Professor Bart Kay. Optimal Nutrition / Energy / Fats vs Carbs
Kurt Annaheim
Bella & Professor Bart Kay. Optimal Nutrition / Energy / Fats vs Carbs
Transcript:
Bella:
Okay, it looks like I am live. Let me know in the chat if you can
see and hear me—and if you can see Professor Bart K here.
Bart, please introduce yourself to my audience. Welcome.
Bart:
Certainly. I think you already did a fair bit of that, but I’m
Bart K. I was an academic for over 20 years. I worked in 11
different universities across four continents.
I taught various aspects of health science, including the physiology of rest and exercise, human nutrition, and cardiovascular pathophysiology. Alongside that, I developed a strong grounding in statistical inference, research methodology, and ethics.
Over time, though, academia lost its way. It became more about ideology than teaching people how to think critically and logically. So I decided to step away.
Now I work as a consultant, a farmer, and—somewhat reluctantly—a social media presence.
Bella:
Amazing. And for anyone in my community—the “Steak and Butter
Gang”—a lot of people already know you and love your content.
For those who are new, Bart is someone who speaks his mind very directly.
So I want to start with this: many people who follow a carnivore lifestyle are about 95–99% carnivore. They still have some carbs occasionally.
Could you explain why carbs might be problematic and give people that extra push to understand?
Bart:
Sure.
If someone is 95–98% carnivore compared to the standard Western diet, that’s already a win—no question about it.
And I’m not here to judge people who occasionally eat carbs. I’m human too. I’ve had carbs here and there.
But ideally, for the average person, it’s best to avoid them. And we’ll go into why—especially with something called the Randle cycle.
The key issue is that carbs tend to sneak up on people. They’re addictive. Many people struggle to moderate them.
So what starts as “just a little” can escalate quickly—two carbs here, then more, and before you know it, you’re consuming large amounts daily.
And that’s where the problem begins.
Bart (continued):
Carbs are appealing because, historically, they were rare. Our
bodies evolved to seek them out when they were available.
But now, we have constant access. Instead of occasional intake, people consume them multiple times a day, every day.
That creates metabolic issues involving glucose, fats, insulin, and inflammation.
So the short version is this: carbohydrates are not required in the human diet.
The exact requirement for dietary carbohydrates is zero.
Bart (continued):
A small amount may not harm you, but for many people, it
escalates. Once you cross your individual threshold, negative
effects begin.
One example is chronically elevated insulin.
When insulin stays elevated, it prevents your body from properly excreting sodium. That sodium is retained, which increases blood pressure over time.
Many people are told their high blood pressure has no known cause—but in many cases, it’s linked to elevated insulin from excessive carbohydrate intake.
High blood pressure contributes to cardiovascular disease and stresses the kidneys.
So again—if carbs aren’t necessary, why include them?
Bella:
I want to share my experience. I was vegan for six years, then
switched directly to carnivore—and I’ve been doing that for seven
years.
I’ve experienced both extremes, and I feel better than ever on carnivore. My health is amazing.
But people often say, “That’s extreme.” Or they ask, “Where are the long-term carnivores? Where’s the evidence?”
What would you say?
Bart:
There are examples.
There’s a rancher in Canada approaching 90 years old who has followed a carnivore diet for decades. Another individual has been carnivore for over 40 years.
So long-term examples do exist.
As for scientific evidence—this is where things get interesting.
There is no strong evidence for long-term health outcomes of any diet in humans. Nutrition science lacks the ability to establish true cause and effect.
Most studies are observational, not controlled. So in reality, all diets rely heavily on anecdotal evidence.
Bella:
Let’s go back to carbs.
Why do some people feel terrible when they eat them, while others seem fine?
Bart:
For people who have been strictly carnivore, their metabolism
adapts. They become efficient at running on fat and producing
glucose internally.
When they reintroduce carbs, they disrupt that system.
That can trigger immediate negative effects—partly due to the Randle cycle, and partly due to inflammation.
There’s also the possibility that some people transitioned incorrectly—too fast, without allowing proper adaptation.
They may then reintroduce carbs and feel better temporarily, but that’s often just a dopamine effect rather than a true improvement.
Bart:
Compared to the standard Western diet, even a small reduction in
carbohydrates is a win. There’s no two ways about it. And I’m not
here to judge anyone who has the occasional carb—I’m human myself,
and I’ve had carbs here and there.
What I say is this: ideally, for the average person, you should probably avoid carbs. We’ll talk about the reasons why, including the Randle cycle, which I’ll explain again shortly.
At the end of the day, if you’re consuming a significant amount of carbohydrates—and I don’t consider 5% significant, to be honest—they tend to sneak up on you. Carbs can become addictive. There’s a dependency aspect to them. Many people find it nearly impossible to moderate carbs effectively. For those individuals, the best approach is complete abstinence.
Because what happens is simple: you have a carb here and there, then that turns into two or three, then five, ten, twenty, and before you know it, you’re consuming large amounts daily.
If that’s how you want to live, that’s your choice—but that’s the reality of it.
Carbs are inherently appealing because, historically, they were rare. As a species, we evolved to seek them out because they were scarce. When we found them, it wasn’t a problem—our bodies could handle occasional intake.
But when you consume them multiple times a day, every day, you activate a metabolic problem. This involves interactions between glucose, fat, insulin, and broader physiological effects.
So the short version is this: carbohydrates are not a necessity in the human diet. The required amount of dietary carbohydrates is zero.
A small amount may not cause harm, but for most people, it escalates. Once you cross your individual threshold, negative effects begin. One example is chronically elevated insulin.
When insulin is elevated chronically, it prevents the body from excreting excess sodium efficiently. That sodium is retained, increasing blood volume and pressure—leading to higher blood pressure over time.
Many people are told their high blood pressure is “idiopathic,” meaning the cause is unknown. But in many cases, it’s linked to chronically elevated insulin from excessive carbohydrate intake.
High blood pressure contributes to cardiovascular disease and places stress on the kidneys. So again, carbs aren’t necessary—so why include them?
Bella:
I want to share something personal. I was vegan for six years,
then transitioned directly into a carnivore diet, which I’ve
followed for seven years now.
I’ve experienced both extremes—plant-based and animal-based—and I feel better than ever on carnivore. My health is excellent, and even things like my menstrual cycle improved significantly.
But people often say, “Isn’t that extreme?” They also question the lack of long-term evidence—like, where are the 90-year-old carnivores?
What would you say to that?
Bart:
First of all, there are examples. There’s a rancher in
Canada—Maggie—who is nearly 90 and has followed a carnivore diet
for decades. There are others as well—one individual has been
carnivore for over 40 years.
So yes, long-term anecdotal evidence does exist.
As for scientific evidence—this is where it gets interesting. There is no strong evidence for long-term health outcomes of any dietary pattern in humans. Nutrition science, as it stands, lacks the rigor required to establish causation.
Most studies are observational and rely on associations rather than controlled variables. So, in reality, we’re dealing with anecdotal evidence across all dietary approaches.
That levels the playing field.
Bella:
Let’s go back to carbs. Why is it that some people feel terrible
when they eat carbs, while others seem to tolerate them well?
Bart:
This is common among people who have been strictly carnivore for
some time. Their metabolism adapts—they become efficient at
running on fat and producing glucose internally through
gluconeogenesis.
When they reintroduce carbohydrates, they disrupt that system. This can trigger immediate negative effects, largely due to the Randle cycle and inflammatory responses.
There’s also the possibility that individuals who claim they “need carbs” didn’t transition properly. Switching diets abruptly can disrupt the microbiome and lead to delayed issues—sometimes months or even years later.
When those individuals reintroduce carbs, they may feel better temporarily. But often, that improvement is due to dopamine—not a true resolution of the underlying issue.
Bella:
Some people say, “Your body needs carbohydrates.” What do you say
to that?
Bart:
They’re partly correct. Certain tissues in the body do require
glucose. For example, if your blood glucose drops too low, that
can be life-threatening. There are tissues that either prefer or
require glucose to function.
However, what’s often misunderstood is this: your body can manufacture all the glucose it needs internally.
Through processes like gluconeogenesis, your body converts substances such as glycerol (from fats), lactate, and certain amino acids into glucose. So while glucose is necessary, dietary carbohydrates are not.
You do not need to consume a single gram of carbohydrates in your diet—ever.
Bella:
So if someone wants to try carnivore, what does a typical day of
eating look like?
Bart:
Keep it simple.
I aim for around 2 to 2.5 grams of protein per kilogram of ideal body weight—not actual weight if someone is overweight, but their target healthy weight.
To get that amount of protein, you’re typically eating about four times that amount in raw meat weight. The exact numbers aren’t critical long-term, but it gives you a rough guideline.
I eat meat and the fat that comes with it. If I’m hungrier—say I’ve been more active—I’ll add additional animal fat like butter.
After a while, this becomes intuitive. You don’t need to track or weigh everything. You just eat based on hunger.
Salt is optional—use it if you crave it. Water intake is simple: drink when you’re thirsty and stop when you’re not.
That’s it. Meat, animal fat, water, optional salt.
Bella:
Why is fat so important in this way of eating?
Bart:
There are two main reasons.
First, many essential nutrients are fat-soluble and are delivered through animal fat.
Second—and more importantly—fat is your primary energy source on this diet.
Protein is mainly used for building and maintaining body structures. It’s not primarily used for energy unless consumed in excess.
Fat is what gets oxidized to produce ATP—the energy currency of the body.
Your alternative energy source would be carbohydrates. But here’s the key point: mixing carbohydrates and fats together creates problems.
Bella:
Let’s get into that—what exactly is the Randle cycle?
Bart:
At its core, the Randle cycle describes what happens when both
fats and carbohydrates are competing to be used for energy at the
same time.
Both fuel sources ultimately get converted into the same intermediate molecule—acetyl-CoA—which feeds into the Krebs cycle (also called the TCA cycle). This is where energy production happens in the mitochondria.
Now imagine two large people trying to walk through a revolving door at the same time. The door jams. No one gets through efficiently.
That’s essentially what happens metabolically.
When both fuels are present in significant amounts:
- The energy system slows down
- ATP production becomes less efficient
- Inflammation increases
- Hunger signals go up
Even though there is plenty of energy available, the body struggles to use it properly.
This leads to chronic systemic inflammation, which is associated with conditions like cardiovascular disease, diabetes, autoimmune disorders, and more.
Bella:
So the issue is eating carbs and fat together?
Bart:
Exactly. That’s the worst-case scenario metabolically.
If you eat a diet high in carbohydrates and low in fat, you may initially see improvements—like weight loss—because you’re removing the metabolic conflict.
But that type of diet is often deficient in essential nutrients long-term.
On the other hand, a diet high in fat and low in carbohydrates provides all necessary nutrients and avoids this metabolic conflict.
Bella:
That’s a big claim.
Bart:
It’s based on the idea that humans evolved primarily consuming
animal-based foods over millions of years. From that perspective,
the body is well-adapted to that nutritional profile.
Bella:
So when people hear about the Randle cycle, they might think it’s
just a simple on/off switch. Is that accurate?
Bart:
No, not at all. It’s not binary—it operates along a spectrum.
Think of it more like a dimmer switch rather than a light switch. The degree to which the Randle cycle is active depends on how much fat and carbohydrate are present at the same time.
There’s also something else important here—metabolic inertia.
Imagine a train. It takes a lot of energy to get it moving, and once it’s moving, it takes a lot of energy to stop it or change direction.
Your metabolism behaves similarly. If your body is primarily burning fat, it prefers to continue doing so. If it’s burning carbohydrates, it tends to stay in that mode.
Switching between the two isn’t instantaneous—it takes time and energy.
Bella:
That makes sense. But people might say, “Okay, I won’t mix fats
and carbs—I’ll just eat carbs in the morning and fats later.”
Would that work?
Bart:
Not really.
Carbohydrates don’t just disappear immediately after you eat them. It can take around 72 hours for your body to fully clear them and transition into a fat-burning state.
So if you’re eating carbs in the morning and fat later in the day, you’re still overlapping those fuel sources. The Randle cycle is still active.
To truly switch between fuel systems, you’d need to allow enough time for one to fully clear before introducing the other—which is impractical for most people.
Bella:
So it’s not as simple as just separating meals.
Bart:
Correct. The overlap is the problem.
Also, remember that the Randle cycle contributes to what people call “insulin resistance.”
This is often misunderstood.
Insulin resistance is not necessarily a pathological condition—it can be a protective mechanism.
Bella:
That’s interesting. Can you explain that?
Bart:
Sure.
When your cells already have sufficient energy—especially from fat—they don’t need more glucose.
If glucose continues to enter the cells, it can cause damage through glycation, which is harmful.
So the body responds by reducing glucose uptake into cells. One way it does this is by removing GLUT4 transporters from the cell surface. These transporters normally allow glucose to enter the cell.
By pulling them away, the cell essentially says, “No more glucose—we’re full.”
That’s what we observe as insulin resistance.
But in this context, it’s not a malfunction—it’s the body protecting itself from excess energy and damage.
Bella:
So insulin resistance isn’t necessarily the cause of disease?
Bart:
Not in this framework. It’s a response to the conditions created
by mixing fuels—fat and carbohydrates together.
The problem arises when people continue consuming high amounts of carbohydrates while this protective mechanism is active. That leads to elevated blood glucose levels, which can contribute to damage over time.
Bella:
So the body is trying to maintain balance, but the diet is working
against it.
Bart:
Exactly.
Your body is always trying to maintain homeostasis. But if you constantly overload it with mixed fuel sources, it has to compensate in ways that may eventually lead to problems.
Bella:
People often talk about “metabolic flexibility”—the ability to
switch between burning carbs and fat. Is that something we should
be aiming for?
Bart:
In my view, that idea is largely marketing.
It sounds appealing—of course you’d want your metabolism to be flexible—but the reality is, you don’t need to consume carbohydrates at all. So there’s no real requirement to train your body to handle them.
Some people can tolerate carbs better than others, yes. But that doesn’t mean they’re necessary or beneficial.
For the average person, I would suggest focusing on a diet that aligns with human biology—primarily animal-based nutrition.
Bella:
That makes sense. But people often point out that many different
diets seem to work. For example, fruitarians sometimes look
healthy and vibrant—at least initially.
Bart:
That’s true—for a period of time.
Many diets can produce positive results in the short term. But the long-term outcomes are what matter.
With something like a fruit-based diet, you’re dealing with severe nutrient deficiencies—particularly protein and essential nutrients. Over time, that leads to noticeable decline: loss of muscle mass, poor skin quality, reduced energy, and other health issues.
The initial improvements people see are often due to removing processed foods or reducing calorie intake—not because the diet itself is nutritionally complete.
Bella:
What about people who eat carbs regularly but don’t seem to gain
weight or develop health problems?
Bart:
There’s variability between individuals. Genetics play a role, as
does lifestyle.
Some people can tolerate certain dietary patterns for longer without obvious consequences. But that doesn’t mean there are no effects happening beneath the surface.
Eventually, a diet that isn’t aligned with the body’s needs is likely to have an impact on healthspan and lifespan.
The challenge is that we don’t have long-term controlled studies to prove cause and effect in humans—so much of what we see is based on observation and inference.
Bella:
What about cholesterol—specifically LDL? There’s a lot of concern
about that.
Bart:
LDL is simply a transport mechanism. It carries lipids—like
cholesterol—through the bloodstream.
It exists because the body needs it. It’s produced according to the body’s requirements at any given time.
The idea that LDL is inherently harmful or the primary cause of heart disease is, in my view, incorrect.
Bella:
Another common claim is that carbohydrates help with things like
testosterone or reducing stress on the body. What do you think
about that?
Bart:
Those claims are largely opinion-based.
Just because an idea is widely repeated doesn’t make it true. There’s a lot of misinformation in nutrition, and people often accept claims without examining the underlying assumptions.
Bella:
Let’s wrap up with something practical. What’s the right way to start a
carnivore diet—and what’s the wrong way?
Bart:
The biggest mistake people make is switching overnight.
Going from a mixed diet straight into strict carnivore can cause problems—either immediately or delayed. It can disrupt the microbiome and create issues that might not show up for months.
Instead, transition gradually. Over several weeks:
- Reduce carbohydrates and plant foods
- Increase meat and animal fat
- Let your body adapt step by step
That’s a much smoother and safer approach.
Bella:
What are some other common mistakes?
Bart:
One major one is overconsuming liver.
There’s this idea that liver is a “superfood,” so people eat large amounts of it—fresh or in supplement form. That can actually cause imbalances.
A better approach is to consume liver in proportion to how it exists in an animal—which is a very small amount relative to muscle meat.
Bella:
What about meal frequency?
Bart:
You don’t need to force multiple meals a day.
Eat when you’re hungry. Over time, many people naturally reduce to fewer meals because the food is more satiating.
Bella:
What about people who say they lost too much weight on carnivore
and couldn’t maintain it?
Bart:
That’s likely an individual situation.
You’d need to look at:
- Whether they lost fat, muscle, or both
- Whether they were eating enough overall
- Their activity levels and metabolism
In most cases, if someone truly cannot maintain weight, it suggests they’re not consuming enough energy—but that requires a deeper, individualized look.
Bella:
So it’s not a one-size-fits-all answer.
Bart:
Exactly. There are general principles, but individual responses
vary.
Bella:
Final thoughts?
Bart:
Keep it simple.
Focus on:
- Meat and animal fat
- Eating according to hunger
- Avoiding unnecessary complexity
And most importantly—make changes gradually rather than all at once.