This is what the Keto Diet does to your body

[Music] welcome to zoe science and nutrition where world leading scientists explain how their research can improve your health [Music] 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 completely removing almost all carbohydrates is not what most people consider a balanced diet with carbs off the table 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 are crazy fat or could keto be right for me to help answer this question i am joined by leading nutritional researcher christopher gardner a professor at stanford university 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 will 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 questioners that are that our listeners are sort of used to now um so let's kick off can you improve your health on a ketogenic diet that's complicated because there's good and bad ketogenic diets and there's 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 and for the things that are still allowed the palatability will run out quick and you'll say i am hungry but not for that so nope not going to 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 opposed to things that are just transient i'm going to 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 uh 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 out of ketosis by making carbs out of your protein that's amazing and i did not know that thank you chris 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 the idea of giving up bread and croissant for good i just know that's a step too far um 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 like clinical evidence to suggest there's something interesting there um and so i think really fascinating christopher 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 diabetes because a lot of that has to do with excessive carbohydrate intake and inability to process those carbs so if you wipe carbs out of your diet if you go to extremely low levels other than some above ground vegetables and maybe some berries you you can resolve some insulin resistance issues you will lose some weight and so there 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 this word ketosis before can you can you explain a little bit more uh beyond just this idea that i'm not eating carbs and i'm eating fat what is this ketosis like 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 going to burn a combination of carbohydrates and fats all day long i think everybody at least in the u.s learns this phrase the mitochondria is the powerhouse of the cell that's like the basis of biology in the u.s 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 krebs cycle or the tca cycle is another name for it and basically so you've lost me now so explain it's a cycle where carbs feed in at one end and fats feed in at the other end and carbohydrates are usually five or six carbon atoms bound together and fats are anywhere from 4 to 26 and you feed in as fats break down little two carb units and you feed in as glucose breaks down little three and four carb units and you spit out carbon dioxide you breathe in oxygen and as you breathe in oxygen you breathe out co2 what happened you added carbon to the oxygen you just breathed 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 carbohydrate 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 energy that usually get 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 to single carbs and can generate energy but it's in a slightly different pathway that excludes the use of carbohydrate and a lot of people probably do this actually overnight if you haven't eaten for six eight ten twelve 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 and the central nervous system don'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 and 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 sort of um for our sort of normal historical diets to be in this ketosis that is my strong opinion got it so um 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 why the discussion today and 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 and so i i think it's just been 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 percent of what you had but it's quite undefined what low carbon 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 they are all over the place and when a headline says low-fat yes low-carb no and the next day the other thing you have to say oh my god those are not really similar levels of carbs and fats they use completely different ones they use different sources of foods to achieve them so it's a gray area and i think keto has been a result of well could we go lower could we go lower could we go lower and there's some people who are fanatical about it and some people who are appalled many of them on on the west coast is i think definitely one of the hot spots uh of this right and so what you're saying is you know there was this whole thing about you know low fat being the way that we're all going to be healthier the evidence turned out to be really bad for this and so there's always been this just to make sure it's almost a swing back which is well in that case maybe carbs are the source of all evil could we go down to the point there's almost none how low so final question on this so if i want to be on a ketogenic diet i want to be in ketosis like how low carb is that what fraction of my diet is actually coming from from carbs so generally people start out at about 20 grams a day as a kickstarter point and then maybe go up to 50 grams a day now let me just tell you what that means with a little bit how many pieces of toast am i allowed with that christopher yeah so i mean most people have about 400 grams of carbs a day so there's not a lot it's not a lot of taste carbohydrates have four calories per gram that if you're eating 400 grams of carbs times four calories is 1600 calories and you're eating 3 000 calories a day that would be 50 carb so that wouldn't be 80 or 70 or 60.

and so let's say you're eating 300 grams of carbs that would be 1200 calories and if you're eating 2 000 calories a day that'll be 60 so we're talking quite if most people's diet is more than half carbs so to go to 20 to 50 grams means cutting back from three or 400 grams a day to 20 or 50 grams a day there's not many choices almost nothing there's almost no carbohydrate whatsoever is what you're saying this is extremely extreme i'm uh i'm not even allowed a single slice of bread i guess is what you're telling me not a chance no okay this is we've already established this is not the diet for me but that is fine that is not the purpose of this podcast let's um let's talk about your new study so it's just been published in the top journal american journal of clinical nutrition and we will provide links in in the show notes for anybody who would like to to read that um before we talk about the results of the study um i'd just like to take a minute to talk about the approach because you're really famous for doing large-scale randomized control trials and have done many and it's part of how we first got to meet um can you just explain why these sorts of studies are so important and why they are rare in nutrition sure yeah so first of all it's really hard to get people to change their diet it's much easier to get rats to change your diet you put them in a cage you only put that food in there and you're pretty sure they ate that and if they didn't you can see it the other thing we do is we say oh i've got 10 000 people and i asked them what they ate and i watched them over time to see what happened and i can select the people who ate the lowest of this or the highest of that and those are called observational epidemiological studies and the challenge there is that the people who did eat the most or the least of this or that tend to also do the most or least of other things like exercise or take supplements and it's very hard to pinpoint a causal relationship between diet and health outcome if they also did lots of other things that were different so the gold standard in theory and i don't want to provide some caveats for this is you randomly assigned them to diet a or diet b they had to agree to participate in one or the other willingly and so you do have people who exercise more or less you do have people who take more or less supplements you do have people of different weight and physical capacity but when you're randomized an equal number of both of those ended up in both groups and that's actually the way we control for those confounders is we say ah we balanced it it's in both groups so it's not different so that's the gold standard for us the challenge here jonathan is when you do a randomized control trial you really only get to pick one approach so in our randomized control trial which as you said is a great way to do a study from my perspective good design good to get it published good to find out information uh let's keep in mind that our one study is that it's one study got it so it doesn't answer all things it answers this very specific ketogenic diet it's very specific alternative diet and compares those two gives you these really strong scientific results but it doesn't tell you anything about a a third diet you're saying at this point i have no information on that yeah so i know some of the headlines are going to appear and say keto and mediterranean do this and do that and i'm just going to cringe and i'm going to say no if you really wanted to define the way we did it it would be too long a headline and no one would read it and it wouldn't be good clickbait but that's really how it works well so the good news is this is a podcast we got a bit longer christopher so maybe just tell us about the study um what what were you actually doing and then tell us what the results were yeah i i took a very specific approach to this i think it's really been fascinating this whiplash from low fat to low carb back and forth and i tend to see the two compared head to head and ketogenic is definitely a low carb diet so you would think maybe somebody would want to compare that to a low fat diet but my interest is actually in grades of low carb i mean a really fascinating thing about the yummy tasty mediterranean diet is it exceeded what was for a long time in the u.s a cutoff of 30 total fat don't have any more than that if you do that you end up with a lot of carbs and so if the mediterranean diet ends up being 35 40 45 or 50 fat and you get 20 percent of calories from protein you now have a low carb diet but not 5 or 10 calories 30 35 or 40 percent got it so in comparison to what you're talking about like to be ketogenic you've got to have this incredibly low level of carbohydrates you could still have what a normal person might think of as a relatively high fat diet maybe compared to what they were taught when they were younger i was i always talk about like my dad being told he had to go on this very low fat diet because he had high cholesterol you know sort of 50 years ago so for him like what still seems like a radically high fat diet because it's got olive oil and nuts or whatever but you're saying so radically different from the other the the ketogenic diet that you were you were testing yeah and so our idea here was that we would make a mediterranean and a ketogenic diet that were designed in such a way that they agreed on three things lots of ground vegetables and i'll just clarify the reason i'm saying that is that avoids potatoes and tubers and carrots so the ketogenic diet focuses on broccoli and cauliflower and red bell peppers and things like that that are above ground because the below ground vegetables tend to be starchier and the absence of added sugar and refined grains so those are three components it's similar and then beyond that the ketogenic diet says oh my god to get down to 20 or 50 grams of carb a day you can't have any grains even whole grains you can't have any fruits other than occasional berries that's the one allowance they give you you can't have any beans no chickpeas no lentils no pinto beans kidney beans things like that which is quite odd because if you go to the dietary guidelines for americans or the world health organization or the american heart they will say please try to increase your whole grain intake your fruit intake and your legume intake legume covering the whole thing of lentils chickpeas peanuts beans things like that and your issues that these are high these high fiber foods also inevitably have carbohydrate in them so you just can't eat them and stay within this very very tight um daily limit and being the microbiome lover that you are jonathan and i know you are a recent convert to the microbiome uh if we're going to feed the microbiome with fiber the main sources are going to be whole grains and beans and fruits and yes vegetables but i don't think you can get all that much fiber from vegetables so yes all those fiber rich sources are also high in dietary carbohydrates so if you wanted to get to 20 to 50 grams of carbs a day you'd have to wipe out those entire food groups which would run counter to pretty much every public health recommendation that's out there and so jonathan i want to be very specific about how we frame this question we want to design our specific diets we're calling it the keto med study but it's really a well-formulated ketogenic diet according to finney and volit reading that book and it's also a mediterranean plus diet if you go to lots of different mediterranean scores they'll tell you the things to eat the most of in the least of and none of those scores have i ever seen avoid added sugar and refined grain i don't think it's counter to the mediterranean diet but i don't see it in the scores where they try to see how mediterranean you are so we called it the mediterranean plus diet and i think you know for our listeners who um you know if you're not in you if you're in nutrition people talk about mediterranean diet all the time but i think you're outside of uh nutrition particularly maybe if you're living in europe somewhere then you're a bit confused because like there's a lot of countries and i've been to spain and i've been to france and italy and greece and they seem to eat really different things so there's a sort of concept of a mediterranean diet right christopher which is more like a label um to be applied to i guess a view of what is healthy what are the core you know what is a mediterranean diet you know when when you describe this because i think everybody every nutritionist i ask would give me a different answer so it's funny because i'm actually working on a write-up of this right now and i've got a whole bunch of mediterranean studies where it said this is what we call mediterranean and it's basically more vegetables more whole grains more beans more fruits uh fatty fish avocados olive oil it's actually less meat i've seen them flip-flop on dairy actually yolk greek yogurt seems very mediterranean some of the scores want to do an absence of yogurt quite a few of them say less meat some of them say switch red meat for poultry and fish most of them say fish is mediterranean so those would be the major categories alcohol is a really odd one alcohol in all the mediterranean diet scores hopefully this will sound mediterranean to your listeners you get dinged for not drinking and you get dinged for excessive drinking and you get a point for drinking moderately all right that uh that sounds like most of my mediterranean uh experiences so uh that seems good seems real so and i guess one of the things out of that then that if you uh that's in common is in all those cases you're saying not sort of the highly processed foods that are such a big part of um of our diet you know even with all those variations that sounds you know that's sort of one of the the big thing that seems like it's in in common and very different from from what most of us are eating yeah and i think if we stepped back and took it at that level the greeks and the turks and the french and the moroccans would say well yeah yeah yeah you're right so the question was centered around the keto diet having this complete absence as much as possible of whole grains and fruits and beans so three things similar and three things different than so the way the question is frame jonathan is if we take people with type 2 diabetes or pre-diabetes and we ask them to go on these two diets for 12 weeks each in a crossover manner so everybody gets to try both of them we are assuming since they both eliminate carbs in terms of added sugars and refined grains that they will experience blood glucose benefits but would there be an additional benefit by getting rid of the whole grains and the fruits and the beans that that would seem counter to health professionals advice so we were looking to see if there was an additional benefit so so what what what happened you've been teasing us and now we want to know i i hear quite a lot of skepticism about the ketogenic diet so i'm assuming that it it was terrible what were the results no i so people lost weight on both diets uh we can get into some of the the pros and cons and there are some fun nuances to get into here so the main outcome in terms of olive glucose jonathan was glycosylated hemoglobin i don't know how much your listeners will know what that term is if you are a person with diabetes or pre-diabetes you would know this is something to do with uh the red blood cells in your body are sort of a 90-day marker of how well you've been managing your glucose so when you say glycosylated hemoglobin the hemoglobin's from your red blood cell and it means some glucoses molecules randomly stuck on the red blood cells and it sounded kind of a good hint then we looked at okay so what about other things that happen let's look at blood pressure let's look at blood lipids let's look at liver enzymes and pretty much across the board everybody did better in everything on both diets that the things that stuck out as being statistically significant were two one is that for the keto group their ldl cholesterol went up while in the mediterranean group it went down and that was statistically significant so that was a point for mediterranean in both groups their blood triglycerides went down but they went down even more drastically in the keto diet and so that was actually a point for keto and i think i think just to make sure we explain that for felicia's right that's that's really surprising because triglycerides is just like all the fats in your blood aren't they christopher so basically you're saying uh you ate nothing but fat pretty much is what you're saying and yet the fats in your blood went down uh is rather remarkable right it is and that's a really funny part of metabolism if you want me to go on a quick riff for that the idea there is that if you're eating fat it gets processed and stored as fat if you're eating a whole lot of carb the idea here is that you quickly absorb and use your carbohydrate for brain energy and muscles immediate needs the next thing you use it for is to replete these storage depots for glucose so some is in your liver some is in your skeletal muscle and it's pretty easy to fill up your stores and after that you turn all your carbs into fats so this is a bizarre concept jonathan but you got it right when you eat a high carbohydrate low fat diet your blood triglycerides go up but it's not because of the fat that you were eating that was being metabolized and put away in a more controlled fashion than the excessive simple carbohydrates that you're eating it's a very counter-intuitive finding you're correct and so the summary of your results if i understand rightly is that if you go on to this sort of um you know healthy ketogenic diet sort of the the best one that you've designed here actually the health results are really good you say all these markers uh have improved i've lost weight this sounds like a like a win christopher so it's a wash i would say it's a wash between the two they both worked for weight loss you get a point for one and a point against for the other but we looked beyond that so a couple of the key issues here are adherence and being able to maintain the diet and another factor given that our studies were our study periods were only 12 weeks long is what happens to other nutrient intake what might happen over years and years of doing this and what might happen to your microbiome because a ketogenic diet is pretty much by definition a lower fiber diet and i actually won't have these results to share with the listeners today but my colleagues justin and erica sonnenberg right now have a freezer full of poop from our folks and they are looking at what happened to the microbiome and we're looking at a whole panel of inflammatory markers so tell me if we're ready to look into the nutrient intake and even more interesting actually to start with would be the adherence if that's yeah let's talk about exactly that so adherence is like science word for sort of like how sustainable this is right like is there something that i can keep doing like i and here is when you tell me to do it but for myself it's like can i stick with this for the long term so um i mean for me that's always been the biggest concern about the the ketogenic uh diet as i think about you know friends and family members who have done this that they they've tried it for a bit and then it becomes very hard to maintain because you know you go to your kids birthday party and they're having a cake and there's a lot of societal pressure to eat a cake and i think you just explained that's already blown my my day but you've now done this real study like what have you seen in terms of sustainability yeah so and let's talk about there's an element of the design that i didn't explain for the 12 weeks jonathan and that is we decided that we wanted to kick-start everybody and get them to be as adherent or compliant following the directions as much as they could use whatever term you want and for four of the 12 weeks on each phase they had food delivered to them which sounds which sounds great i i haven't said all of this if you deliver the food to me i need almost anything and then by design we left the last eight weeks for them to prepare food on their own so that we could see how well they would you know what did it look like when they were very adherent and what did they look like in real life and we have one additional time point jonathan which is after doing the crossover and doing both diets in random order 12 weeks later we went back and asked him what they were eating because my big question was okay you definitely mastered this thing you had 12 weeks of help from a dietitian you had group classes you had individual meetings you had more help than most people will ever get when they try this on their own 12 weeks after the study what did you do so here's the fascinating thing is that on average we had made an adherence score from 0 to 10 and 10 was perfect and 0 was lousy we kind of assumed that when we delivered the food everybody would be at a nine or a ten both groups on average when we were feeding them food got a seven and a half out of ten so they didn't do a very good job but they went from you know a couple points before the study to seven and a half out of ten so that kind of looked pretty good okay interestingly more so on the keto diet than the mediterranean diet we had people scoring at the two three four level when we were delivering food some of them just outright rejecting the food that we delivered okay now first of all i i'm i'm irate but on the other hand thank you for being honest really you're we enrolled you in a study and you didn't do what we told you to do so is it is this does that undermine the finding or is that an important part of the finding that it was difficult to do fast forward now to when they do eight weeks on their own and when they did eight weeks on their own we again assessed how closely they were following the diet and interestingly on their own of the 40 or so people in the study five of them on their own kicked butt on keto they were all in the nine to ten range but about five of them were from zero to two and so it was very polarizing in my mind some people got it and some people just could not do it interestingly the mediterranean diet group had the same average level of adherence as the ketogenic group when they were on their own they were about a five and a half each when they had been provided all their food they were seven and a half each mediterranean group was yeah kind of from three to eight but interestingly no one when they were feeding themselves in mediterranean was a nine or a ten and i think that's partly because jonathan our mediterranean had a lot of rules you had to eat beans and whole grains and fruit and cut out added sugar and cut out refined grain and there are a couple other things like god i can't every day i got to keep track of all these rules the keto diet was more like don't eat carbs eat lots of fat it was a much shorter list of rules and so pretty funny to me that on average they look the same but if you look at the distribution across people some people did quite well at it and some people did not on keto that was different between the two groups and remember i said that we asked them 12 weeks when the study was over what were they eating yeah so what happened you had these people who got both and then 12 weeks later they had a real experience of both of these what were they doing yeah so the thing they all remembered the most was getting rid of added sugar in a fine grain they all did better than that this is at week 36 12 weeks of one diet 12 weeks of the other diet 12 weeks of nobody watching you anymore the studies all over they both did well at that they both maintained pretty much all the weight loss that they got in the first 24 weeks which is really fun to see but they pretty much went back to their old habits after that and when you scored that it ended up being a more mediterranean diet than a ketogenic diet so we saw that the keto diet was not sustainable even among those people who when they were getting their own food were scoring nines and tens for those eight weeks yeah they were gone they couldn't do it 12 weeks after the study was over so to me this is a hugely important part if the benefit that you get from the keto diet is being really low on carbs and seeing your triglycerides go down if if you can't maintain that then i'm not a fan and i think that's a really important question and i think this study that you've done like really takes us some way forward on this which is um how strictly do you have to follow the ketogenic diet in order to be worth it we had lots of listers questions really on this because many many of our listeners have tried this and many of them are therefore not fully on it like in your view how strictly keto do you need to be in order to get the sort of health benefits that you saw in the the ketogenic part of this study yeah well in theory you have to be in ketosis and so another thing we did jonathan that i haven't mentioned is we looked at blood levels of ketones and most of them were not in ketosis they couldn't do it they might have some of more of them did it during the feeding phase of this study they were most successful there almost no one was able to do it when they were providing food for themselves and by the time they got to 12 weeks after the study no one was in ketosis at all and so that's the major point of the proponents as i understand them as you have to maintain ketosis to to get this improvement in insulin secretion and insulin resistance and so they weren't experiencing that because they were back up to 100 grams of carbs a day which was way less than they were eating before but it wasn't as low as you'd need to be to be in ketosis got it so they were no longer in this situation where they were just running on this fat they were back into this sort of middle ground so christopher one of the the original arguments for um for these sorts of ketogenic diets uh which i think you sort of touched on is people who have diabetes um for whom really their ability to deal with blood sugar is really bad and that there have been these um uh studies showing that if you follow ketogenic diet for uh for a long time that looks like the results are very good is that because actually they managed to be compliant and so that's different from the situation or is that you know most of our listeners are probably not um uh injecting insulin with diabetes so they're in a in a more uh broader range how do we understand are you saying ketogenic doesn't work for anybody are you saying how should we interpret this if you're if you're listening um right now and sort of trying to decide whether to to give this a go so i'll give a practical note here the folks on keto toward the end i think we're better having anchored them so low in added sugar and refined grain i mean for them cheating wasn't a cupcake for them cheating was a piece of whole grain bread right and said whole grain bread that's not cheating that's following the mediterranean diet so god forbid you have a teaspoon of sugar or you have white bread i really think that that anchored them quite well in seeing oh my god i actually had these sugar cravings before i clearly had to go completely off sugar wow it's been a couple weeks and i don't crave sugar as much as i thought so there's some really interesting physiology there so i think there's some potential benefits of seeing how well you could do eliminating all those and keeping up that up long term we're actually doing another mini analysis from our old diet fit study that sort of supports that so anchoring someone psychologically really low so in that regard for the people who are doing ketogenic transiently or temporarily i i could see learning some new things that could be helpful but just from a a taste and a longevity perspective i think a high fat mediterranean diet gives you more options uh easier for social events and so people were really stay sticking with this more is i think just on the on that on that other side the mediterranean diet was just easier to although you said it was a very complex thing it was easier to stick with as a permanent part of your life rather than a temporary diet right and i think you know we all know that diets are basically a bad idea right there's no one who's ever done a diet who believes it's a good idea right that you're saying that the problem with the ketogenic is it's sort of like a diet and this mediterranean is potentially a lifestyle that that you can sustain permanently yeah am i is that right yep and then we saw multiple nutrients that were lower on the ketogenic diet than the mediterranean diet we didn't see any nutrient deficiency symptoms because these are only 12-week diets but long-term if you really did follow this long-term it's such a restrictive diet that there are quite a few nutrients that will be lower on ketogenic and in particular the one that you and i are very interested in is fiber and the microbiome i was going to say can we talk about that for a few minutes because i think um you know i know your study you know there's nothing published yet but i know there's been some other things you know what is the likely impact on the microbiome of a ketogenic diet part of this is a funny story jonathan that we will have to pursue so one of the things that the microbiome produces from digesting fiber is short chain fatty acids and some of those short chain fatty acids are ketones so you could actually get some of the products of what the microbiome would generate from digesting fiber by eating a ketogenic diet on the other hand i have a colleague michael fischbach at stanford who just got a massive grant award to study the molecules that are produced by the microbiome and he has a little graphic of a hundred different molecules we haven't named them all we don't understand what they all do but that's part of the likely effect of the microbiome is digesting the fiber creating small molecules that we absorb that looks like they lower inflammation and improve immune profiles and immune function and those are results that will take a longer study to look at we actually are looking at some of that right now but we're also writing a grant to try to do a longer six or 12-month ketogenic mediterranean type study where we could see longer effects on the microbiome fiber is sure to go down if you exclude all whole grains all fruits so so in your ketogenic group the fiber intake is lower than in the mediterranean group has to be by yes it is yes significant that is the most significant difference of all the nutrient differences and there were a half dozen fiber was the one that stuck out the most so you know you're sort of taking a hit on how you're supporting the microbiome in the hope of you know trying to improve what's going on with your blood sugar which maybe if you have bad diabetes is is a good trade-off but but there's a sort of there's a pretty big cost i think from other studies that we know about the importance of the microbiome even if you you know this study which is sort of shorter term in nature is not going to be able to see that impact is that is that fair am i putting words nope that's perfect getting started on it and you know as well as i it's a complicated issue but we really are pinging away at it we're making some progress we're going to know more soon fantastic and so very final question um which you touched on right at the beginning there are a lot of people who are concerned that if you follow a ketogenic for a while it's going to have some sort of permanent um damage your ability to deal with with carbs and i think this is because there's been a lot of things talked about maybe transient effect on how you you eat carbs when you just switch off uh a ketogenic diet is i mean you would have gone through the ethics i'm sure of doing this study of putting people on the ketogenic diet for 12 weeks did do you have any concerns no no no yeah i mean all the all the molecular metabolic pathways there the enzymes that you're making for digesting they won't go away sorry this reminds me of people who go vegan thinking oh now that i've gone vegan i no longer make the enzymes that digest meat god forbid i eat meat then i won't be able to digest it protein's made of 20 amino acids plants have 20 amino acids animal foods have 20 amino acids you have the same enzymes when it comes to carbs glucose fructose galactose that's all that's there starch long chains of glucose you have these carbohydraces ase stands for enzyme you have they digest carbohydrates you you wouldn't possibly be able to eliminate your ability to digest carbs you would bounce right back so no real concern you know if i think about this as practical advice you know maybe you can't stick with a ketogenic diet but you're not causing yourself any long-term sort of permanent harm by having tried this not for carbohydrate metabolism if as the my partner my division chief as in preventive cardiology saw these folks on keto with ldl sky high if that's adding to atherosclerosis and the plaque that might not be something that you can recover from some of the long-term nutrient deficiencies could be something that you don't recover from but carbohydrate metabolism not a problem bounce right back amazing christopher i'm uh i'm gonna try and summarize what was a a wide-ranging conversation so correct me if i if i get this wrong so uh to start with a ketogenic diet is a diet where you go very low um in carbs that the diet's actually been around for a long time um but only recently have people thought about it as a way that if you wipe out carbs then you can resolve insulin resistance and fix diabetes and from that we started to say well maybe it's a good diet for for everybody in this study where you got people to do both you saw look people lose weight on this ketogenic diet the same as they did on this sort of mediterranean diet that on many of the health measures you saw improvements as well so in that sense can be some positive impact from uh following it however you saw that sustainability of this diet is significantly harder than the sort of broader mediterranean diet that um that you tried and that by the time you were 12 weeks after um after the study actually even the people who are most keen were no longer in this state of ketosis which is where they're just firing off of fat it just wasn't possible to sustain it at the level to give the results that um that are really required it doesn't seem any better than a high quality high carb diet and you have some real concerns particularly i think about certain nutrients and maybe most of all about what it might be doing to your microbiome because you're taking away uh all of these fibers so conclusion with me is like i get to stick with my current zoe diet that lets me indulge in bread in the occasional cake and i don't uh need to move for the ketogenic diet which is good um but that it's very personal and maybe i think that's the final thing that there are individuals who are saying who actually really found it possible to follow this um and so that if there is someone who just this really works great for them then uh you know they might be able to to do that for most of us uh we're probably not going to be able to do it so before we wrap up i've got one final listener question uh from jane on instagram i'd just love to to wrap up with this one because it made me laugh and her question is why is keto popular it's horrendous i think it's click bait i think a lot of people are having fun thinking i i think incorrectly this is my invitation to eat meat and so my takeaway from this is they don't actually understand how keto works keto is high fat it is not high meat christopher thank you so much as always it's so much fun there are so many other things that we could have touched on uh so many of your other studies so uh i'm hoping that you'll come back again and we can talk about some of those as well as some of the the following analysis that comes from this more to come jonathan pleased to be here we'll uh happy to come back sometime soon wonderful thank you christopher thank you to christopher gardner for joining me on zoe science and nutrition today we hope you enjoyed today's episode if you did please be sure to subscribe and leave us a review as we love reading your feedback if this episode left you with questions please send them in on instagram or facebook and we'll try to answer them in a future episode at zoe we want to improve the health of millions by understanding the right food for each of us to improve our health and manage our weight each member starts with an at-home test comparing them with participants in the world's largest nutrition science study if you're interested in learning more about zoe you can head to joinzoe.com podcast and get 10 off your personalized nutrition program as always i'm your host jonathan wolfe zoe science and nutrition is produced by fascinate productions with support from sharon fedder and alex jones here at zoe see you next time [Music] you

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