The three worst diets for heart health

1. The carnivore diet

The carnivore diet involves restricting your food to animal sources and eliminating healthy plant foods and carbohydrates. Which means meat, fish, eggs and some dairy, like butter and cream, are on the menu, making the diet high in protein and saturated fat, and low in fibre.

Yet the evidence is clear that saturated fat, particularly from fatty red meat and unfermented dairy, can lead to a rise in LDL, understood as “bad” cholesterol. “In the short term, you might lose weight, but over the long term, your bad cholesterol can become high and we know that can lead to furring of the blood vessels, which can ultimately lead to strokes, heart attacks and kidney problems,” says Dr Guttmann.

Processed red meat, such as sausages and bacon, also contains very high levels of salt, which is one of the leading drivers of high blood pressure. In the UK, consumers are already consuming 40% more sodium (8.4g per day) than the recommended maximum daily intake level of 6g per day.

“Excessive salt narrows the blood vessels and slows blood flow to your organs, and that’s why it’s really important to always monitor how much salt you consume,” says Dr Guttmann.

The other issue is that this diet also cuts out foods that actively protect our hearts. “The carnivore diet worries me most for what it excludes,” says Tracy Parker, senior dietitian at the British Heart Foundation. “You’re eliminating wholegrains, fruit, vegetables, pulses. That’s a loss of fibre and antioxidants that help protect our blood vessels.”

She explains: “High blood pressure and high cholesterol damage the artery wall. The body’s inflammatory response kicks in, and over time, you get atherosclerosis – the fatty plaques that raise heart attack and stroke risk. Plant foods supply fibre and antioxidants that help dampen that process.”

2. The keto diet

The keto diet began life in the 1920s when it was discovered that it could reduce seizures in children with epilepsy. Nowadays, it’s mostly used as a weight loss tool. It’s a very low-carb diet, with around 20-50g of carbohydrates allowed per day. When the body has no carbohydrates (glucose) to use for energy, it turns to fat as its energy source, releasing ketones, hence the name.

In practice, like the carnivore diet, most calories come from fat, with meat, fish, eggs, cheese, butter, oils, and nuts featuring heavily, with limited amounts of non-starchy vegetables also allowed.

Given the high fat content, it carries many of the same heart risks as the carnivore diet, with high saturated fat and low fibre increasing bad cholesterol in the body. Although the fibre content is slightly higher, most versions still fall well short of fibre needs, and it also restricts heart-healthy polyphenols usually found in plant foods.

Sarah Berry, professor of nutritional sciences at King’s College London, says: “Ninety-five per cent of the UK doesn’t get enough fibre, and on strict keto, you definitely won’t get adequate fibre. Fibre reduces bad cholesterol, but also plays an important role in metabolism, and provides amazing food for our gut bacteria, which we know is linked to a healthy heart.

“On keto, you’ll also miss out on plant bioactives, such as polyphenols, which are really critical for heart health. We know that a lot of cardiovascular disease is underpinned by chronic low-grade inflammation, and polyphenols can dampen that reaction down.”

To make the diet healthier, take a more moderate low-carb approach and include some wholegrains, pulses, nuts and seeds, and focus on unsaturated fats like olive oil, nuts, seeds and oily fish and limit red and processed meats.

“Low-carb diets of around 130g per day have been shown to be safe and effective for people with Type 2 diabetes,” says Tracy Parker.

3. Intermittent fasting

There’s been some scary headlines recently linking intermittent fasting and cardiovascular mortality, yet the new studies are observational and don’t yet prove cause and effect.

Experts suggest that if 16:8 intermittent fasting does have a negative effect, it may be more to do with what and when you eat, rather than the eating window itself. Extreme fasting regimes can also be damaging.

In his clinics, Guttmann has seen that fasting often leads his patients to overeat the wrong foods. “People skip food all day, then come home starving and overeat ultra-processed, salty foods because they’re so hungry, so they’re gaining weight and not getting the right nutrition,” he says.

The timing of when we eat also matters. Filling up late at night can disrupt our body’s ability to process food, which can raise our blood sugar and ultimately impact our heart. “We know that eating later in the day is not as good for our metabolic health as eating earlier,” says Berry.

Guttmann emphasises that intermittent fasting isn’t suitable for everyone. “It’s not suitable for people with diabetes as they struggle to control their blood sugar, or the elderly as they can be prone to dehydration, or for pregnant women. And if your window is so narrow you can’t meet your nutrient needs, it’s not helping your heart.”

So what is the best diet for heart health?

First of all, the good news: changes to our diets can make a difference to our heart health fairly quickly.

In his clinic, Guttmann reports that within two to three months of healthier eating, he will see measurable differences in patients’ cholesterol, blood sugar and blood pressure. Cholesterol can shift in under four weeks, and blood pressure in under six weeks.

Small changes matter. Berry points to a King’s College London study, which showed simply replacing a typical unhealthy snack with almonds resulted in a 30% reduction in predicted cardiovascular disease.

Three of the best diets for heart health

1. The DASH diet – best for high blood pressure

The DASH diet (Dietary Approaches to Stop Hypertension) has a strong focus on salt restriction as it was specifically devised to treat high blood pressure. It also limits all the usual baddies, such as sugar, alcohol and processed foods in favour of eating lots of plant-based proteins including legumes, beans, nuts with the occasional addition of seafood and meat.

The diet is rich in fibre, calcium and wholegrains all of which keep cholesterol – and our risk of heart disease – down.

2. The Mediterranean diet – best for those who enjoy a glass of wine

This is less prescriptive than the DASH diet, and is more focused on the Mediterranean way of life, allowing alcohol at mealtimes. Like the DASH diet, it is rich in fresh produce and whole foods: vegetables and fruits, beans and pulses, olive oil, nuts and seeds and fish and chicken. It is also low in saturated fat with limited amounts of dairy, red meat, and processed meat – and an emphasis on good, unsaturated fats, such as lashings of olive oil.

It’s a favourite among health experts and research links it to a reduced risk of heart disease, dementia and Type 2 diabetes.

3. Pescatarian diet – best for fish fans

Loaded with vegetables and fruits as well as fish, this is a high-fibre diet that’s rich in the omega-3 fatty acids which are so good for our hearts. Oily fish in particular, such as salmon and mackerel, are full of these fats, which play an important part in keeping cholesterol levels in check.

Research from the British Medical Journal has shown that eating a pescatarian diet is linked to a lower risk of developing coronary heart disease, than following a diet which contains meat. However, you may be missing out on iron and B12 from red meat and poultry, so supplements are recommended.