Crash diets or fasting may be bad for the heart, study suggests

CRASH diets could stop the heart pumping properly and people suffering from cardiac problems should seek medical advice before adopting a low calorie or fasting diet, a study suggests.

Oxford University researchers 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.

“Crash diets have become increasingly fashionable in the past few years,” said Dr Jennifer Rayner, clinical research fellow at the Oxford Centre for Magnetic Resonance.

“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 people are on a diet most of the time, but there are also 800,000 people living with heart failure and nearly two million living with chronic angina. The research was carried out on 21 obese volunteers, with an average age of 52 and BMI of 37. They 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 notable 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 continued.

“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.”

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.”

‘If you have heart problems, check with your doctor before embarking on a very low calorie diet or fasting’