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The Keto Diet

Donate It's the latest fad diet, and people are trying it for just about any benefit you can think of.  

by Brian Dunning

Filed under Fads, Health

Skeptoid Podcast #664
February 26, 2019
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The Keto Diet

So long as diet gurus create websites and publish books, there will alway be grist for the mill keeping Skeptoid supplied with fad diets to discuss. They come and go, and always have and always will: the paleo diet, the low-inflammation diet, the Atkins diet, the blood type diet, the gluten free diet, the GMO free diet, and so on; and the one we're all bombarded with today is the keto diet. It's claimed not only to produce weight loss but also to provide a range of other surprising health benefits, which sounds like the familiar trope accompanying most fad diets. However, some evidence suggests that there's some truth behind at least a few of the claims made by the keto diet. Today we're going to sink our teeth into this fatty subject, and separate the fact from the fiction.

First of all, we'll cover the simplified version of what the keto diet is. The rule is to cut out all the carbs: bread, beer, fruit, pasta, potatoes — and load up instead on protein and fat: meat, cheese, butter, oil, eggs. The idea is to put your body into a state called ketosis. Our bodies require a certain amount of glucose as our fuel, and normally we get this from the carbohydrates in our diet, as that's the most bioavailable source. But if we cut carbs out of our diet, the body needs to get its fuel elsewhere, and fortunately it has other resources. The first one is to break down amino acids: proteins — basically our muscles — to get that glucose. So people on the keto diet try to eat plenty of protein to prevent their muscles being consumed. The second source is fat, which is why we have fat. But for the body to do this, it has to make some changes, and that's the state called ketosis. Your blood transports fat to your liver where it gets converted into chemicals called ketone bodies, and your cells can use these as an alternate fuel source. You may have seen urine test strips people can use to detect this change in blood chemistry, and these strips are indeed an easy way to verify you've put your body into ketosis. If you have, congratulations, you are now burning away your fat.

If this sounds familiar, it is. It's the basic idea behind the Atkins diet, the South Beach diet, all the various low-carb diets that were all the rage in the 1990s and early 2000s. They do work for weight loss. They work as long as you choose to keep them up.

However, there is an enormous proviso to make here. We have many decades of study data from every type of diet imaginable. That data is very clear that the makeup of your diet — whether it's low carb, low fat, or anything else — makes no difference to weight loss. The only thing that matters over the long term is that you reduce your caloric intake.

You probably know the diet advice I always give: Humans are omnivores. We can, and do, get along just fine on just about any diet imaginable around the world. It makes little difference what your calories consist of. If you're listening to this podcast right now, you probably live in some reasonably industrialized country, and malnutrition is not a problem you're likely to face — with very few exceptions, we all get more than enough of the nutrients our bodies need each day. We talked about this in Skeptoid #216, The Things We Eat. You need amino acids, fatty acids, vitamins, minerals, and water. You don't need carbohydrates, but they are the main thing your body's looking for as its favorite fuel source. If you eat anything close to a normal meal, you get more than enough of all of these. We even talked about one surprising solution in Skeptoid #629, Three Big Macs a Day. If your diet consists of three Big Mac hamburgers a day, plus some water, you're getting much more nutrition than you need, and far fewer calories than most people need — so it would be an effective weight loss diet. And whereas this diet slightly exceeds the recommended maximums of fat and sodium, it exceeds them by much less than does the average American diet. And where it doesn't quite meet some of the vitamin recommendations, a single five-cent Flintstones vitamin pill more than makes up the difference. The value in pointing this out is to drive home the point that any half-reasonable diet is perfectly healthy, so long as you don't eat too many calories. The Maasai lived on a diet of blood and milk loaded with cholesterol, and the Inuit lived on a diet of blubber that's nearly all saturated fat... and none had any endemic diet-related problems.

In other episodes, we've spoken about how proponents of perpetual motion machines will never be able to overcome the laws of thermodynamics. Here, by the same token, neither will fad diet gurus. It is simply not possible for a person to lose weight unless the calories in / calories out balance changes. And it's this fundamental law of nature that is the primary reason most fad diets do result in weight loss, so long as they are adhered to. Any kind of a restrictive diet — in which some foods should be avoided — results in fewer food choices, and inevitably, less total food consumed. Calories in drops below calories out, and we lose weight. You could create an all-bananas diet or an all-hamburger diet; as long as you're eating fewer calories than your body burns, nothing else about your diet matters. You'll lose weight, and getting closer to your body's ideal weight is one of the best things you can do for it, with myriad health benefits.

And this is the primary reason why the keto diet — so long as it is adhered to — does result in weight loss.

The keto diet encourages you to eat lots of fat as well as lots of protein. This raises a question: Why eat the fat? If we're getting the body into a state where it's burning fat, wouldn't we rather have it burning away that spare tire, rather than giving it a new source? The answer is that not everyone on the keto diet is trying to lose weight. It is often chosen by those who are in pursuit of other health benefits.

The history of the keto diet, in fact, is rooted in the treatment of disease, not in dieting or wellness. Since the days of the ancient Greeks, it's been observed that fasting reduces the frequency of epileptic seizures. Only in the 20th century was a working theory formed, which was that fasting puts the body into ketosis, and this change in chemistry is what was responsible for the reduction in seizures. The keto diet today remains a standard treatment for childhood epilepsy.

This resulted in something of a live, working laboratory for what other things ketosis might be able to do in the body. So far, it appears that it's useful for diabetics. Some people with Type 2 diabetes are able to get completely off their medication by sticking to a keto diet, and there is some evidence that Type 1 diabetes sufferers may also benefit, though to a lesser degree.

There is also theory suggesting that ketosis might be helpful in treating a variety of neurological diseases, including Alzheimer's, Parkinson's, and ALS; even migraines, sleep disorders, and bipolar disorders. So far the only supporting evidence for these have been pilot studies with limited data sets and results that are either inconclusive or encouraging, but it is an interesting area of research. The brain can indeed run on this alternate fuel source, and the plausibility for neurological change with this different biochemistry at play is real.

But the potential for improved function in some people with impairments such as Alzheimer's has led some to take a leap of logic and wonder if a keto diet can also confer improved function to people without impairments — basically, a smart pill. Make your brain work faster, remember better. However, there's no reason to think keto can improve the function of a healthy brain. Working around an impairment is not the same thing as creating improvement where no impairment exists.

Some people are actively touting ketosis to treat cancer, on the not-implausible principle that cancer cells require more glucose than regular cells, and so would be more adversely affected than regular cells by the removal of that fuel source. While this is good-enough theory to justify further study, it is by no means confirmed experimentally, and anyone who has cancer should absolutely not put their conventional treatment on hold in order to try a keto diet. Theoretically, there doesn't appear to be any risk in trying the keto diet supplementarily, but anyone undergoing cancer therapy should only try anything under the guidance of their oncologist.

There is also a growing movement of people who switch to the keto diet in the hope of improving athletic performance. The body stores fat a lot better than it stores carbs, so some endurance athletes reason that if you can fuel your body with ketones, you're not going to run out of energy nearly as quickly.

This has been tested a number of times, but with consistently disappointing results. Athletes always fare worse when trying to perform using ketones as a fuel source. Supplement companies, seeing an opportunity, have responded with ketone supplement products that claim to jump-start your body into ketosis. One such study published in 2017 in Frontiers in Physiology gave ketone supplements to elite bicycle racers to test their performance on instrumented cycling ergometers to simulate an actual race. All participating athletes thought they did better because they felt they were pedaling harder; in fact, all did significantly worse. And this was just one study among many done so far. What we know at this point is that the keto diet harms athletic ability.

Not only that, it has side effects. Most people, while their bodies are adjusting to ketosis, experience what's come to be called "keto flu". You feel weak and develop symptoms that resemble food poisoning, a condition that sometimes lasts for weeks or even months. Ketones in the lungs produce a foul halitosis called "keto breath". Constipation is also a common effect.

And so, the bottom line? If you happen to be one of the small percentage of people with either epilepsy or diabetes and are using a keto diet to help control it, then you're probably under a doctor's care and didn't need this episode. If you're one of those looking to get some other health benefit besides weight loss — well, it's unlikely you're going to get what you're after, but the risk of trying it is minimal. If you want to try it as an alternative treatment for something like migraines, you can, but the chances are minimal that the benefits will outweigh the inconvenience of the side effects. However, if you're using the keto diet to lose weight, then stick to it, and you'll likely be successful — but no more or less successful than if you chose any other dieting method to reduce your caloric intake by a similar amount. Because, as we say: You're an omnivore. Where you get your calories just doesn't matter all that much.

By Brian Dunning

Please contact us with any corrections or feedback.


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Cite this article:
Dunning, B. "The Keto Diet." Skeptoid Podcast. Skeptoid Media, 26 Feb 2019. Web. 19 Jun 2024. <>


References & Further Reading

Balasse, E. "Kinetics of ketone body metabolism in fasting humans." Metabolism. 1 Jan. 1979, Volume 28, Number 1: 41-50.

Cox, P., Kirk, T., Ashmore, T., Willerton, K., Evans, R., Smith, A., Murray, A., Stubbs, B., West, J., McLure, S., King, M., Dodd, M., Holloway, C., Neubauer, S., Drawer, S., Veech, R., Griffin, J., Clarke, K. "Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes." Cell Metabolism. 27 Jul. 2016, Volume 24, Number 2: 256-268.

Fan, S. "The fat-fueled brain: unnatural or advantageous?" Scientific American. Nature America, Inc., 1 Oct. 2013. Web. 19 Feb. 2019. <>

Freeman, J., Kossoff, E., Freeman, J., Kelly, M. The Ketogenic Diet: A Treatment for Children and Others with Epilepsy. New York: Demos, 2007.

Leckey, J., Ross, M., Quod, M., Hawley, J., Burke, L. "Ketone Diester Ingestion Impairs Time-Trial Performance in Professional Cyclists." Frontiers in Physiology. 23 Oct. 2017, Volume 8, Number 806.

Novella, S. "Keto Diet for Neurological Disorders." Science Based Medicine. New England Skeptical Society, 20 Feb. 2019. Web. 20 Feb. 2019. <>

Reynolds, G. "Can Ketones Rev Up Our Workouts?" The New York Times. The New York Times Company, 8 Nov. 2017. Web. 19 Feb. 2019. <>

Schwarcz, J. "Keto diet can help with epilepsy, Type 2 diabetes." The Right Chemistry. The Montreal Gazette, 15 Feb. 2019. Web. 19 Feb. 2019. <>


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