Crash diets may stop the heart pumping properly, Oxford University warns

Crash diets may stop the heart pumping properly, a new study by Oxford University has found.

Researchers at Oxford University said people suffering from heart problems should seek medical advice before adopting a low calorie diet, the Daily Telegraph reports.

The new study used magnetic resonance imaging (MRI) to investigate the impact of eating fewer than 800 calories a day on heart function and the distribution of fat in the abdomen, liver, and heart muscle.

Nutritionists recommend that men consume around 2,500 calories a day and women 2,000 calories to maintain a healthy weight. But many people now cut their daily intake by drinking diet-shakes to dramatically to lose weight or drastically cutting meals.

"Crash diets, also called meal replacement programmes, have become increasingly fashionable in the past few years," said lead author Dr Jennifer Rayner, clinical research fellow, Oxford Centre for Magnetic Resonance, at the Oxford University.

"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. But the effects on the heart have not been studied until now."

Recent research found that two thirds of Britons are on a diet most of the time, but there are 800,000 people living with heart failure and nearly two million living with chronic angina.

The research was carried out on 21 obese volunteers, of an average age of 52 and BMI of 37.

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 after one and eight weeks.

After one week, total body fat, visceral fat and liver fat had all significantly fallen by an average of 6 per cent, 11 per cent, and 42 per cent, respectively, 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 per cent and there was a noteable deterioration in heart function, including the heart's ability to pump blood.

Dr Rayner said: "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. 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 added.

"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."

The researchers warned that in people with existing heart problems crash dieting might exacerbate their condition – for example aggravating heart failure symptoms like shortness of breath or increasing the risk of arrhythmias.

Dr Rayner said: "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. Caution is needed in people with heart disease."

The research was presented at CMR 2018, the annual meeting of the European Society of Cardiology.