other tissues. There are 3 known ketones produced from this process called Beta-hydroxybutyrate, Acetoacetate, and Acetone and once these compounds reach a critical level, a state of nutrition ketosis is said to be achieved...

One of the easiest ways to determine whether you have reached nutritional ketosis is that people may talk to you less. The acetone on your breath creates a horrible odor that could scare all the people around you away. But assuming that’s not a deterrent yet, getting into ketosis is not as simple as it seems. When less than 5% of your net calories are coming from carbohydrates, a very large percent of the calories need to come from fats (because protein can be converted to glucose). However, it can be relatively difficult to consume large quantities of “healthy fats” (unsaturated fats vs. saturated/trans). As a result, there may be a drastic variation in the healthful impacts of the keto diet, with some keto-dieters who may actually be causing more cardiovascular harm rather than good.


Weight Management and Health

There is indeed ample evidence showing the effectiveness of a keto-diet with fat loss, especially when employing a caloric deficit. However, evidence that this method is superior compared to a balanced caloric deficit is lacking. The key of course to weight loss is being in a caloric deficit. Recent research shows that when comparing a low-carbohydrate, ketogenic diet group to a low-fat diet group for 24 weeks, the total amount of fat loss was similar between the two groups.

If the goal is purely weight/fat loss, then keto may be a fine option when used correctly. However, there does not appear to be any evidence of superior results when compared to any other calorie restricted diet and just like any diet, the selection of healthy foods is still an important aspect. Moreover, if you have any other physical or performance goals, then keto actually may not be the best choice.



There are some misconceptions about the effects of ketosis on exercise performance. The common belief is that this “miracle dieting strategy” appears to be able to do everything. Unfortunately, increasing fat burning while improving performance is not one of them. Low blood glucose is known to impair exercise performance through limiting availability of carbohydrates in the muscles. This is especially true for high-intensity exercise.

The absolute worst analogy I have ever heard is: “If carbohydrates are like gasoline, then fat is like jet fuel”. Analogies like this are what happens when people misunderstand science on both ends of the analogy. Ignoring the very minor performance differences between the engine fuel types, fat (or ketones) are not metabolized nearly as fast a carbohydrates are.

High-intensity exercise is largely driven by how fast energy can be made available. The rate at which fuel can be used is a controlling factor that determines the power of the activity. Without an adequate supply of carbohydrates, high-intensity performance absolutely suffers (read more about that here). This is why you do not hear about power athletes adopting a ketogenic diet.

What About Endurance Exercise?

What people mean by the “jet fuel” analogy is that fat is more energy dense and its metabolism can be more efficient compared to carbohydrates. Luckily for all of us, when engaging in low-intensity or long duration exercise, the body naturally switches to fat oxidation for this purpose whether you are in ketosis or not. If you are looking to engage in a type of exercise where you think total body energy would be a limiting factor, than it could be theorized that a state of ketosis would allow the body to run more efficiently, at low intensities, for longer. However, training for endurance exercise may actually be impaired under the influence of a ketogenic diet. A study with elite, olympic-level endurance athletes showed that endurance training with a ketogenic diet impaired the improvements in VO2peak, and as a result impaired any improvements in race times.

From a performance perspective, ketogenic dieting is not advisable for anyone who seeks to maximize high-intensity performance, power performance, or even endurance-training adaptations. It truly is exclusively for those looking to improve aesthetics while sacrificing any other physical benefits of training.

Another claimed benefit about ketosis has to do with a cognitive benefit as it has been reported to make you sharper and more clear minded. However, the cognitive research on ketosis is nowhere close to supporting these claims.


Keto Cognition

In many disease states, such as epilepsy and other neurodegenerative disorders like Alzheimer’s and Parkinson’s disease, a ketogenic diet has been observed to show improvements in brain health. However, the popular claim that ketosis improves cognition in healthy individuals has yet to even be studied. Nonetheless, this hasn’t stopped many people from linking the two together. Unfortunately, the mechanisms how ketosis may aid some neurodegenerative diseases have to do with correcting chemical imbalances and/or transport of nutrients into the brain. None of which would be helpful in a healthy brain.

The natural production of ketones is actually meant to be a mechanism to preserve glucose (the ideal nutrient for the brain) during periods of famine. The rise of ketones would replace glucose in other peripheral tissues in order to enhance the delivery of glucose to the brain. As blood-ketone concentration rises, the ketones displace the glucose and spares carbohydrate utilization for as long as possible. With this adaptation, it is easy to appreciate how important our own body preserves carbohydrates for the brain.

The brain optimally operates almost exclusively with glucose, a concept well accepted for decades. You may even experience this concept with temporary cognitive diminishment during episodes of extreme hunger. However, while this sensation would cease after a normal meal, meals devoid of carbohydrates fail to resolve the cognitive impairments and tends to leave keto-dieters in a type of “brain-fog” for an extended period of time.

Miraculously, as the production of ketones rise during ketosis, cognitive function can be restored from the metabolism of ketones in the brain. So, for all those who claim that ketosis makes them feel sharper and clearer, it’s not that ketones improve cognition as much as they simply restore the brain’s function from a state of starvation, the body’s natural defense to malnutrition.

The Bottom Line on The Keto Diet

The bottom line on the keto diet is that it can be very effective for weight loss and fat loss, but evidently not significantly more effective than any other diet of nutritious foods, maintaining the same calorie deficit. The miracle-like claims of being in a ketosis state seem largely overstated and unsupported by research and in fact appears to even impair physical performance and training adaptations.

Given the available evidence, based on the impact on the functions of the body, it appears the keto diet may be a lot more hype than help after-all. We aren’t quite finished discussing everything regarding “keto” just yet though. Next week, we’re going to dive into supplemental, exogenous ketones and examine their role, claims and overall impact according to all the research and scientific data currently available. Could supplementing with ketones be a true biohacking shortcut? Could added ketones be the bridge, filling the gap of traditional keto dieting pitfalls? Check back in at the RadLab next week to find out everything you need to know about ketones.


  1. Burke LM, Ross ML, Garvican-Lewis LA, Welvaert M, Heikura IA, Forbes SG, Mirtschin JG, Cato LE, Strobel N, Sharma AP, Hawley JA. Low carbohydrates, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. 595; 2785-2807, 2017.
  2. Cox PJ, Kirk T, Ashmore T, Willerton K, Evans R, Smith A, Murray A, Stubbs B, West J, McLure SW, King MT, Dodd MS, Holloway C, Neubauer S, Drawer S, Veech RL, Griffin JL, Clarke K. Nutritional ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metabolism. 24; 1-13, 2016.
  3. Hallbook T, Ji S, Maudsley S, Martin B. The effects of the ketogenic diet on behavior and cognition. Epilepsy Res. 100; 304-309, 2012.
    Yancy WS, Olsen MK, Guyton JR, Bakst RP, Westman EC. A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet To Treat Obesity and Hyperlipidemia. Ann Intern Med. 140; 769-777, 2004.