Aidan:
Hello and welcome to the Ideal Nutrition Podcast. My name is Aidan Muir and I’m here with my co-host, Leah Higl and this is episode 144, where we’re going to be talking about the Netflix documentary, You Are What You Eat, a twin experiment. We’re going to be talking a little bit interchangeably between the documentary and also the study that was based on to give a bit of context about everything and to share our thoughts on it.
Leah:
So starting with what the study actually was, what it involved. So essentially the researchers got 22 sets of twins, so 44 participants in total, and had the aim of comparing a vegan diet to an omnivorous diet. So the study itself is titled, Cardio Metabolic Effects of Omnivorous versus Vegan Diets in Identical Twins. So a pretty interesting study set up.
It was a randomised control trial with a timeframe of eight weeks in total. So the first four weeks, all the participants had delivered meals and then the last four were self-made. The overall conclusion was that those consuming a healthy vegan diet showed significantly improved low-density, lipoprotein cholesterol concentration, fasting insulin levels and weight loss compared to the twins consuming a healthy omnivorous diet. So a pretty interesting takeaway as well from that.
Another key factor worth being aware of is the specific wording from the study was, although weight loss was not discouraged, our diet design did not include a prescribed energy restriction and was not intended to be a weight loss study. Participants were just simply told to eat until they were satiated throughout the study and that is important to consider because these people were just eating like ad libitum in terms of their overall caloric quantity and weren’t told to do anything specific.
Aidan:
So we’re gonna unpack that study a little bit before we talk about the documentary aspect Obviously, the main findings was a reduction in LDL fasting insulin and white being more in the vegan group. The weight change wasn’t massive. It was 1.5 kilos different over that eight weeks. A super important part of this conversation is that last bit about how it was ad libitum intake. So it wasn’t like there were a set amount of calories, even though they were being delivered meals at the start. Calorie intake was reported at the baseline and throughout. We know that self-reported data isn’t perfect, but it is useful to see that that was in there. So it can still be helpful.
Calorie intake was around 200 calories lower in the vegan group, according to this reported data, throughout that eight weeks. It was around that amount lower both during that first four weeks where all food was provided and also after they switched to preparing their own food as well. And protein intake also happened to be lower as well. We could talk about that, but we’ll talk more about the differences in diet before we try to like interpret this type of stuff.
Saturated fat was higher in the omnivorous group. I’ve got the data in front of me and saturated fat at the baseline for both groups was about 36% of their total fat intake. At the four-week mark, it was 22% in the vegan group and 29 % in the omnivorous group. And in the self-prepared phase, it was 23 % in the vegan group, 31% in the omnivorous group. So you can see there’s a pretty decent difference there. Fibre intake was significantly higher in the vegan group as well.
They went through and like charted out their insoluble and their soluble fibre intake, but the short version is it was about a third higher. We can go through interpreting that. That is the summary. There’s a big difference in calorie intake, protein intake, fibre intake, and saturated fat intake.
Leah:
Yeah, and I think that leads well into our next part in terms of interpreting the outcomes of the study with those particular variables that were also found. So as an independent variable, we know that reducing saturated fat, and replacing it with things like polyunsaturated fats typically does seem to reduce cholesterol. We also know that a higher fibre intake also contributes to reductions in cholesterol.
And the reduced calorie intake is probably a huge factor here because there was a reduction in body weight that probably does lean into that improvements in fasting insulin and LDL overall. So that can be interpreted in two kind of ways. A, this can be achieved with an omnivorous diet with some additional like specific interventions. So there’s no reason why you can’t take the same omnivorous diet and just simply increase the fiber intake, decrease saturated fat and reduce overall energy intake. Like we would likely see pretty similar outcomes to a vegan diet. So it’s more about these other variables that are changing through people’s food choices being vegan versus not vegan.
Regardless, we typically encourage relatively low saturated fat intake and a high fibre intake, no matter what kind of dietary approach someone chooses, just because we know based on current research that all of these things do contribute to those health outcomes that we mentioned. Most people in general would benefit from eating more plant-based foods, even if they start starting at an omnivorous base, and then also minimising their intake of high-fat meats.
Alternatively, you could look at this and also acknowledge that being on a plant-based diet means that you’re probably way more likely to do those things in terms of having a high fibre intake, reducing your saturated fat, et cetera. On a plant-based diet, particularly when you’re taking a whole-food kind of approach, is that these things just happen. You don’t necessarily need these additional interventions on top of, I guess, your overall approach. So you could say, I’m gonna go plant-based with a whole food focus, or you could say, I’m going to follow an omnivorous diet and then I’m also gonna further reduce my saturated fat intake and also increase my fiber and go into maybe a small caloric deficit for some weight loss. So I feel like the how of just going vegan is a lot easier for a lot of people to do as opposed to thinking of these multiple interventions.
Aidan:
Yeah, I like that summary. That covers a lot of my thinking as well, just being like these same things can be achieved on an omnivorous diet and on a plant -based diet. They made a big focus on how the omnivorous diet was meant to be a, quote on quote, healthy omnivorous diet. So like, they’d made a big emphasis on being like, we aren’t comparing a rubbish omnivorous diet to a healthy plant -based diet. We’re trying to compare life for life. We’re trying to make them both healthy versions. But there are still these differences that we saw in terms of fibre intake, saturated fat, et cetera. And on an omnivorous diet, you could have lean cuts of meat and then the saturated fat intake would likely be significantly lower. I think everybody, there’s a lot of people who should be increasing fruit and vegetable intake, increasing fibre intake. There’s many ways to achieve these things.
That’s basically a summary of the study. Let’s talk about the documentary stuff, because there’s a lot to unpack there.
Leah:
It gets a little stickier.
Aidan:
Yeah. I just watched this for work-related reasons, because I was like, think I’m going to get a lot of questions, obviously. It’d be cool to make some content on this. One of the most interesting things that stood out to me is t really devalued how strictly controlled I think most people would picture a study like this. We will read a line that says something like, food intake was ad libitum. But there were so many bits of the documentary that made me question how that should be interpreted. For example, they were getting DEXA scans at the start and at the end, which is good because we had that data, that’s really great.
But in the documentary, they were being given different advice during the DEXA scans, like there was a set of relatively lean twins at the baseline. And the advice they were given was they were really like the person giving the scan was really pushing them to eat more food to try and build some muscle. There were heavier twins who clearly were not given that same advice and the emphasis of what would be a positive change to them would have been more related to weight loss or fat loss, right? So very different advice. And it begs a big question of is it ad libitum if you were trying to eat more food?
If you feel slightly full, but you’re like, need to eat more food, will you likely try to eat more calories? Is that still quote unquote ad libertum? So that’s just an interesting thing when we’re thinking about how this is meant to be interpreted. Another thing that devalued a little bit as well is like in free living studies, we assume that adherence is not going to be perfect. They did do these moves like giving them pre -prepared meals, which should improve adherence quite a bit. But there’s a few things obviously stood out.
In one scene, as an example of this, there were two twins or a set of twins who were chefs and they were eating stuff at work during the first four weeks when they were meant to be on the pre-prepared meals. And there was a bit of an explanation about that later about how they didn’t follow the plan closely as well, which we’ll probably come back to. But I’m like, it was so interesting just watching that being like, they’re filming this, they’re not commenting on this during the documentary. And it’s like, it’s one thing to be like, I assume people aren’t perfectly adherent. It’s another thing to be like, like, they’re actually filming this right now and not even saying anything about it.
Leah:
Yeah, I guess it’s interesting to see like free living studies actually in action to see how people actually do or do not follow the interventions that prescribed. Although we do have the overall results of the paper, an interesting part of the documentary was seeing, I suppose, some very specific case studies of different sets of twins throughout the process. So there were one set of twins, lean set of twins and they had the DEXA scan pre and post the intervention. And it was pretty interesting to see the difference in lean mass gain that they both achieved during that eight weeks.
So like you said, they were told to eat a little bit more, which they did, and they gained overall weight. The omnivore gained 7.1 pounds of lean mass on a DEXA scan, and the vegan twin gained only 2.3 pounds of lean mass. So if that was interesting to see, obviously there was probably a difference in protein intake, overall calorie intake, but even just seeing the difference in the amount of lean mass eating quote unquote kind of ad libitum was interesting. Another example is a set of male twins that were part of the study.
So the one who was in the vegan group had a young family, moved house multiple times throughout the process during the process of the study, he missed heaps of training sessions and was just doing some typical body weight stuff at home. The omnivore or the one in the omnivore group was lifting consistently in the gym and didn’t have as much going on lifestyle-wise. So when the DEXA showed that both of them had lost weight, an interesting observation here was the omnivore gained lean mass while the vegan one lost lean mass.
And you kind of go, maybe this is omnivore versus vegan, but it might also be just circumstances and training that is playing pretty heavily into that. Then the final case study I’ll talk through is kind of where it gets a little bit worse from, I suppose, looking at the validity of the study overall. But the twins we had previously mentioned that were eating food off plan from their place of work didn’t really follow the protocol.
They stuck to the vegan versus omnivore side of things. So they did that, but they randomly started doing cardio every day. They completely changed their diets from what they were supposed to be doing other than being vegan versus omnivore. And they had a pretty wild result. So the one on the vegan group lost 7.6 pounds of weight, of which only one pound was body fat, which is insane.
Aidan:
That is a wild result.
Leah:
Yeah, that’s actually crazy. And then the omnivorous one lost 3.5 pounds, all of which was lean mass, which again, just crazy result from them.
Aidan:
Yeah. So once again, like going back to this whole control and stuff like that, this kind of devalues that as well, just being like, and we’ll talk about this a little bit later, but like a lot of people have pointed to this study as a bit of a vegan dunking on basically, yeah, there’s a health outcomes. But you hear stuff like that and you’re like, so this one set of twins like we think of as tightly controlled because it’s a twin study It’s like a random set of twins completely change the diet and completely change the training It’s kind of hard to interpret that stuff.
Another set of twins like this is just a common theme like this is just like I think it was like four kind of cases they kind of another the final set that we saw One did heaps of lifting and the other did heaps of walking like they asked her like why she did and she’s like walking is just kind of my mode. Like I’m just kind of into walking. And she lost more lean mass obviously than the one who was lifting. It makes sense. And it just so happens that in all of those cases, like the last three that we mentioned, sorry, the last three that we mentioned, it was the vegan group that happened to lose more muscle, but they were just lifting less.
Leah:
Like, yeah. It’s like they were controlling for obviously the genetic side of things with going for identical twins, but it’s the lifestyle stuff that was completely not controlled.
Aidan:
Yeah. And the whole time I was watching that kind of case study thing, I was thinking about the amount of people I have seen online kind of just pointing to the abstract of this study as if it is a big, big deal. And there are people on both sides looking at different things. People in the omnivorous camp are pointing to the plant-based group plus lean mass. They’re pointing to that.
But you hear us talk through stuff like that and you’re like, how much of that was due to plant -based diets? How much of that was due to not lifting heavy progressive overload structure training, et cetera? It’s really hard to even interpret that based on that. Before we even talk about the fact that protein intake was lower. That’s not really about plant -based versus omnivorous. That is about all those other details. Then there are people in the plant -based group who are talking about stuff like LDL, visceral fat, fast immune system, weight, and TMAO. And there’s like, there’s people on both sides talking about different things.
And those arguments sometimes seem to be based on the fact that the belief that this is very, very tightly controlled. It is super impressive to get 22 sets of twins willing to do a study like this. Like actually think about that for a moment and be like, not only have you found 22 sets of twins, so 44 people, you’ve also found people who are willing to go vegan for eight weeks or stay omnivorous. So you can’t recruit vegans for this study because they wouldn’t be willing to do omnivorous side. Like this is a very hard study to pull off.
So that is super impressive. But on other hand, I just wouldn’t interpret this as if it is some super tightly controlled design, even though twins were used.
Leah:
A really interesting portion of the documentary itself was how much it brought in all of the ethical sides of veganism as well. And we’re talking a little bit off air in terms of it being a little bit vegan “propagandary” from all the other things that they started to bring in. If we want to evaluate the study, that’s one thing. All of this other stuff in terms of environmental reasons for going vegan, animal agriculture, like ethical reasons, it’s kind of, it’s very outside of the scope of looking at the health outcomes of this particular study, but it was something that was heavily focused on in parts of the documentary.
From this ethical perspective, this stuff had like personally for me as someone who is plant-based vegan, pretty close to my heart because it’s ultimately why I went vegan almost a decade ago now. The health arguments for veganism have never really struck a chord with me because I’ve always felt that whether I had an omnivorous diet or a vegan diet, I would be able to maintain a health-promoting diet that also facilitated strength and muscle gains. It’s just how that particular diet was set up. And looking at this study and this documentary, that doesn’t change my opinion.
I still think both can be modified in a way that have very similar outcomes, whether we’re looking from a cholesterol point of view, like metabolic disorder point of view, or if we’re looking from a muscle gain body composition point of view. So when it comes to the ethical side of things, think they made some good points in regards to like, if you don’t like factory farming and the treatment of farm animals, I think that is something that strikes a chord with a lot of people. And that’s more of like a personal choice thing, depending on how you feel. On the environmental side of things, it is pretty clear that like, if we look at the research on the environmental side of things, it’s pretty clear that we’re not able to sustain such a high global consumption of animal products forever, particularly as they are increasing.
So, either way, we probably need to completely revolutionise animal agriculture through things like lab-grown meats and things like exciting things like that that are happening, or we need some pretty big population changes. But I’ve also always been a firm believer in that we need millions of people eating less meat and more plants, not a handful of perfect vegans. So I guess I can sum up my opinion as being like it doesn’t really matter what you do, we probably should all start eating more plants and less meat, but it doesn’t necessarily need to be in the context of 100% veganism.
Aidan:
Yeah, I wanted to leave that section for you.
Leah:
Yeah, I obviously have thoughts about it. I am vegan, I care a lot about this stuff. I see why it strikes a chord with other people. But if we’re just talking about the context of this study and the health outcomes, I think it’s kind of irrelevant.
Aidan:
Yeah, and I like to separate then I like to separate all of the things in terms of like, like to separate nutrition, ethics, environment, etc. Like I like them viewed all individually. I feel like it can get messy when you lump things together. They all matter. But I also think it was really important for us to put that into the podcast because I’ve also seen other people make content on this and then get ripped for not mentioning that even though that was such a huge part of documentary.
Leah:
I mean, like, at the end of the day, we’re a nutrition podcast, so we care about the nutrition and health outcomes, which is why we spent most of the time talking about this. But, you know, here’s your little section on the fact that this stuff does matter. It just depends on who you are and how much you care about it.
Aidan:
Yeah, so summarising the rest of the stuff, I think it was cool that twins were used for a study like this. Twin studies can be really beneficial from a scientific perspective for learning about stuff like this. The one thing that sucks is just because adherence to the nutrition and training was so different, it does kind of reduce the impact of this. The obvious reason why twins are used is to kind of be like, if we get two people with the same genetics pretty much, how does this come out differently? The adherence does change that. But there are a few ways we can look at all of this from multiple angles.
So the same results from my perspective can be achieved on an omnivorous diet for many of these markers when we’re looking at things like body weight, fasting insulin, LDL, cholesterol, you could make debates about TMAO like that is a different kind of discussion, but all those metrics I looked about with body weight, fasting insulin and LDL, you could achieve similar results, right? Then you can look at the other angle and just be like, yeah, it’s easier to achieve these on a plant-based diet. You could say that the ad libitum intake was a weakness because it doesn’t come out the same, or you could say that in the real world, it’s a bit of a strength because it kind of shows what typically happens when we look at these things.
It goes both ways with that. And from the other perspective, because looking at it being like a lot of people interpreted as being like, people on a plant-based diet lost muscle. That could also be avoided on a plant-based diet by using the exact same logic about how as like people on omnivorous diet could eat higher fibre, lower saturated fat. People on a plant-based diet could eat higher protein. They could eat slightly higher calorie than they did in this study as well. You can achieve both things from both perspectives. I think it’s an interesting study, but it doesn’t exactly change the game on that type of stuff because we have so many things looking at this already as well.
Leah:
So would you say it changed your opinion on anything?
Aidan:
Honestly, no.
Leah:
Yeah. No, my opinion hasn’t changed. My opinion hasn’t changed either. So this has been episode 144 of the Ideal Nutrition Podcast. If you haven’t yet left a rating or review, it would be so greatly appreciated for you to do so. But otherwise, thanks for tuning in.