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Are carbs bad for fat loss? Learn whether carbohydrates actually make you gain body fat, if you need to cut carbs to lose weight, and what really matters when creating a successful calorie deficit.
In this video, expert nutritionist Dr Richie Kirwan breaks down the science behind carbohydrates and weight loss, explaining why carbs aren't automatically fattening and whether low-carb diets have an advantage for fat loss.
Key Facts:
Carbohydrates do not automatically cause body fat gain.
Fat loss requires a consistent calorie deficit over time.
You can eat carbohydrates and still successfully lose body fat.
Carbohydrates provide an important source of energy, particularly for exercise and high-intensity training.
Low-carb diets can help some people lose weight, but they still rely on creating a calorie deficit.
Choosing high-fibre, nutrient-dense carbohydrate sources can help with fullness, nutrition, and training performance.
FAQ:
Q: Are carbs bad for weight loss?
A: No. Carbohydrates can absolutely be part of a successful fat-loss diet as long as you're maintaining an overall calorie deficit.
Q: Do carbs make you gain fat?
A: Eating carbohydrates does not automatically cause fat gain.
Consistently consuming more calories than your body uses is what drives increases in body fat over time.
Q: Do I need to cut carbs to lose weight?
A: No. Reducing carbohydrates is one way some people lower their calorie intake, but it isn't a requirement for fat loss.
Q: Is a low-carb diet better for fat loss?
A: Not necessarily. When calories and protein are appropriately controlled, low-carb diets don't have a unique fat-loss advantage simply because they contain fewer carbohydrates.
Q: What carbs should I eat when trying to lose fat?
A: Foods such as whole grains, potatoes, fruit, vegetables, beans, and other high-fibre carbohydrate sources can all fit into a balanced fat-loss diet.
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Show More Show Less View Video Transcript
0:00
Everyone knows that eating too many
0:01
carbs makes you fat, right? It's why
0:03
low-carb diets have become so popular.
0:05
It's why bread is usually the first
0:06
thing to go when someone goes on a diet,
0:08
or why people still act like eating a
0:09
bowl of rice is basically a crime
0:11
against their waistline. But, are carbs
0:14
actually the problem? Or have we been
0:16
blaming the wrong thing this whole time?
0:22
>> [music]
0:22
>> How's it going, guys? My name is Richie
0:23
Kirwan. I'm a registered nutritionist,
0:25
researcher, and university lecturer in
0:26
nutrition and exercise physiology. In
0:28
this video, we're going to look at what
0:30
the evidence actually [music] says about
0:32
carbohydrates and fat loss. We'll go
0:34
through why carbs became public enemy
0:36
number one, what the science actually
0:38
shows, and whether you need to fear the
0:40
bread basket or not. To understand why
0:42
carbs got such a bad name, you need to
0:45
go back a few decades. From the 1970s
0:48
through the 1990s, [music] dietary fat
0:50
was the villain.
0:51
The idea was that eating fat made you
0:53
fat. Governments ran with this idea.
0:56
Food companies ran with it even faster,
0:57
and suddenly everything was low-fat.
1:00
Fat came out of food, and to make it
1:02
taste like something other than
1:04
cardboard, sugar and refined
1:05
carbohydrates went in. But, obesity
1:08
rates kept [music] climbing anyway.
1:10
And people started looking for a new
1:12
explanation. Enter the
1:14
carbohydrate-insulin model.
1:16
The idea is a little something like
1:17
this. You eat carbs, your blood sugar
1:20
rises, your body releases insulin, and
1:22
insulin promotes fat storage. So, if
1:25
carbs drive insulin, and insulin drives
1:28
fat gain, then carbs are the root cause
1:30
of weight gain. Cut the carbs, lower the
1:33
insulin, lose the fat. Seems [music]
1:35
like a super clean, simple, and logical
1:38
explanation, right? And to be fair, the
1:40
mechanism behind the idea is real.
1:42
>> [music]
1:43
>> Carbohydrates do raise insulin, and
1:45
insulin does play a role in fat storage.
1:47
[music]
1:48
The problem is the conclusion being
1:49
drawn from that mechanism, that carbs
1:51
therefore cause obesity, just doesn't
1:54
hold up when you test it in the real
1:57
world, and we have tested it a lot. But,
2:00
before we get into the evidence, let's
2:01
talk about some real-world [music]
2:03
population data. Because this is where
2:05
carbs cause obesity argument starts to
2:08
fall apart very quickly. According to a
2:11
2024 analysis published in The Lancet,
2:13
which pulls data from over 3,600
2:16
studies across 200 countries, around 16%
2:20
of adults worldwide were obese [music]
2:22
in 2022, a number which has more than
2:24
doubled since 1990. So, obesity is
2:26
clearly a growing public problem. But,
2:29
it's not growing evenly. Japan has one
2:31
of the lowest obesity rates of any
2:33
developed country in the world at less
2:36
than 5% of the population. Compare that
2:38
to the UK at around 28% or the United
2:40
States at 40%. That's a massive
2:43
difference. Now, here's the interesting
2:44
part.
2:46
Japan also has one of the highest
2:48
carbohydrate intakes of any [music]
2:49
developed nation. Because carbs make up
2:52
about 57 to 60% of total energy intake
2:54
based on Japan's [music] National
2:56
Nutrition Survey data. On the other
2:57
hand, adults in the US get around 46 to
3:00
47% of their energy from carbs, and the
3:02
[music] UK is pretty similar. So, the
3:03
developed country with one of the
3:05
highest carbohydrate intakes has a
3:07
fraction of the obesity rate of
3:09
countries eating a lower proportion of
3:11
carbs. Now, it's also worth pointing out
3:12
that the average Japanese person
3:14
consumes on average around 240 fewer
3:16
calories per day than the average
3:18
American. [music] And that, as we'll
3:20
see, is going to help explain what's
3:23
going on. To really understand why the
3:25
carbs cause obesity argument doesn't
3:27
hold up, I want to take you back to the
3:29
1940s. Because there's a story from that
3:31
era that I think is pretty cool, and it
3:33
directly goes against everything the
3:35
low-carb world would have you believe.
3:37
Walter Kempner was a physician working
3:39
at Duke University in North Carolina.
3:41
He'd been developing a treatment for
3:42
patients with severe high blood pressure
3:44
and kidney disease, conditions that in
3:45
those days were often a death sentence.
3:48
All of these patients also had
3:50
overweight or obesity, and today we'd
3:51
class them as having metabolic [music]
3:53
syndrome. The treatment he came up with
3:55
was, to put it mildly, unusual. He put
3:58
his patients on a diet that was almost
4:00
entirely white rice and a little fruit.
4:02
That's it.
4:04
White rice, fruit, fruit juice, and a
4:07
little sugar, funnily enough. No meat,
4:08
no dairy, very little salt, and almost
4:10
[music] no fat. Over 90% of the calories
4:13
on this diet came from carbohydrates. If
4:16
you handed this meal plan [music] to
4:17
most people in the fitness world today,
4:19
they'd have it straight back to you and
4:20
tell you it was going to send their
4:21
insulin sky-high and make them gain
4:23
[music] weight. But, something
4:24
unexpected happened. Not only did
4:26
patients' blood pressure improve
4:28
dramatically, they also lost significant
4:31
amounts of body weight, consistently
4:34
across hundreds of patients, published
4:36
across multiple studies throughout the
4:38
late 1940s [music]
4:40
and into the 1950s. Now, Kemper wasn't
4:43
trying to create a weight loss diet.
4:44
[music]
4:45
That was more of a side effect, but a
4:46
side effect that was hard to ignore.
4:48
[music] The diet, built almost entirely
4:51
on carbohydrates, the very macronutrient
4:52
that supposedly drives fat storage and
4:54
weight gain, was producing reliable,
4:57
meaningful weight loss in real patients.
4:59
And the reason,
4:59
>> [music]
5:00
>> when you think about it, is actually
5:01
pretty straightforward. By stripping the
5:03
diet down to such a narrow [music] range
5:05
of foods, patients ended up eating far
5:08
fewer calories overall. Not because of
5:11
anything biochemically special about
5:13
rice or because of insulin, which would
5:15
have spiked temporarily after every
5:17
meal, [music] and not because of any
5:19
metabolic tricks, either. Just fewer
5:21
calories in than out. So, the rice diet
5:24
is a pretty cool story, but it was done
5:27
a long time ago, and Kemper wasn't
5:29
running controlled experiments. So,
5:31
let's look at what happens when you test
5:33
this a little more scientifically. One
5:36
of the best controlled studies comparing
5:37
high-carb and low-carb diets was run by
5:39
Kevin Hall at the National Institutes of
5:41
Health in the US. His team took 19
5:44
people with obesity and put them in a
5:46
metabolic ward, meaning they lived in
5:48
the research facility and every single
5:50
calorie they ate and [music] burned was
5:53
monitored with incredible precision.
5:55
Both groups ate the same number of
5:57
calories and the same amount protein.
5:59
The only difference was the ratio of
6:02
carbohydrates to fat. So, what happened?
6:05
Well, the low-carb group saw their
6:07
insulin drop by over 20% exactly as the
6:10
carbohydrate-insulin model would
6:11
predict. Their fat burning also
6:14
increased significantly. But, here's
6:16
where it gets interesting.
6:18
When the researchers calculated how much
6:20
of that fat burning was actually coming
6:21
from body fat as opposed to the fat they
6:24
were eating from their diet, the
6:26
low-carb [music] group was burning
6:27
around 53 g of body fat per day. On the
6:31
other hand, the high-carb, low-fat group
6:33
was burning 89 g of body fat per day.
6:36
So, despite lower insulin and despite
6:39
higher fat burning overall, the low-carb
6:41
group was actually burning less body fat
6:44
than the high-carb group. explanation
6:46
for this [music] is the low-carb group
6:47
were eating more fat and had to burn
6:50
through that, too. [music] Then, there's
6:52
the DIETFITS trial run by Professor
6:53
Christopher Gardner at Stanford
6:55
University in the US, which is one of
6:56
the largest and most rigorous
6:58
free-living diet studies ever conducted.
7:00
Over 600 participants were randomly
7:02
assigned to either a healthy low-fat or
7:04
a healthy low-carb diet for a full year.
7:07
And the result? Both groups lost a very
7:09
similar amount of weight. The low-carb
7:11
group lost around 6 kilos and the
7:12
low-fat group lost around 5.3 kilos.
7:15
That's a difference of about 700 g over
7:17
a year, which isn't statistically
7:18
significant and which could easily be
7:21
explained by differences in water loss
7:23
since we know low-carb diets cause
7:25
greater water loss early [music] on. So,
7:27
again, no major differences between
7:28
low-carb and low-fat. And it's not just
7:31
these two studies. A major meta-analysis
7:34
published in The Lancet, which pulled
7:36
results from 53 studies involving over
7:39
68,000 [music]
7:41
participants, found that low-fat,
7:43
high-carb diets, and other dietary
7:45
approaches, including low-carb, produced
7:48
almost identical amounts of weight loss
7:51
over 12 months. So, the evidence, when
7:53
you look [music] at it in its totality,
7:55
is really, really consistent. It doesn't
7:57
matter much whether the calories come
7:59
from carbohydrates or fat. What actually
8:02
matters is how many calories are
8:04
consumed overall. Now, at this point,
8:06
some of you are probably thinking,
8:07
"Okay, fine. Maybe carbs in general
8:09
aren't the problem, but what about
8:11
sugar?" Because sugar is different,
8:13
right? Fructose in particular gets a lot
8:15
of attention because, unlike glucose,
8:17
it's metabolized [music] primarily in
8:18
the liver, and at high doses in animal
8:21
studies, it can cause all kinds of
8:23
metabolic [music] problems. So, the idea
8:25
is that sugar causes weight gain through
8:28
some sinister mechanism that operates
8:30
completely separately from calories. It
8:33
sounds logical, right? So, let's look at
8:35
what the evidence actually shows. A
8:37
systematic review and meta-analysis
8:38
published in the Annals of Internal
8:40
Medicine by Sievenpiper et al. looked
8:42
specifically at what happens to body
8:44
weight when you feed people high amounts
8:46
of fructose in controlled conditions.
8:48
They pooled the results of 41 controlled
8:50
feeding trials in total. In 31 of those
8:52
trials, fructose was swapped in for
8:54
other carbohydrates while keeping total
8:56
calories the same. So, what happened?
8:58
[music]
8:59
Essentially, no difference in body
9:01
weight whatsoever. Fructose, when it
9:03
wasn't adding extra calories to the
9:05
diet, didn't cause weight gain. Now, in
9:08
the other 10 trials, participants were
9:10
given fructose on top of their normal
9:12
diet, providing excess calories. [music]
9:15
And in those trials, people did gain
9:17
weight. Big surprise, right? Now, here's
9:19
something pretty interesting.
9:21
The dose of fructose being used in those
9:23
trials were between 104 and 250 g of
9:28
pure fructose per [music] day. Table
9:29
sugar is roughly 50% fructose. So, the
9:32
lower end of that range is equivalent to
9:34
eating the fructose from around 52 tsp
9:37
of sugar every single day on top of
9:40
everything else you normally eat. That's
9:42
just not a realistic diet. These are
9:45
studies specifically designed to
9:47
force-feed people a huge amount of
9:49
fructose and even then
9:51
>> [music]
9:51
>> the weight gain seen was around half a
9:53
kilogram, an amount entirely consistent
9:57
with just eating too many calories
10:00
regardless of where those calories come
10:02
from. The authors of the review were
10:04
pretty clear about the conclusion, too.
10:05
>> [music]
10:06
>> Fructose doesn't appear to cause weight
10:07
gain when it replaces other
10:09
carbohydrates in the diet. When it does
10:11
lead to weight gain, it's because of the
10:13
extra calories, not [music] anything
10:14
biochemically unique about fructose
10:17
itself. So,
10:18
if carbs aren't uniquely fattening and
10:21
if cutting carbs doesn't produce any
10:23
specific metabolic advantage, why do so
10:25
many people lose weight on low-carb
10:27
diets?
10:28
Because they clearly do. The answer is
10:30
actually pretty straightforward and it
10:32
comes back to the same thing we keep
10:34
returning to throughout this video.
10:36
Calories. When people go low-carb, they
10:39
typically cut out a huge range of foods
10:41
all at once. That's [music] a
10:42
significant chunk of what many people
10:45
eat on a daily basis [music] and unless
10:47
these foods are carefully replaced with
10:49
something else,
10:51
calories drop. Not because of anything
10:53
special about carbohydrates, but simply
10:55
because the overall variety of food
10:58
available to eat has been dramatically
11:00
restricted. This is sometimes called
11:02
spontaneous calorie reduction and it's
11:05
well documented in research. It's also,
11:07
incidentally, exactly the same reason
11:09
other restrictive diets work, whether
11:12
that's low-fat, vegan, or
11:14
>> [music]
11:14
>> any other approach that cuts out a
11:16
significant category of food. The
11:18
dietary pattern changes, the calorie
11:20
intake drops, and people lose weight.
11:22
There's also a protein effect worth
11:24
mentioning here. Low-carb diets tend to
11:26
[music] be higher in protein and protein
11:28
is by far the most satiating
11:30
macronutrient. It keeps you feeling
11:32
fuller for longer and reduces overall
11:35
appetite. So, people on low-carb diets
11:37
often end up eating
11:38
>> [music]
11:38
>> less without consciously trying to,
11:40
which again leads to a calorie deficit.
11:42
Now, don't get me wrong. Low-carb diets
11:44
are a perfectly valid tool for fat loss.
11:48
If cutting carbs helps you eat less and
11:50
stick to a diet, then it's a good
11:52
strategy for you. But, it works because
11:54
of the calorie deficit it creates, not
11:56
because of anything magical happening
11:59
with your insulin. So, we've established
12:01
that carbs don't cause fat gain, that
12:02
calories are what actually drive it, and
12:04
that any diet works primarily by
12:06
creating a calorie deficit. But, here's
12:08
something that doesn't get talked about
12:09
nearly enough in this debate. And I
12:11
think it's one of the most practically
12:13
useful things in this entire video. Some
12:16
carbohydrate-containing foods are
12:17
actually among the best tools you have
12:20
for controlling your appetite [music]
12:21
and making a calorie deficit easier to
12:24
sustain. And that comes mostly down to
12:26
fiber. Fiber is technically a
12:28
carbohydrate, but it can't be digested
12:30
by the enzymes in our gut.
12:31
>> [music]
12:32
>> And that indigestibility is exactly what
12:34
makes it so useful. A systematic review
12:35
of randomized controlled trials
12:37
published in Obesity Reviews found that
12:39
higher dietary fiber intake consistently
12:41
[music]
12:42
reduced appetite, energy intake, and
12:44
body weight. The effect was particularly
12:46
strong for viscous fibers, the kind that
12:48
absorb water and form a gel in your gut,
12:51
slowing digestion and keeping you fuller
12:53
for longer. [music] You can find viscous
12:55
fibers in foods like oats, barley, rye,
12:57
beans, and lentils.
12:59
All of which are, of course,
13:01
high-carbohydrate foods. Think about
13:03
what a bowl of porridge does for your
13:04
hunger compared to the same number
13:06
[music] of calories coming from a slice
13:07
of white bread. Both are mostly carbs,
13:09
but the fiber in the oats slows
13:11
digestion, creates volume in your
13:13
stomach, and blunts hunger in a way that
13:15
[music] refined carbs simply don't. Now,
13:18
that's not a reason to avoid sugar
13:20
entirely, but it is a really good reason
13:22
to think carefully about where the
13:24
majority of your carbs are coming from.
13:26
Whole grains, legumes, fruits and
13:28
vegetables are all carbohydrate-rich
13:30
foods that also happen to be high fiber,
13:32
relatively low in energy density, and
13:35
genuinely good at keeping hunger under
13:37
control. So, these aren't foods that
13:39
make fat loss harder. If anything,
13:41
they're foods that make it easier,
13:43
especially if you combine them with lean
13:45
protein [music] to really max out the
13:47
satiety effect. And one last thing about
13:50
carbs that's worth mentioning, [music]
13:51
they can really help with how you
13:53
perform in the gym. You don't need them
13:55
by any means to lift weights, but they
13:57
can make lifting weights feel a little
13:58
bit easier and a little more pleasant,
14:00
to be honest. Considering most people
14:02
who are trying to lose weight are
14:03
probably exercising pretty regularly,
14:05
too. Making the whole experience a
14:07
little more pleasant [music] by having
14:08
some carbs is probably a good idea. So,
14:11
after all that, I hope you've realized
14:13
that the question shouldn't be, are
14:15
carbs bad for fat loss? The more useful
14:17
question is, which carbs
14:19
>> [music]
14:19
>> and in what context can help with fat
14:21
loss? And the evidence suggests that
14:23
whole food, high fiber carbohydrate
14:25
sources can [music] be some of your best
14:27
allies when it comes to managing your
14:30
weight long-term.
14:31
>> [music]
14:31
>> If you have any questions about carbs
14:32
and fat loss, let me know in the
14:33
comments below. And if you found the
14:35
video useful, make sure to hit the like
14:36
button and subscribe to the Myprotein
14:38
YouTube channel for more great,
14:39
evidence-based nutrition information.
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