there's a new randomized trial comparing vegan diets and omnivore diets but this trial has a
twist, they looked at identical twins, one on each diet. there have been some media pieces in the
past like this, a pair of twins, one on each diet, and what happens to them. so this is like that
but on steroids because the twins are randomly allocated to the diets and it's 44 twins, so 22
pairs of identical twins. now, very important point, both diets are designed to avoid ultra
processed foods, added sugars, refined grains. so they're healthy versions of vegan and omnivore.
so both had vegetables and fruits and legumes and things like that and then the omnivore had animal
products on top. the study lasted two months, for the first month they had all the food delivered
to them for free and during the second month they were expected to spread their wings and fly and
start buying their own food. a lot of people asked about the duration. two months is a short trial,
it's enough to see changes in biomarkers, things like glucose levels, cholesterol levels, some
body weight changes, but obviously you're never going to get information in terms of who gets a
heart attack or not, who goes on to have cancer or not, you're never going to get that from a trial
that doesn't last several years, so this trial by definition can't address long-term effects. okay,
so what happened, what were the results? after those two months, the twins that were allocated
to the vegan diet experienced a larger drop in LDL-cholesterol than the twins on the omnivore
diet. so LDL-cholesterol was in the 110s before the trial, there was no significant drop in the
omnivores and it dropped by about 14 points in the vegans. fasting insulin, also a bigger
drop in the vegans, roughly a 17% reduction, and finally body weight, there was about a kilo and
a half of body weight loss in the vegans, and no significant difference in the omnivores. and fat
mass and lean mass were not measured, or at least not reported, so we don't know what the breakdown
of body weight loss is. in terms of making sense of these results, the weight loss would explain a
lot of it, certainly the drop in fasting insulin, that's very common to see with weight loss,
which is really interesting because we sometimes have this idea that insulin levels are all about
the carbs we eat, the reality is not that simple, in fact the twins on the vegan diet if anything
were eating a bit more carbohydrate than the twins on the omnivore, so that clearly doesn't explain
the changes in insulin levels, of fasting insulin, but the weight loss could and it's a perfectly
plausible explanation. the weight loss might even explain the changes in LDL-cholesterol, or at
least part of it. the vegans were also eating less saturated fat, they actually cut their saturated
fat intake in half compared to before the trial so that also likely had an impact. and intake of
fiber is another factor that might have played a role. so why did they lose weight? one obvious
question, how many calories were they eating? they were getting about 2,000 calories a day before and
this came down to 1,800 in the omnivores and 1,600 in the vegans. several people asked about this
calorie aspect, why wouldn't the investigators keep the calories constant for everybody, doesn't
this skew the entire study? well, you can design a study to answer different experimental questions,
and neither one is right or wrong, so you can keep the calories constant, what's called an isocaloric
study, and there you're basically asking what is the calorie-independent effect of this diet? if
on the other hand you let them eat as much as they want, what's called ad libitum, then you're asking
a different question, you're saying, in the real world, without investigators telling them how much
to eat, how much of each diet are they going to eat, are they going to lose weight or not,
so they're different questions, neither one is right or wrong, they're both interesting,
it depends what you want to investigate. they also measured a number of other parameters:
HDL-cholesterol, triglycerides, B12 levels and fasting glucose levels were not significantly
different. the B12 trended down in the vegans but it didn't reach statistical significance, and I
don't think they were supplementing, according to the study it doesn't seem like they were. now,
this was only two months so it's not a huge deal, we have reserves that normally last for
much longer than that. I probably would still have supplemented but certainly anyone doing a vegan
diet for a longer period of time it's crucial to supplement B12. TMAO, which is a metabolite you
can measure in the blood, also trended down in the vegans but it was not statistically significant,
and then the authors did what's called a sensitivity analysis, basically they took out a
couple of outliers, people who had extreme values, and then the levels became significantly lower in
the vegans. now, the evidence I've seen for TMAO points to TMAO being an an indicator of animal
product consumption but not an agent of risk, not a cause of risk per se. so I'm not particularly
worried about TMAO levels but I'm open to other data in the future that might contradict that.
now, all the press about the study mentions biological age, that they measured it and it
was a little bit lower in the vegans, and they say it was the most interesting finding of the study,
but it wasn't included in this publication, and so I talked to Christopher Gardner,
the senior author, and they plan to publish it separately at a later date. I'm just saying this,
just explaining why you might see in the press this reference to biological age and
them referring to it as the most most interesting finding of the study and you might ask, why is
this video completely ignoring that? well, because it's not out yet, I haven't seen those data. now,
in these diet studies it's always crucial to ask, okay, what did the participants actually end up
eating, what was the intake of different foods and different nutrients? one thing that's meaningful
is protein, the participants were getting about 77 grams of protein a day before the trial,
it became 90 grams a day on the omnivore diet and 57 on the vegan diet. so 57 is on the low end,
I actually did the math based on their average body weight, 57 would be right on the RDA, and
this is the average, right? so some people might be below that, and there's some controversy around
this but there are a number of protein researchers who argue that the RDA is already lowballing our
need for protein so there's a possibility here that some of these people weren't getting enough
protein depending on activity levels and all that. in terms of their intake of grains,
there was an improvement. before the trial the participants ate mostly refined grains,
pretty typical for a US population. during the trial there was a drop in refined grains, a bit
more in the vegans but both came down, and when they went back to buying their own food in the
second half of the study, this will probably not shock you, refined grains bounced back up. a bit
more in the vegans. neither one went back quite to the level before the trial but there was some
bounce back. and then animal product intake, the omnivores actually increased their animal product
intake during the trial compared to before, they almost doubled it. and the vegans as expected went
to zero or close to zero so there was a very nice separation between the groups. they also reported
what they called diet satisfaction, their general experience with the diet, and it was unchanged in
the omnivores and it was actually reduced in the vegans. and the difference was mainly in
their eating out experience, they found that less satisfying. not exactly super surprising,
they probably had a hard time finding something that fit their diet restrictions, everybody else
is eating a different thing that they can't eat, not shocking I guess. at the end of the study,
after the two months, they asked the participants if they planned to continue on the same diet, and
this is really interesting data, in the vegans 5% said yes, closely, I plan to continue rigorously.
5% said no way Jose, they're going right back to how they were eating before the trial. and
the remaining 90% said they want to stick to some of the changes but not all. in the omnivore group
it was 28% stick closely, 5% go right back and 67% continue some but not all of the changes. so this
clearly points to a more likely adherence for the omnivore group, at least for these formulations,
these diets that they used. now, some of the difficulties, some of the specific barriers
that they noticed that made it harder for them to stick to the diets and that were more often
mentioned by the vegans included not liking the foods, taking longer to prepare, the foods being
unfamiliar to them, being too big a change and not fully satisfying their hunger. this difficulty
with adherence, I didn't find this surprising at all, we see this very consistently in trials
where people are asked to make large changes to their diet, whether it's very low fat diets or
very low carb diets or vegan diets, we see this very reproducibly in trials, most people seem to
struggle to maintain these substantial dietary shifts, that's just the reality for most humans.
so this points to the importance of finding ways to eat healthy that are satisfying for you,
otherwise people just don't stick with it long term and they go back to eating whatever they were
eating before. and it clearly doesn't need to be the same recipe for everybody, we see that even in
these results, there's a distribution, right? some people are fine with it, some hate it, some in the
middle. and I know we have vegan viewers, low-fat viewers, low carb viewers, who say that they don't
find it a struggle at all, they find it enjoyable and easy, so phenomenal, you found the right fit,
the right marriage for you. so to summarize, this study points to some common principles
of nutrition that we've covered here many times with this added twist of the twins that is really
interesting because it takes out of the picture the genetics confounder, right? the findings
are probably due to the dietary differences since there's no genetic difference between
the twins. so some of those key principles are sustainability, the importance of finding a diet
that you find doable in the long run. for people who prefer to not eat any animal products, keeping
an eye on your protein intake, make sure you get some protein-rich foods, and also a good source of
B12 is essential. for those who prefer omnivore diets, keeping an eye on these cardiovascular
disease metrics like LDL-cholesterol and others, and for both, regardless of specific diet choice,
favoring whole foods and going easy on ultraprocessed foods, refined grains and
added sugars. that helps a lot with maintaining healthy body weight. if you want to see two other
diets compared, keto and Mediterranean, we have a video on that. and here's everything
you need to know about vitamin B12 in 10 minutes. check those out, I'll see you next time, bye bye