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  • Welcome to ZOE science and nutrition, where world-leading scientists, explain how their

  • research can improve your health.

  • Ketogenic diets ignite furious debate.

  • Keto has been promoted as a magic bullet for weight loss by its supporters.

  • And slammed as dangerous by its opponents.

  • It's no surprise, that completely removing almost all carbohydrates is not what most

  • people consider a balanced diet.

  • With carbs off the table, and on keto, we still need to find our energy somewhere.

  • This means a dramatic increase in fat intake.

  • At the same time drastically reducing carbs means starving our gut microbes of the fiber

  • that feeds them.

  • Nonetheless, doctors prescribe keto diets to treat people with severe diabetes and see

  • dramatic improvements and many healthy people swear by keto for weight loss.

  • On top of this removing carbohydrates prevents blood sugar spikes and crashes, linked to

  • inflammation and disease.

  • On today's show, we want to ask what the latest science says.

  • Are keto diets a crazy fad or could keto be right for me?

  • To help answer this question, I am joined by a leading nutritional researcher, Christopher

  • Gardner, a professor at Stanford University and a member of ZOE's scientific advisory

  • board.

  • Christopher is excited to share the results of his landmark clinical trial of keto diets

  • published this week in the American Journal of clinical nutrition.

  • You'll find links to this paper in our show notes.

  • Christopher, it's always such a pleasure to spend time with you.

  • And I'd like to start with our regular quick-fire round of questionnaires that our listeners

  • are sort of used to now.

  • So let's kick off.

  • Can you improve your health on a ketogenic diet?

  • That's complicated because there are good and bad ketogenic diets and there are good

  • and bad normal diets.

  • I can imagine a ketogenic diet that's healthier than some people's regular diet if you followed

  • it a certain way.

  • So we'll have to come back to that.

  • All right, so it's complicated.

  • Can you lose weight on a keto diet?

  • Absolutely.

  • It's a very restrictive diet.

  • For the things that are still allowed, the palatability will run out quickly and you'll

  • say, I am hungry, but not for that.

  • So nope.

  • Not gonna eat.

  • Lowered my calories.

  • Lost weight.

  • Is keto a good diet for most people?

  • I'm personally opposed to it because of its absence of grains and fruits and beans, which

  • don't seem justified to me.

  • So I don't think in the long run that it is, it's great for getting rid of added sugar

  • and refined grains.

  • Is doing keto from time to time helpful?

  • I'm opposed to anything that isn't a diet pattern that you'll follow for life.

  • I'm opposed to things that are just transient, I'm gonna do this for a while and it's a diet

  • that I'm going on, and then I will go off the diet when I got where I wanted to be.

  • Well, if you go off it, then the other stuff comes back and it was useless.

  • What's the biggest misconception about the ketogenic diet?

  • That it's high meat.

  • People think it's low carb.

  • And what has low carbs?

  • Oh, well, meats have low carbs, but really the ketogenic diet is a high-fat diet.

  • If you end up eating a lot of protein, then you've met your needs for the day and you

  • convert your proteins into carbs and fats, and whoop.

  • You threw yourself outta ketosis by making carbs outta your protein.

  • That's amazing.

  • And I did not know that.

  • Thank you, Chris.

  • The final question will cutting out carbs.

  • Stop your body's ability to process them?

  • No.

  • That was simple.

  • All right.

  • Well, look, I'm really looking forward to digging into those answers more, the whole

  • topic of ketogenic diets ignites furious discussion.

  • And I think a lot of confusion, I personally have never tried it because of the idea of

  • giving up bread and croissant for good, I just know that's a step too far, but as someone

  • with bad blood sugar control, I know there's some impressive evidence that keto can help

  • people with diabetes come off insulin.

  • So there's some real clinical evidence that suggests there's something interesting there.

  • And so I think it really fascinating, Christopher, for you to take us through this, and maybe

  • we could just start with what is a ketogenic diet and how does it work?

  • Sure.

  • So the ketogenic diet actually goes back 50 years as a diet that was used to treat epileptic

  • seizures.

  • It's been around for a really, really long time, but it's really odd that people are

  • now taking this and doing it for weight loss and some athletes are trying it.

  • And it's certainly relevant in the world of overweight obesity, and diabetes, because

  • a lot of that has to do with excessive carbohydrate intake and the inability to process those

  • carbs.

  • So if you wipe carbs outta your diet, if you go to extremely low levels, other than some

  • above-ground vegetables, and maybe some berries, you can resolve some insulin resistance issues,

  • and you will lose some weight.

  • So there is some basis of interest in this, especially given how many simple and unhealthy

  • carbs people eat these days, but a central component of our discussion, Jonathan should

  • be good carbs versus bad carbs.

  • Brilliant.

  • And before we go on to that, because you mentioned the word ketosis before.

  • Can you explain a little bit more beyond just this idea that I'm not eating carbs and I'm

  • eating fat?

  • What is this ketosis, what is going on inside my body as a result of following this diet?

  • If you think about this, the normal person on an average day is gonna burn a combination

  • of carbohydrates and fats all day long.

  • I think everybody, at least in the US learns this phrase.

  • The mitochondria are the powerhouse of the cell.

  • That is the basis of biology in the US.

  • I think my son told me he learned that this month.

  • So there you go.

  • I think it's universal.

  • I think it's universal.

  • And it has to do with the thing called the Kreb cycle or the TCA cycle is another name

  • for it.

  • So you've lost me now.

  • So, so explain.

  • It's a cycle where carbs feed in at one end and fats feed in at the other end.

  • Carbohydrates are usually 5 or 6 carbon atoms bound together.

  • And fats are anywhere from 4 to 26.

  • And you feed in as fats break down little 2 car units and you feed in as glucose breaks

  • down little 3 and 4 car units, and you spit out carbon dioxide.

  • You breathe in oxygen and as you breathe in oxygen, you breathe out CO2.

  • What happened?

  • Ugh.

  • You added carbon to the oxygen.

  • You just breathe in.

  • And in doing that every time you break carbon bonds, you make energy.

  • So glucose and fat all day long is what people burn.

  • If you stop eating carbohydrates to a very low, low, low level, then this cycle stops

  • running.

  • And these little two carb units of fats that are breaking down to provide you the energy

  • that usually gets burned together with carbs, start to pool up, and they have an alternate

  • path.

  • They make ketones.

  • They make four carbon units and these four carbon units can be broken down into single

  • carbs and can generate energy.

  • But it's in a slightly different pathway that excludes the use of carbohydrates.

  • And a lot of people probably do this actually overnight.

  • If you haven't eaten for 6, 8, 10, or 12 hours, some of your carbohydrate stores are used

  • up.

  • And so overnight, most people probably make some ketones.

  • Over the course of teaching nutrition, we say, you know, really is healthiest to have

  • carbs and fats burning together.

  • There's a blood-brain barrier.

  • The blood-brain barrier in the central nervous system doesn't like to burn fats.

  • They really prefer, and almost exclusively can only use glucose because that's what will

  • get into the cells.

  • But in the absence of glucose, if you had to these four carbon units that are ketones

  • could feed the brain and they could feed the central nervous system.

  • So now there's this movement, oh my God, maybe it's even better.

  • The keto folks are saying, oh God, maybe ketones are even better than glucose feeding the brain

  • feeding the central nervous system.

  • And that was sort of a pivot point in trying to think, could you just burn fat instead

  • of burning carbohydrate and fat together, which is the usual recommendation.

  • Got it.

  • So it's an unusual situation to be in for our sort of normal historical diets to be

  • in this ketosis.

  • That is my strong opinion.

  • Got it.

  • So why have people become interested in this?

  • You mentioned that 50 years ago, they looked at this for epilepsy.

  • That's a long time.

  • Why the discussion today?

  • Sure.

  • I would just speculate that it's part of this ongoing whiplash about low-fat diets, not

  • being the best thing for us.

  • And so maybe it should be low carb.

  • Maybe it should be lower carb.

  • Oh my God, maybe it should be extremely low carb.

  • When you use the terms low, fat, and low carb, you need a qualifier to go with that.

  • Is low, lower than yesterday?

  • Is low half as much as you had before?

  • Is low 75% or 25% of what you had, but it's quite undefined.

  • What do low carb and low fat mean?

  • And so Jonathan, when we go to the literature and I'm trying to pool studies together and

  • say, oh, let me summarize all the low fat, low carb studies.

  • Oh my gosh.