A recent University of Sydney study has been getting attention because it suggests older adults may improve biological-age markers in as little as four weeks through diet changes.

That is worth paying attention to.

I care about this subject personally. I changed the way I eat. I cut out seed oils and ultra-processed foods. I lowered carbohydrates. I focused on grassfed beef, eggs, salads, broth, and real food. Then I shared my own bloodwork publicly because I think people deserve to see real examples, not just theories.

[Link to my bloodwork post here]

My results do not prove what everyone else should do. I am not a doctor, and I am not giving medical advice. But my experience is enough to make me ask a simple question:

Why is a true ketogenic diet so often left out of these studies?

The Study Was Interesting, But It Did Not Test Keto

The University of Sydney study looked at 104 adults between the ages of 65 and 75. They were assigned to one of four diets for four weeks. The researchers then measured changes in biological-age markers using blood pressure and blood markers such as cholesterol, insulin, and C-reactive protein.

The four diets were:

• Omnivorous high-fat
• Omnivorous high-carbohydrate
• Semi-vegetarian high-fat
• Semi-vegetarian high-carbohydrate

All four diets had the same protein level: 14% of calories from protein.

The group that did best, according to the University of Sydney summary, was the omnivorous high-carbohydrate group. That group ate 14% protein, 28–29% fat, and 53% carbohydrate.

The group that showed no meaningful change was the omnivorous high-fat group. The public summary says that group’s diet most closely resembled the participants’ baseline diets.

That detail matters.

This was not a test of keto.

It was a test of several mixed diets, including one labeled “high-fat” that still contained a large amount of carbohydrate.

Keto Is Not Just “High Fat”

This is where the public conversation often gets sloppy.

Keto is not simply eating more fat.

A true ketogenic diet is a carbohydrate-restricted diet designed to change the body’s fuel system. For many people, that means reducing carbohydrates to somewhere around 15–50 grams per day, depending on the person, their activity level, and their metabolic health.

You do not get there by eating a diet that is still more than 40% carbohydrate.

That is the problem with calling a diet “high-fat” and then letting people assume it tells us something about keto.

A person can eat more fat and still not be in ketosis. A person can eat somewhat fewer carbohydrates and still not be in ketosis. There is a real threshold involved. You either lower carbohydrates enough to make ketones a meaningful fuel source, or you do not.

That does not mean the body uses only one fuel at a time. Biology is more complicated than that. Even in ketosis, the body still uses some glucose. Even on a high-carbohydrate diet, the body still burns some fat.

But the metabolic state is different.

That is the point.

A diet that is high in fat while still high in carbohydrate is not the same thing as a low-carbohydrate ketogenic diet.

My Concern Is the Advice Attached to the Study

The study itself is useful.

It shows that older adults can respond quickly to diet changes. The researchers were also careful to say this is preliminary and that longer-term trials are needed to know whether these changes last or reduce disease risk.

That is reasonable.

My concern is what often happens after the study gets translated into public advice.

The article I read about this study listed “limit saturated fat” as the first practical recommendation.

But I do not see where this study isolated saturated fat as the cause of anything.

The study compared broader dietary patterns. It compared higher fat versus lower fat. It compared higher carbohydrate versus lower carbohydrate. It compared omnivorous diets with semi-vegetarian diets. It did not appear to test saturated fat by itself as an independent variable.

That is an important difference.

If a study does not isolate saturated fat, I do not think the public advice should make saturated fat the main villain.

This is where nutrition reporting often loses me. A study tests one thing, but the advice turns into something more familiar:

Eat less animal fat.
Eat more plants.
Eat more complex carbohydrates.
Limit saturated fat.

Maybe that advice helps some people, especially compared with a modern diet built around ultra-processed food.

But that is not the same as proving saturated fat caused the worse result in this study.

The Missing Question

The better question is not simply:

Is fat good or bad?

The better question is:

What happens when people remove ultra-processed food, remove seed oils, lower carbohydrates enough to enter a ketogenic state, and eat real food with adequate protein?

That is the question I wish more researchers would ask directly.

Because that is what many people are actually doing.

They are not just adding butter to a high-carbohydrate diet. They are not eating a normal processed diet with extra fat poured on top. They are removing bread, pasta, sugar, seed oils, packaged snacks, and most ultra-processed foods. They are eating meat, eggs, leafy greens, broth, butter, and other real foods.

That is a different diet.

It deserves to be studied as its own thing.

High Fat With High Carbohydrate Is a Different Diet

I think this is the part many people miss.

A high-fat diet with high carbohydrates is not keto.

It may be common. It may look like a lot of modern eating. But it is not the same metabolic state as ketosis.

This matters because the body handles nutrients in context.

If carbohydrate intake stays high, insulin stays involved in managing that glucose load. If fat intake is also high, then the body is being asked to manage both fuels at the same time.

That is not the same thing as reducing carbohydrates low enough for the body to rely more heavily on fat and ketones.

So when a study tests high fat in the presence of substantial carbohydrate, it should not be used to dismiss a true ketogenic diet.

The study may tell us something about a higher-fat mixed diet.

It does not tell us what would happen with a well-formulated low-carbohydrate ketogenic diet.

This Matters for Older Adults

This study focused on adults age 65 to 75.

That is one reason I paid attention.

As people get older, many are thinking seriously about glucose, insulin, inflammation, muscle, body composition, energy, and long-term health. I am one of them.

I have had my own reasons to think carefully about glucose every time I eat. That is part of why I changed my diet in the first place.

For me, lowering carbohydrates was not a diet trend. It was a practical decision. I wanted better bloodwork. I wanted better health markers. I wanted to stop eating the foods that had become normal in the industrial food system.

That meant removing seed oils and ultra-processed foods completely.

It also meant paying attention to the source of my food.

For me, grassfed beef is not just “protein.” It comes from a farming system. Soil grows forage. Forage feeds cattle. Cattle become food. The health of that whole chain matters.

That is why I think a real-food ketogenic diet should not be lumped in with a high-fat mixed diet.

They are not the same thing.

Protein Also Deserves More Attention

Another detail in this study matters to me.

All four diet groups had protein set at 14% of calories.

For older adults, I think that raises a fair question.

Many people over 60 are trying to preserve muscle. They are thinking about strength, independence, falls, bone health, and the ability to keep moving. Protein matters in that conversation.

So when I see a study about older adults where protein is held at 14% across all groups, I want to be careful about applying the results too broadly.

A real-world low-carbohydrate diet for someone focused on health, strength, and aging may include more protein than that. It may include grassfed beef, eggs, chicken, fish, dairy, and other nutrient-dense foods.

Again, that is a different question than the one this study tested.

What I Wish the Study Had Included

I would like to see a study with a true low-carbohydrate ketogenic group.

Not a “high-fat” group with 40% carbohydrate.

A real ketogenic group.

Something like:

• Carbohydrates low enough to produce nutritional ketosis
• Adequate protein, especially for older adults
• No seed oils
• No ultra-processed foods
• Whole-food animal proteins
• Leafy vegetables and low-carbohydrate plants
• Measurements of glucose, insulin, triglycerides, HDL, CRP, body composition, ApoB, LDL particle markers, and ketones

That would be a more honest test.

Then we could compare metabolic states instead of comparing broad diet labels.

Because “high fat” is not a metabolic state.

Ketosis is.

I Am Not Asking Everyone to Eat Like Me

I am not saying every person needs to eat exactly the way I do.

Some people may do well with more carbohydrates, especially from whole foods. Some people may do well with legumes, fruit, or intact grains. People are different.

But I do think this matters:

If we are going to talk about keto, then test keto.

If we are going to warn people about saturated fat, then show that saturated fat was actually the variable being tested.

If we are going to talk about healthy aging, then do not leave out one of the most serious questions many people are already asking:

What happens when an older adult removes ultra-processed foods, removes seed oils, lowers carbohydrates enough to enter ketosis, and eats real food from animals raised on pasture?

That is the study I want to see.

The Bottom Line

The University of Sydney study may tell us something useful.

It suggests older adults can change biological-age markers in a short period of time through diet. That is encouraging.

But it does not answer the keto question.

It did not test a true low-carbohydrate ketogenic diet. It did not isolate saturated fat as the cause of worse outcomes. And it should not be used to steer people away from animal fats as if that conclusion was directly proven.

My concern is not that the study failed to defend keto.

My concern is that keto was avoided again.

And then the public advice still came back to the same place: limit saturated fat.

For people like me, who have changed our health by removing seed oils, removing ultra-processed foods, lowering carbohydrates, and eating real food, that is not a small detail.

It is the central question.

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FAQ Section

Did the University of Sydney biological age study test keto?

No. The study tested four diet patterns, including higher-fat and higher-carbohydrate diets, but the “high-fat” diets still contained enough carbohydrate that they should not be described as ketogenic.

What is the difference between high-fat and keto?

High-fat describes the amount of fat in the diet. Keto describes a metabolic state where carbohydrate intake is low enough for the body to produce and use ketones as a meaningful fuel source.

How many carbs does it take to get into ketosis?

It varies by person, but many people need to reduce carbohydrates to roughly 15–50 grams per day to enter nutritional ketosis. A diet with more than 40% of calories from carbohydrates is not keto in any practical sense.

Did the study prove saturated fat is bad for biological aging?

No. The study compared broader dietary patterns. It did not appear to isolate saturated fat as the independent variable. Advice to limit saturated fat may reflect broader nutrition assumptions, but it should not be presented as the direct finding of this study.

Why does this matter for people eating low carb?

It matters because a low-carbohydrate ketogenic diet is metabolically different from a mixed diet that contains both high fat and high carbohydrate. Studies that test high-fat mixed diets should not be used to make claims about keto.

Can a person eat grassfed beef on a ketogenic diet?

Yes. Grassfed beef can fit into a ketogenic diet because it is naturally low in carbohydrates and provides protein, fat, iron, zinc, B vitamins, and other nutrients. The full diet still needs to be built carefully around a person’s health needs.

Is this medical advice?

No. This is my personal interpretation of the study and my own experience. Anyone making major diet changes, especially with medications or medical conditions, should work with a qualified clinician.

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