Are crash diets risky for the heart? Study links low-calorie diets and meal replacement programs with worsening of heart functions

By Nathan Gray

- Last updated on GMT

iStock / 5second
iStock / 5second

Related tags Obesity

A debate has broken out about the potential risks and benefits of very low calorie diets (VLCDs) and meal replacement programs after data presented at a European congress suggested they could cause temporary deterioration in heart functions.

The research, presented at CMR 2018 in Barcelona, used magnetic resonance imaging (MRI) to investigate the impact of a very low calorie diet on heart function and the distribution of fat in the abdomen, liver, and heart muscle. , and sponsored by the British Heart Foundation

Led by Dr Jennifer Rayner from the University of Oxford, the study suggests that crash diets can a transient deterioration in heart function after the first week of diet – however the data also showed improvements in heart functioning by week eight of the study.

“Crash diets, also called meal replacement programmes, have become increasingly fashionable in the past few years,” ​said Rayner.

“These diets have a very low calorie content of 600 to 800 kcal per day and can be effective for losing weight, reducing blood pressure, and reversing diabetes,”​ she added. “But the effects on the heart have not been studied until now.”

“If you have heart problems, you need to check with your doctor before embarking on a very low calorie diet or fasting. People with a cardiac problem could well experience more symptoms at this early time point, so the diet should be supervised.”

However, Professor Anthony Leeds, medical director of the Very Low Calorie Diet (VLCD) Industry Group noted that previous research including a full clinical trial known as the ‘cut-it trial’ showed effective weight loss and improved heart function.

I welcome any scientific studies that help us to continue to deliver VLCDs and LCDs safely and effectively,” ​said Leeds.

Rayner added that very low calorie diets do have benefits and do not need to be avoided – especially in healthy people.

“Healthy people may not notice the change in heart function in the early stages,”​ she said. “But caution is needed in people with heart disease.”

Oxford study

The new study included 21 obese volunteers with an average age of 52 years, and an average body mass index of 37 kg/m2​.

Participants consumed a very low calorie diet of 600 to 800 kcal per day for eight weeks. MRI was performed at the start of the study and again after weeks one and eight.

After one week, total body fat, visceral fat and liver fat had all significantly fallen by an average of 6%, 11%, and 42%, respectively.

This was accompanied by significant improvements in insulin resistance, fasting total cholesterol, triglycerides, glucose and blood pressure.

However, after one week, heart fat content had risen by 44%, said those behind the study.

By eight weeks, heart fat content and function had improved beyond what they had been before the diet began and all other measurements including body fat and cholesterol were continuing to improve, said the team.

“The metabolic improvements with a very low calorie diet, such as a reduction in liver fat and reversal of diabetes, would be expected to improve heart function,”​ said Rayner. “Instead, heart function got worse in the first week before starting to improve.”

“The sudden drop in calories causes fat to be released from different parts of the body into the blood and be taken up by the heart muscle,”​ she noted.

“The heart muscle prefers to choose between fat or sugar as fuel and being swamped by fat worsens its function. After the acute period in which the body is adjusting to dramatic calorie restriction, the fat content and function of the heart improved.”

Professor Leeds noted that guidance on best practice should be based on extensive full scale statistically robust clinical trials.

 “Members of the VLCD Industry Group have been engaged with centres of cardiological excellence for some years and work closely with those best placed to generate gold standard evidence

Rayner added that more research is needed to discover the impact of the short-term reduction in heart function.

She noted that in people with existing heart problems it might exacerbate their condition – for example aggravating heart failure symptoms like shortness of breath or increasing the risk of arrhythmia's.

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