Mediterranean vs Keto: A Cardiologist Compares Heart Health, Cholesterol, and Long-Term Safety

As America's Cardiologist, I've spent my career studying how nutrition, cholesterol, and lifestyle choices impact heart disease, the number one cause of death worldwide. I spend countless hours a day educating patient online.

And the question I get more than almost any other is this one: "Dr. Alo, should I do keto or Mediterranean?"

Both diets have passionate fans. Both can help you lose weight. But your heart doesn't care how fast the scale moves this month. It cares about your LDL cholesterol, your blood pressure, your blood sugar and what happens to your arteries over the next 20 years. So let's compare them the way a cardiologist would, with the actual trials, and the key charts redrawn so they're easy to read.

Medical note: This article is for general education and is not a substitute for advice from your own doctor. If you take medication for diabetes or blood pressure, talk to your doctor before making a major change to your diet.

Heart Healthiest Diet Infographic Summary:

Key takeaways

• The Mediterranean diet has cut heart attacks, strokes and cardiovascular deaths in randomized trials: 31% fewer events with extra-virgin olive oil in PREDIMED, and 25% fewer in people who already had heart disease in CORDIOPREV. No randomized trial has shown that keto does this.
• In a Stanford trial where the same people ate both diets, LDL went up 10% on keto and down 5% on Mediterranean. Keto lowered triglycerides more.
• Blood sugar (A1c) improved the same on both diets, and weight loss was about the same.
• Over a year, healthy low-carb and healthy low-fat diets produced nearly identical weight loss. Weight loss comes down to calories.
• If you love low-carb, do a Mediterranean-style low-carb: olive oil, nuts, fish and avocado, with saturated fat kept low.

What Is The Best Heart Healthy Diet?

The best heart healthy diet is one that lowers the things that cause heart disease, especially LDL cholesterol and blood pressure, and that has actually been shown to prevent heart attacks and strokes in people. That second part matters. Plenty of diets improve a lab number for a few weeks. Very few have been tested against heart attacks and deaths.

What Is the Mediterranean Diet?

The Mediterranean diet is a plant-forward way of eating built around vegetables, fruits, legumes, whole grains, nuts and extra-virgin olive oil, with fish and poultry several times a week and very little red meat, processed meat, butter or sweets. The DASH diet is a close cousin: the same foundation, with salt kept low.

It's high in fiber and unsaturated fats and low in saturated fat. That combination is exactly what lowers LDL cholesterol.

Why Cardiologists Favor the Mediterranean Diet

Figure: percent fewer major cardiovascular events with a Mediterranean diet in randomized trials. Redrawn from Estruch R, et al. N Engl J Med. 2018; Delgado-Lista J, et al. Lancet. 2022; de Lorgeril M, et al. Circulation. 1999 (Results).

Because it has been tested where it counts. Here's how to read the chart:

• The top two bars are PREDIMED, a Spanish trial of 7,447 people at high risk who didn't have heart disease yet. Compared with a reduced-fat diet, a Mediterranean diet with extra-virgin olive oil cut heart attacks, strokes and cardiovascular deaths by 31%. With nuts, by 28%.
• The bottom bar is CORDIOPREV, a trial of 1,002 people who already had coronary heart disease. Over about 7 years, a Mediterranean diet cut further events by about 25% compared with a low-fat diet.
• The note at the bottom is the Lyon Diet Heart Study. After a first heart attack, people assigned to a Mediterranean diet had 14 cardiac deaths or heart attacks, compared with 44 in the group eating a Western-style diet.

Three randomized trials, in people with and without heart disease, all pointing the same way. Keto has none.

What Is the Keto Diet?

A ketogenic diet cuts carbohydrates so low, usually under about 20 to 50 grams a day, that your body switches to burning fat and making ketones for fuel. A typical keto diet is about 70% to 80% fat, 10% to 20% protein and 5% to 10% carbohydrates.

That means no bread, rice, pasta, potatoes or sugar, but also very little fruit, beans, lentils or whole grains. In practice, many people fill that gap with butter, cheese, cream, bacon and red meat. That's where the trouble starts for your heart.

Mediterranean vs Keto: Heart Health Comparison

Figure: the cardiologist's scorecard. Results from Gardner CD, et al. Am J Clin Nutr. 2022 (Keto-Med) and JAMA. 2018 (DIETFITS); outcome trials as above.

How to Interpret the Cardiologist Diet Comparison Graphic

Each row is something that matters for your heart. The last column tells you which diet came out ahead, based on randomized trials.

• Keto wins one row: triglycerides. Cutting carbs lowers them.
• Two rows are a tie: weight loss and blood sugar. Both diets work when you eat less.
• Mediterranean wins the rest: LDL cholesterol, fiber and nutrients, how easy it is to stick with, and the one row that matters most, fewer heart attacks and strokes in real trials.

Weight Loss

Figure: average weight lost after 12 months. Redrawn from Gardner CD, et al. JAMA. 2018 (DIETFITS, Results).

In the DIETFITS trial, 609 adults were randomly assigned to a healthy low-fat or a healthy low-carb diet for a year. Both groups were coached to eat whole foods and avoid sugar and refined grains.

• The low-fat group lost 5.3 kg (about 12 pounds). The low-carb group lost 6.0 kg (about 13 pounds).
• The difference, 0.7 kg, wasn't statistically significant. Neither their genes nor their insulin levels predicted which diet would work better for them.

A meta-analysis of 11 trials found low-carb diets lost about 2 kg more than low-fat diets on average, but raised LDL cholesterol at the same time.

Keto often looks faster in the first weeks because cutting carbs drops water weight. Over the long run, weight loss comes down to calories. You can lose weight on almost any diet if you eat less than you burn. The question is which diet protects your heart while you do it, and which one you can actually keep up.

Cholesterol and LDL

Figure: percent change after 12 weeks on each diet. Redrawn from Gardner CD, et al. Am J Clin Nutr. 2022 (Keto-Med, Results).

This is the most important chart in this article. In the Keto-Med trial at Stanford, adults with prediabetes or type 2 diabetes ate a well-formulated keto diet for 12 weeks and a Mediterranean diet for 12 weeks, in random order. Same people, both diets.

• LDL cholesterol went up 10% on keto and down 5% on Mediterranean. That's a 15-point swing in the wrong direction, and LDL is the cholesterol that builds plaque.
• Triglycerides fell more on keto (16% vs 5%), and HDL rose more (11% vs 7%).
• Weight loss was similar (8% vs 7%), and A1c improved on both diets with no difference between them.

And this was a well-formulated, whole-food keto diet designed by researchers. A keto diet built on bacon, butter and cheese can raise LDL far more, because saturated fat is what drives LDL up, and in some people the rise is dramatic.

Higher HDL and lower triglycerides look nice on a lab report, but they don't cancel out a higher LDL. LDL and apoB are the numbers that cause plaque.

Inflammation and Blood Vessel Health

The Mediterranean diet is rich in fiber, polyphenols from olive oil, fruit and vegetables, and omega-3 fats from fish and nuts. Studies of Mediterranean eating patterns have shown improvements in markers of inflammation and in how well blood vessels relax.

Keto's effect on inflammation depends heavily on what you eat. A keto diet built on olive oil, nuts, fish and avocado is a very different diet from one built on bacon and butter. The saturated-fat version raises LDL, which is the main driver of inflammation inside the artery wall, where plaque grows.

Nutrient Quality and Food Variety

To stay in ketosis, you have to cut most fruit, beans, lentils, chickpeas and whole grains. Those are some of the most heart-protective foods we have, and they are where most of our fiber comes from. In the Keto-Med trial, people ate less fiber and lower amounts of 3 other nutrients on keto than on the Mediterranean diet.

Fiber lowers LDL cholesterol, helps control blood sugar and keeps you full. It's one of my top heart habits for a reason.

Long-Term Safety and Sustainability

The Mediterranean diet has decades of data, including randomized trials lasting 4 to 7 years with heart attacks, strokes and deaths as the outcome. Keto trials usually last weeks to months and measure lab numbers, not heart attacks.

Sustainability matters too. In the Keto-Med trial, 12 weeks of follow-up after the study diets ended suggested the Mediterranean diet was easier to keep up. A diet you abandon after three months doesn't protect your heart for the next 20 years.

Cardiologist's Verdict

For the vast majority of my patients, the Mediterranean diet is the foundation for heart protection. It lowers LDL, it has been proven to prevent heart attacks and strokes, and people can stay on it for life.

If you love low-carb eating, you don't have to give it up. Do a Mediterranean-style low-carb diet: build it on olive oil, nuts, avocado, fish and non-starchy vegetables, keep saturated fat low, and check your LDL or apoB a few weeks after you start. If it goes up, change course.

Who Should Be Careful With Keto

• Anyone with heart disease, high LDL or a high apoB. If you've had a heart attack, stent or stroke, or your LDL is already high, a saturated-fat-heavy keto or carnivore diet can push it higher. Please talk to your cardiologist first.
• People with familial hypercholesterolemia or high Lp(a). Your risk is already high from birth, and you can't afford an LDL increase.
• People taking insulin or sulfonylureas for diabetes, because blood sugar can drop dangerously low, and people taking SGLT2 inhibitors (like empagliflozin or dapagliflozin), because very low-carb diets raise the risk of a serious condition called ketoacidosis. Your doctor needs to adjust your medications.
• People with kidney disease, women who are pregnant or breastfeeding, and anyone with a history of an eating disorder.

The fine print

• Keto-Med was small and short: 33 people with complete data, 12 weeks on each diet. The weight and HDL results depended partly on which diet people did first. But the LDL and triglyceride results were clear.
• PREDIMED was retracted and republished in 2018 after problems with how some participants were randomized. The corrected analysis, which accounted for those problems, found the same benefit.
• In CORDIOPREV, the benefit was clear in men, who made up about 83% of participants. No difference was found in the 175 women, a group too small to be sure either way.
• No trial has directly compared keto and Mediterranean diets on heart attacks. The case for Mediterranean rests on its own outcome trials and on the LDL difference, which we know drives heart disease.

The myth: "Keto is better for your heart because it raises HDL"

Raising HDL with drugs has failed to prevent heart attacks in large trials. HDL is a marker, not a target. LDL and apoB cause plaque, and keto usually pushes them the wrong way. A lab report that shows higher HDL and lower triglycerides alongside a higher LDL is not a healthier heart.

What I tell my patients

1. Reduce saturated fat, increase fiber, and take your medications if you need them. These move the needle most.
2. Make the Mediterranean or DASH pattern your base: vegetables, fruit, legumes, whole grains, nuts, olive oil and fish.
3. Lose weight with a calorie deficit you can keep. The diet you'll stick with beats the "perfect" diet you'll quit.
4. If you go low-carb, make it Mediterranean-style and check your LDL or apoB within a couple of months.
5. Then: do cardio, lift weights, reduce stress and improve sleep. And don't smoke.

Frequently asked questions

Which is better for heart health, keto or Mediterranean?
Mediterranean. It lowers LDL cholesterol and has been shown in randomized trials to cut heart attacks, strokes and cardiovascular deaths. Keto usually raises LDL and has no outcome trials.

Which diet is better for weight loss?
Over a year, they work about the same. In the DIETFITS trial, healthy low-carb and healthy low-fat diets produced nearly identical weight loss. Pick the one you can maintain.

Does keto raise cholesterol?
Usually, yes. In the Keto-Med trial, LDL went up 10% on a well-formulated keto diet. Diets high in saturated fat often raise it much more.

Is keto good for diabetes?
Keto can lower blood sugar, but in the Keto-Med trial a Mediterranean diet improved A1c just as much without raising LDL. For type 2 diabetes, the calorie deficit and weight loss do most of the work.

Can I do a low-carb Mediterranean diet?
Yes. Focus on olive oil, nuts, avocado, fish, eggs in moderation and non-starchy vegetables, and keep saturated fat low. Check your LDL after a few weeks.

Final Thoughts On the Healthiest Cardiology Diet?

Keto can help you lose weight and lower your triglycerides. But so can a Mediterranean diet, without pushing up the LDL cholesterol that builds plaque, and with decades of trials showing fewer heart attacks, strokes and deaths. For protecting your heart over the next 20 years, not just the next 20 pounds, the Mediterranean diet is the clear winner.

Related Food & Diet Posts

Explore in-depth evidence on nutrition, dietary approaches, and cardiovascular health:

• Dr. Alo's Dietary Guidelines – The complete framework
• Mediterranean Diet: The Evidence – Research behind the winner
• Is The Carnivore Diet Safe? – All-meat diet safety
• Is Saturated Fat Bad For Your Heart? – The fat quality issue
• Red Meat Healthy? Latest Science – Protein and health
• Are Seed Oils Bad For You? – Oil quality matters
• Is Fish Oil Really Good For Your Heart? – Supplement evidence
• Are Eggs Healthy? – Cholesterol food myths
• Science Says It's OK To Eat Carbs! – Carbohydrate myths
• 7 Reasons You Shouldn't Do Intermittent Fasting – Eating pattern problems
• Does Sugar Cause Heart Disease? – Sugar nuance
• Is Coffee Really Good For You? – Beverage evidence
• The Dangers of Diet Culture – Diet culture criticism
• You Can't Outrun Your Diet – Exercise vs nutrition

Still have questions? Stop Googling and ask Dr. Alo.

You've read the science, but applying it to your own life can be confusing. That's exactly what the Heart 2 Heart VIP Community is for. You can ask me questions directly, join live video calls where we talk through your labs and situations like this one, and get physician-level guidance based on your actual numbers.

Join here: https://dralo.net/community 💪🏻🩺🫀

Dr. Alo

References

1. Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. New England Journal of Medicine. 2018;378(25):e34. doi:10.1056/NEJMoa1800389.
2. Delgado-Lista J, Alcala-Diaz JF, Torres-Peña JD, et al. Long-term secondary prevention of cardiovascular disease with a Mediterranean diet and a low-fat diet (CORDIOPREV): a randomised controlled trial. Lancet. 2022;399(10338):1876-1885. doi:10.1016/S0140-6736(22)00122-2.
3. de Lorgeril M, Salen P, Martin JL, et al. Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study. Circulation. 1999;99(6):779-785. doi:10.1161/01.CIR.99.6.779.
4. Gardner CD, Landry MJ, Perelman D, et al. Effect of a ketogenic diet versus Mediterranean diet on glycated hemoglobin in individuals with prediabetes and type 2 diabetes mellitus: the interventional Keto-Med randomized crossover trial. American Journal of Clinical Nutrition. 2022;116(3):640-652. doi:10.1093/ajcn/nqac154.
5. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. JAMA. 2018;319(7):667-679. doi:10.1001/jama.2018.0245.
6. Mansoor N, Vinknes KJ, Veierød MB, Retterstøl K. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. British Journal of Nutrition. 2016;115(3):466-479. doi:10.1017/S0007114515004699.