low carb or fasting? which one is better for weight loss and for health in general? a recent
trial set out to answer this question. it was carried out in China and they recruited 150 men
and women with metabolic syndrome. now, metabolic syndrome, if you're not familiar with it,
is a general metabolic disturbance where you have at least three of: high glycemia,
high blood pressure, low HDL-cholesterol, high triglycerides and abdominal obesity. so if you
have three or more of those, you're said to have metabolic syndrome. in this trial they were mainly
interested in weight loss and improvements to metabolic parameters so it makes sense to start
with a sicker population, if you're looking at a bunch of Olympic athletes you're not going to
see much change, but this varies, some trials do look at healthier younger populations like college
students for example, we've covered some of those before. so they randomly split the participants,
some were put on a low carb diet, some were told to fast. and they had a third group doing
both at the same time. so about 50 people give or take were told to cut back on carbs,
another 50 or so were told to eat in an eight hour window and fast the rest of the day,
and the last 50 did both. now, a couple of specifics, what exactly do they mean by low carb?
this is always a huge Battle of semantics. in one published classification, low carb is considered
under 130 grams of carbs a day which is roughly 26 percent of our daily calories, and that's also
the threshold the American Diabetes Association and other health organizations use, and very low
carb is somewhere around 20 to 50 grams of carbs a day or under 10% of calories. for reference,
in the U.S most people eat upwards of 250 grams a day so this is not a small reduction, the low carb
category would represent a two-fold reduction and the very low carb category would be a five-fold
drop. so they used that threshold of low carb and asked the participants to stay under 130
grams of carbs a day. I know that for some people that's not low carb enough, it has to be the very
low carb range, and for some people that's not low enough, it has to be where you can't smell a carb,
we'll Circle back to this issue of the numbers in the end. the participants maintained their usual
level of physical activity throughout the study, the researchers monitored it and there was no
significant change, which is nice because we can attribute any changes to the diet. a couple more
interesting things about the design, the people who were told to fast were allowed to choose
between early time restricted eating, between 8 AM and 4 pm, and late time restricted eating,
eating between noon and 8pm and fasting the rest of the time. so whatever they preferred in order
to maintain their social schedules. altogether, 70 participants chose the early time window, and
remember we have two groups fasting, right? one is just fasting and the other fasting and doing
low carb. so in total 70 people chose early and 37 chose the late time window, so about two-thirds of
people preferred to eat earlier in the day and skip dinner which is always a little surprising
to me because I'm a huge Night Owl. now, a couple weaknesses of the study, for me the main one is
they didn't record caloric intake so it makes our interpretation a little harder, for some people
that might not matter much, they want to know what works, by hook or by crook matters less, and the
other shortcoming of the trial is it only lasted three months, we looked at other weight loss
trials recently that went on for a year or longer, and the problem with these very short-term trials
is that people usually lose weight initially but then they Plateau or even bounce back,
so short term can give us kind of a rosy picture that doesn't necessarily reflect the long term.
in fact, we can detect this pattern even at their short time scale, body weight went down
on all three groups for the first two months, low carb seemed like a little bit less than the other
two but clearly all are losing weight, but during the third month only the combo group continued to
lose weight, the other two plateaued. at the end of the three months the combo group had lost the
most weight (not that surprising) and the fasting group lost more than low carb (that one I didn't
necessarily expect). now, this is the average of each group, but what happened to each individual?
they report what's called the waterfall plots, which I love, and check out this variation from
person to person. each bar is one individual, and this is a pretty typical pattern in these trials,
if we look at the low carb group for example, most people lost weight, some outliers lost as much as
eight or nine percent of their body weight but overall the average was 2.7 percent body
weight lost. some lost nothing and about 12 people actually gained some weight. this is why it's so
crucial to personalize these things and not be cookie cutter. similar pattern for the fasting
group but a bit more weight loss in average. this Superstar over here lost 15 percent of their body
weight but overall the average was four percent and it looks like five people gained some weight,
and then on the combo group it was even more skewed, average overall was 5.8 percent
weight loss and two people seemed to gain some weight. other indicators of fat loss like waist
circumference, hip circumference and body fat went down on all three groups. one interesting finding
was waist to hip ratio, which is an indicator of abdominal obesity, and only the people on
the fasting group saw a significant reduction of that, they outperformed even the combo Group,
which is interesting. now, as we all know, and you guys point this out in the comments
all the time and I love it, health is about a lot more than just sheer weight loss, so we'll
look at other parameters. one thing that's really interesting, and it's relevant physiologically,
is distinguishing between types of fat, so there's subcutaneous fat which accumulates Under the Skin,
and we all hate it and we grind in the gym to get rid of it, and then there's visceral fat,
which accumulates inside the body cavity around and inside the organs, and that's actually the
most problematic one even though we can't see it in the mirror. so if we had to carry some
extra weight, it's actually better to have it in the love handles than hidden, tucked up inside,
that's the surprising truth of metabolism and physiology. so they measured these two types of
fat and the results are fascinating, all three groups lost subcutaneous fat but only the two
fasting groups lost visceral fat. so fasting alone or fasting plus low carb, but not low carb alone.
also, it was specific to the eating window, the people eating early in the day, the early birds,
had reduced visceral fat and subcutaneous fat, those eating later in the day had no significant
reduction. in my face, I guess. joke's on me. next they looked at other metabolic parameters Beyond
weight and fat, like lipids, glucose and blood pressure. glucose may be the most surprising
finding of all, only the two fasting groups significantly reduced fasting blood glucose,
low carb alone did not, we'll come back to why. uric acid was similar, only the two fasting groups
saw an improvement. hemoglobin A1c, glycated hemoglobin, was even more extreme, only the combo
group saw a significant Improvement. on the other hand, all three groups saw a reduction in fasting
insulin and insulin resistance. so in general the combo group tended to see the most impressive
improvements, not a huge surprise, I guess. and the other finding they reported was that most
metabolic parameters like insulin resistance for example correlated better, they tracked better,
with visceral fat than subcutaneous fat, which makes perfect sense based on everything we know.
okay, what about lipids? kind of similar to what we've seen so far, only the two fasting groups
lowered triglycerides significantly and only the combo group raised HDL-cholesterol significantly.
now, before people start fighting viciously in the comments, none of this means that low-carb diets
don't work. of course low carb diets can lower glycemia, can lower triglycerides, lots of people
have experienced that and that's been published extensively. it just means the specific protocol
they used didn't work as well as the fasting in this experiment, for this specific population.
and we'll come back to this in the end and to what this all means. okay, they also measured
LDL-cholesterol and it was raised on the two groups doing low carb, low carb alone and low
carb plus fasting, and it was not significantly changed on the fasting group. we've looked at
this specifically in many previous videos, it's not a necessary occurrence on low carb diets,
it depends on how the diet is designed. and finally they looked at blood pressure,
and the only significant change was to diastolic blood pressure, which is that lower value in your
reading, and that was lower only on the combo and only for people eating earlier in the day,
not the late birds. okay, let's talk interpretation, what does this all mean?
well, the simple interpretation would be that the combo wins,
tends to get the most impressive changes. okay, but let's look under the hood and see if we can
get some deeper realizations. first thing we have to think about with these trials is compliance,
that's always the nightmare element because we're not dealing with rats in cages, people
do whatever they want, right? so you're trying to gage compliance and then see what we can glean.
they estimated that the people in the fasting group were compliant for about 66 days average.
that's out of 90 total, right? three months. so not amazing, not horrific either. two-thirds of
the days they stuck to it. low carb was worse, 55 days out of 90. so is that good or bad? it's more
productive to think in terms of what we can learn rather than these simplistic labels, so it tells
us that this population had a harder time cutting carbs than restricting their eating window. it
also provides a possible explanation for why low carb had in general less impressive changes. no
diet on earth works if you're not doing the diet. remember this took place in China where the usual
diet is pretty high in carbohydrate. so you're asking a Chinese population to not eat rice,
not eat noodles, not eat dumplings, not eat rolls, not eat potatoes. it's not a small ask.
in comparison, their Baseline eating window was about 10 hours give or take,
so asking them to cut back to under eight hours is not that big a deal. and finally, the combo
group was intermediate, 58 days compliance. okay, what about compliance for the two eating windows?
big difference there. for the people eating early, 61 days average compliance, for the late birds,
75. so in general people found it a little easier to eat later in the day, so I guess I'm not that
weird. it was also impressive that the early eating window had the best results in general
even though the compliance was worse, so if the compliance had been similar, the difference in
improvements might have been even more glaring. now, silver lining, 98% of the participants who
completed the trial said they would be willing to continue on the programs. and that's both for low
carb and fasting, so 98% each. so that's pretty impressive. is it all lip service because they
know the trial is over so they're just going, yeah yeah I'd be willing to continue, sure...
probably not entirely because it was lower for the combo group, only 82 percent.
so the combo is more effective but it's more of a strain to stick to. makes sense. now let's go
back to this issue of the definition of low carb. leaving aside the semantics, how much carbohydrate
did they actually eat? the people in the low carb group ate less than half of the carbohydrate of
the ones who were fasting. they cut rice by more than 50 percent, flour by more than 50 as well,
refined carbs like bread and cookies they cut out entirely. so those are not subtle reductions. on
the other hand, the average carbohydrate intake was between 140 and 150 grams a day, so most
people did not stay under 130 as requested. so going back to that classification we saw earlier,
I wouldn't in all rigor call this a low carb diet, calling it a moderate carb diet might be
more accurate. and this is something we see very consistently, it's not specific to low carb, we
see this with low-fat trials too, it's really hard to get a population to comply to these reductions
and the more radical the diet the harder it is. of course we can always find somebody who's really
motivated and really gung-ho, some people even do better when it's something's really strict,
they do better under pressure, but for a general population, Public Health-Wise, this is a massive
hurdle. this compliance issue can also create a lot of vitriol among online communities because
those select for people who can stick to these things long term so we often see online people
advocating for very low-fat diets or very low carb diets for everyone. "everybody should be on it
because it worked so well for me". yeah but you're a Unicorn, it's not the norm. it's very difficult
to issue wide recommendations based on very strict diets. the other question that's really
interesting is if there's a special threshold for fat intake or carb intake where if you cross that,
you get some special benefits. with carbohydrate there's the obvious threshold of ketosis in very
low carb settings, so this really interesting trial compared a ketogenic diet to a low carb
but not ketogenic diet matched for calories. so five percent of calories coming from carbs in
the keto diet and 15 in the low carb non-keto, and both worked equally well for weight loss, fat mass
and a number of parameters, so there doesn't seem to be a special effect of ketosis independent from
calories, but there's also a lot of evidence that ketones can help suppress appetite so it seems to
be one tool to achieve satiation, and certainly a lot of people report that keto finally allowed
them to maintain a healthy body weight for the first time in their lives and nothing else worked
for them. and this issue of personalization is so crucial. if we look back at the waterfall plots,
none of the three interventions worked for everybody and all three worked well for some
people. look at the low carb data for example. I'm pretty sure this person improved all of
their parameters. they lost almost 10 percent of their body weight. they probably did have
lowered glycemia, lower triglycerides, lower blood pressure. all of these people did pretty well.
but if we told everybody indiscriminately that low carb is the only path or fasting is the only path,
we'd be doing these folks a huge disservice. even the combo wasn't great for a few people,
and remember this is only three months, the challenge is finding something that works for
life. so if a low carb diet works great for you to maintain a healthy body weight and nothing else
has worked, I think medically the right advice is to stick to a lower carbohydrate dietary pattern
and optimize it to fit your personal needs and to support long-term health. and on that note, we
have some really exciting videos in the pipeline with guests who specialize on low carb diets,
we're going to cover tips and tricks to design low carb diets to be as healthy as possible
so stay tuned, let me know your questions below, take care, I'll see you next week