When it comes to weight loss, the scale is famously easy to fool. Both the Keto and Mediterranean diets promise fast results, but what happens under the bonnet of your cardiovascular system tells a very different story.
Before you cut carbohydrates or double down on saturated fats, South African cardiologists and dietitians warn that shedding kilograms means little if you are damaging your arteries in the process.
By putting these two popular approaches head-to-head, we can uncover how they truly stack up nutritionally, expose the marketing traps of the wellness industry, and understand what they mean for long-term heart health - backed by insights from a recent Wits University study on nutrition and metabolism.
"Changing gears" vs refining the fuel
When assessing how the Keto and Mediterranean diets alter the cardiovascular system, look past the weight scale.
As Leane Kiezer, registered dietitian and head of public affairs at Danone Southern Africa, points out: “The truth is that any diet that creates a sustained energy deficit can result in weight loss ... But what happens to your health beyond the number on the scale can look very different too.”
Kiezer uses a vehicle analogy to explain what occurs under the bonnet of the human body, summing them up as below:
The Keto diet: "By drastically eliminating carbohydrates, the body burns through its stored glycogen. Because glycogen is stored alongside water, the scale drops quickly early on, akin to squeezing water out of a sponge.
"The liver then converts fat into ketones, shifting the car into a completely different gear to run the brain and tissues on fat-derived fuel."
The Mediterranean diet: "Rather than forcing a metabolic gear shift through severe restriction, this approach focuses entirely on the quality of what goes into the tank.
"It builds volume and satiety using fibre-rich whole grains, legumes, fruits, vegetables, lean proteins, and unsaturated fats, allowing individuals to naturally consume fewer kilojoules while keeping the metabolic engine running smoothly."
Demystifying the low-carb alphabet soup
In South Africa, the low-carb movement is highly commercialised, often blurring the lines between different regimens.
However, they are not interchangeable, according to Keizer:
- Keto: Designed to keep carbohydrate intake strictly between 20–50 grams a day to induce deep ketosis.
- Atkins: Starts with ultra-low carbs but features a phased approach where carbohydrates are gradually reintroduced over time.
- Banting: As commonly followed in South Africa, it is a low-carbohydrate, higher-fat approach, though individual food choices vary wildly.
- Keto 800: Extends the restriction by combining very low carbohydrate intake with an extreme, crash-diet energy limit of around 800 calories (approx. 3,350 kJ) a day.
“For cardiovascular health, the specific diet label matters far less than what is actually on the plate. Two people can both say they are 'doing keto' and eat opposite nutritional profiles.
"One might build meals around butter, cream, bacon, and processed meats, while another uses avocado, nuts, seeds, spinach, cabbage, broccoli, fish, and predominantly unsaturated fats. Same label, vastly different cardiac outcomes,” Keizer explains.
Inside the artery: The anatomy of a vulnerable plaque
To truly grasp why your food choices matter, we must look directly at the cellular landscape of the blood vessels.
According to Associate Professor Naylin Bissessor, a consultant interventional cardiologist with a specialised interest in advanced intracoronary imaging, the architectural stability of an arterial plaque dictates your heart attack risk.
“High LDL cholesterol can contribute to fatty deposits in artery walls. Over time, these deposits may become unstable and trigger a heart attack. That is why weight loss alone is not enough: cholesterol, blood pressure, blood sugar, smoking and family history also matter,” explains Bissessor.
The biological chain reaction
“Heart attacks often develop over time as cholesterol and inflammation damage the lining of the arteries,” says Bissessor.
“LDL cholesterol can enter the artery wall and contribute to fatty deposits. Some deposits become fragile and may rupture, causing a blood clot that blocks blood flow to the heart. Risk factors include smoking, high blood pressure, diabetes, and fat stored around the internal organs.”
The metabolic trade-off
“Relying strictly on the scale is highly dangerous because improving one metabolic marker on keto frequently comes at the direct expense of another,” adds Bissessor.
Data from clinical trials show that while both diets can successfully achieve weight loss and improvements in blood glucose, the cardiovascular profiles diverge dramatically:
- LDL cholesterol: Higher on keto than the Mediterranean diet. Saturated fats raise LDL, which plays a direct, causal role in the build-up of plaque over time.
- Triglycerides: Drop more significantly on a keto diet due to severe carbohydrate restriction.
- Blood pressure and inflammation: Both markers show consistently better, lower profiles on the Mediterranean diet. Inflammation remains high on standard keto diets due to the high saturated fat intake.
“A keto diet may improve blood sugar while also raising LDL cholesterol, depending on the foods chosen. People with diabetes, high cholesterol, or a high risk of heart disease should therefore seek medical advice before using keto to manage blood sugar,” he cautions.
Protein is not automatically healthy
“Protein is important, particularly for people who exercise, but eating more than the body needs does not necessarily build more muscle or improve health," says Kiezer. "The whole food matters: a diet built around bacon, fatty red meat, processed meats and boerewors may also be high in saturated fat and salt, while leaving less room for vegetables, beans, lentils, nuts and seeds.”
Being fit does not remove the risks associated with high LDL cholesterol or a family history of heart disease, Bissessor says.
“People who exercise regularly should still monitor their cholesterol and consider the quality of the foods providing their protein,” Bissessor notes.
The best diet depends on your health history, lifestyle and goals. For people with diabetes, high cholesterol or cardiovascular disease, weight loss should not be the only aim; protecting the heart over the long term matters too, says Kiezer.
If you reduce carbohydrates, what replaces them is important.
Kiezer recommends choosing unsaturated fats and fibre-rich plant foods rather than replacing carbohydrates with butter, fatty meat or highly processed foods, and explains, "Before adopting any extreme dietary shift, patients must ask themselves a vital clinical question: Can I eat this way forever?"
An affordable South African Mediterranean pattern
The Mediterranean diet is a flexible eating pattern, not an expensive menu. It emphasises vegetables, fruit, beans, lentils, whole grains, fish, nuts and unsaturated oils, and is supported by evidence for cardiovascular health.
Affordable local choices include:
- Breakfast: Oats with plain yoghurt or maas, plus seasonal fruit.
- Lunch: Wholewheat toast with pilchards, sardines or avocado.
- Snacks: Fruit and a handful of peanuts.
- Dinner: Samp and beans, lentil curry, skinless chicken with vegetables, or pap with morogo, beans or chakalaka.* Cooking oil: Canola oil is an affordable alternative to olive oil.
Kiezer’s advice is to “add before you subtract”.
"Add vegetables, beans, lentils, fruit, yoghurt and fish before focusing on removing foods.
“By gradually making these nourishing whole foods the foundation of your daily routine, you can step off the wellness industry’s volatile trend cycle and give your heart the long-term protection it deserves.”
vuyile.madwantsi@nationalmg.co.za