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What Is The Ketogenic Diet Really About? A Q&A Session With Lyle McDonald

Lyle McDonald

By Lye McDonald

After becoming involved in cycling, triathlon, weight training and gymnastics in high school, Lyle McDonald went to UCLA to study exercise physiology.  During that time he became interested in all aspects of human performance including… Read more.

If you’re serious about bodybuilding and your nutrition, chances are you’ve heard of Lyle McDonald.

If, however, you’ve been living under a rock in a weight lifting bubble and are unaware of Lyle, then all you really need to know is that he is one of the world’s leading authorities on sports nutrition, specifically the idea of low-carb dieting.

The Ketogenic Diet Myths and Truths Header with Lyle McDonald

Controversial yet widely respected, Lyle has spent the past 2 decades of his life studying human physiology and researching the science and practice of human performance, body recomposition, muscle gain and fat loss.

In fact, a few years ago, Lyle underwent a personal journey of scientific discovery by conducting an experiment on himself based on Dan Ducaine’s Body Opus programme. As a result of his experiences, Lyle went onto to write The Ketogenic Diet.

This book is just one of many that Lyle has written cementing his status as a world leading sports nutrition expert.

So when we bagged one hour with him, we thought it only fair we gave YOU the opportunity to ask him your burning questions… Well, we are good to you like that!

Out of the 100s we received, we whittled them down to just 5…

Is it true that you "can't out train a bad diet" or is this a corporate sports nutrition scare tactic?

(Josh Logan, 21, Manchester)

Unless you are an elite athlete capable of doing 6-8 hours of training per day and your daily energy expenditure is 6000+ calories per day (and you spend 8 hours training and 8 hours sleeping so you have limited time to eat), you can't do it.

Just do the math.

Can you train out a bad diet?

An hour of hard aerobics burns maybe 600 calories per workout.  A bagel has about 300 calories.  One donut has 250 calories.  Eat 3 of either, and that's a mildly bad diet, and you've easily out eaten your training load.  Even if you're a beast and go 900 calories/hour (and let's face it, what person that has a bad diet does that much work), it's still 4 donuts worth. 

A bad diet wins every time.

The caveman diet (Paleo) is extremely popular, do you see any merit to this type of diet?

(Kiera Mcfall, 28, Glasgow)

In the sense that more people would benefit from putting less pie in the piehole, sure.  But how is this new?

Every nutritionist/sports nutritionist in the history of ever has recommended people eat less refined high-sugar/high-fat crap.  Paleo just makes it into a cult/religion.

The Paleo Foods Pyramid

But then they go too far. They conveniently cherry pick not only what research they choose to believe (i.e.  recent work suggests that 'paleo man' ate grains but since the paleo cultists think grains are evil, they say it's a false finding). 

And of course if they are going to argue that “Paleoman didn't eat X” then they should realize that Paleoman didn't blog on their iPad while wearing Vibram 5 fingers and going to a commercial gym while consuming antibiotics as needed, driving in their car and living on a centrally heated and air conditioned house while prattling on Facebook about how they are better than everybody else.

Neither did Paleoman have Whole Foods or other expensive health food stores to buy grass fed beef at.  The paleo folks pick the one easiest thing to follow and then get really self-righteous about their superior lifestyle.  If there are health benefits to the paleo lifestyle it's to the lifestyle which is more than just the diet.

Daily activity, a lack of stress, a lot of other factors go into this.  But those are difficult and shopping at expensive health food stores is easy.  But it's just one big cherry pick.

In the UK recently there has been a media storm surrounding the supposed "breakthrough" that low fat diets are better for you than low carb diets (very reminiscent of the 80's trend...) for weight loss what would your response to this be?

(Chris Whitting, 25, London)

I did a very full analysis of this study on my website.  And while it's an interesting finding, the results should be taken with an understanding of its limitations.  It was only 6 days long for example and there are longer term adaptations that can occur in fuel use with longer time periods.  Nobody diets for 6 days either.

For example, the obese are known to lose metabolic flexibility (their muscles do a poor job switching from glucose to fat for fuel).  If you glycogen deplete them with hard exercise, they adapt to a higher fat diet more quickly.  Of course, it's arguably true that the obese don't do a lot of hard exercise.

Bread, Milk, Cheese

Since nobody diets for 6 days, I'm just not sure that's relevant.  Perhaps of more importance is that the low-fat diet was an 8% fat diet containing 17 grams of fat.  The researchers did this for a very clear reason but that's not a realistic diet in the long-term. 

At the end of the day, adherence trumps everything else.  Small differences in fat loss notwithstanding, nobody but the most psychotically driven athlete is sticking with an 8% fat diet for very long.  So who cares what happens over 6 days?

The best diet for a given person is the one that the person can stick to in the long-term.  At least one study shows that moderate fat diets (about 30%) show better adherence for example.

Which is better, "clean eating" or "if it fits your macros"?

(Lauren Kerr, 23, Leicester)

It's a dumb question.  It's a false dichotomy that comes out of a gross misunderstanding of IIFYM which is due, unfortunately, to a handful of vocal idiots online, who make it sound like IIFYM is the Poptart or Junk Food diet.


If you look at the way that the grand majority of people who use IIFYM eat, it's easily 80-90% clean (whatever in the hell that actually means since clean has no objective meaning) but with the occasionally included treat.

It may not even be every day but if that person has a craving for something a couple of times per week and it fits their macros, they eat it.  That's IIFYM in a nutshell.  Mostly clean eating but you can include a treat if you want or need it.

And the research shows without exception that flexible eating patterns are superior to rigid habits with clean being one of the most rigid habits out there.  What's funny is that when clean eaters go off the rails and binge, or deliberately include a full cheat day, they easily end up eating far MORE crap foods than the average IIFYM'er.  While maintaining that clean eating is superior.

So I consider it a non-question in the first place.

Critics say the Keto diet is more than just an unhealthy way to lose weight - it is outright dangerous - first of all, what would your response be to this.  Secondly, could you explain what the Keto diet is and how people can, should they wish to, follow it safely?

(Phil Clark, 33, Cambridge)

Most if the ideas that a ketogenic diet is dangerous comes out of a gross misunderstanding.  There is something that occurs in Type 1 diabetics, who produce no insulin, called runaway ketoacidosis.  Ketones are kind of broken fats produced in the liver when insulin is low and another hormone called glucagon is high. 

A Type 1 diabetic produces zero insulin and they can start producing some many ketones that they become acidotic.  Their fat cells are dumping fatty acids into the bloodstream at an unchecked rate (even low levels of insulin inhibit fatty acid release by 50%.  Ketone production in the liver goes up and up and up.  The real cause of death here is actually dehydration.

But this never happens in non-Type I diabetics.  Never.  There are three different feedback loops in the human body that prevent it.  Not the least of which is that high ketone concentrations stimulate insulin release.  This not only inhibits fatty acid release but shuts off ketone production in the liver.  Ketone concentrations will never go as high as is seen in ketoacidosis.  Never.  It can't become a runaway situation because the non-Type 1 diabetic can still make insulin.

As to unhealthy, that's kind of a difficult question without knowing what is being claimed.  Studies have clearly shown that in the person with metabolic syndrome (referring to a cluster of factors insulin resistance and others); ketogenic diets improve a variety of health parameters even if weight isn't lost.  It's not even debatable here.

x marks the food

I imagine that some would take issue with the "high-protein" nature of the diet but that comes out of other misunderstandings with every study on the topic showing that a higher protein intake while dieting is superior.  It blunts hunger, stabilises blood glucose and helps with long-term weight maintenance.

It's often thought the vegetable intake on a ketogenic diet is very low and this can be partially true.  Certainly total carbohydrate intake is low (below 50-100 grams per day) but my experience is that when people can only eat small amounts of carbohydrates, they eat MORE vegetables than on a carb-based diet.  When you can eat lots of starches, you eat those.  When you can't, you eat more vegetables.

The high-fat nature could potentially be an issue but a lot of that depends on food choices and what fats are being consumed.  There has recently been some interest in a Mediterranean ketogenic diet, with more vegetables and a focus on the relatively health neutral monounsaturated fats (found in Olive oil for example).

So long as weight/fat is lost, invariably blood lipid levels improve on a ketogenic diet.  If weight/fat isn't lost, they can get worse but it depends on the fat intake.  Again, primarily in the person with metabolic syndrome, ketogenic diets drastically lower blood triglyceride levels (which higher carbohydrate diets can increase depending on the carbohydrate source).  And blood TG levels are an independent risk factor for heart disease.

Given the recent interest in the gut microbiota, there is limited (one study I'm aware of) research showing that a ketogenic diet might negatively impact on the gut.  But more research needs to be done and so long as sufficient fibrous vegetables (which are pre-biotics, improving the gut health during fermentation to short-chain fatty acids) are being consumed, this is probably secondary.  It would have to be weighed against the other potential benefits.

There is also, as I recall, some concern over long-term bone health but don't swear me to that.  Keto diets can cause some dehydration and mineral loss but this is easily remedied with supplementation of sodium, potassium, magnesium and calcium.

Finally there is a mistaken idea that the brain can only use glucose.  But this is untrue.  While the brain can't use fatty acids directly, it can use ketones, made from fatty acids.  They actually exist to fuel the brain during total starvation which is what a ketogenic diet mimics.  But it does take a few weeks for the shift to occur and some people feel pretty bad during that adaptation period.

Foods with Fatty Acids

Sufficient minerals help with this and some short-term studies have found a decrease in some types of mental performance but this is a time thing.  A one week study doesn't tell you anything about long-term dieting (any more than the 6 days study tells you what happens in the longer term).

At the end of the day, like most things, ketogenic diets have pros and cons.  Most of the idea that it is dangerous is completely unfounded, a complete misunderstanding.  Health wise, it has pros and some potentially unknown cons.  If there is any true criticism here it's that we simply don't know the long-term effects.

The ketogenic diet is used clinically to treat epileptic children and is showing some promise in other neurological disorders not the least of which is treating a very specific type of brain cancer in the glioma (note, despite idiocy on the Internet, ketogenic diets have not been shown to “cure” cancer).

These children they are typically kept on the diet about 3 years with no negative signs.  Not that this is a perfect comparison by any means, but if any dangers or health problems were showing up in that time frame, they would have.  And they simply don't.  What might happen beyond that is anybody's guess.

Gutted your question didn’t feature?  Don’t worry – this is going to become a regular thing so if there is anything you’d like Lyle or one of our other guest authors just let us know on Facebook!

Lyle McDonald

About Lyle

After becoming involved in cycling, triathlon, weight training and gymnastics in high school, Lyle McDonald went to UCLA to study exercise physiology. During that time he became interested in all aspects of human performance including nutrition, training and supplementation. 

He would write his first book a comprehensive text on Low-Carbohydrate Ketogenic Diets in the late 90’s and has written 12 books on various aspects of nutrition, fat loss and training. He is currently finishing up a comprehensive book about women, training and fat loss. His work and books can all be found at or you can connect with him via Facebook.

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