Crash diets, also called meal replacement programs, have become increasingly fashionable in the past few years.
A recent study from University of Oxford shows that crash diets can weaken heart function.
People with heart disease should seek medical advice before adopting a very low calorie diet.
Crash diets often 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.
In the study, researchers used magnetic resonance imaging (MRI) to examine the impact of a very low calorie diet on heart function and the distribution of fat in the abdomen, liver, and heart muscle.
The study included 21 obese volunteers. The average age was 52 years.
They ate 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.
The researchers found that after one week, total body fat, visceral fat and liver fat had all significantly fallen by an average of 6%, 11%, and 42%, respectively.
In addition, there were significant improvements in insulin resistance, fasting total cholesterol, triglycerides, glucose and blood pressure.
However, after one week, heart fat content had risen by 44%. This was linked to a deterioration in heart function, including the heart’s ability to pump blood.
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.
The team suggests that the metabolic improvements with a very low calorie diet, such as a reduction in liver fat and reversal of diabetes.
But the heart function got worse in the first week before starting to improve.
This is because 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.
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.
But in people with existing heart problems, it might worsen their condition — for example aggravating heart failure symptoms like shortness of breath or increasing the risk of arrhythmias.
The team suggests that more research is needed to discover the impact of the acute reduction in heart function.
The important thing is if you have heart problems, you need to check with your doctor before embarking on a very low calorie diet or fasting.
Otherwise healthy people may not notice the change in heart function in the early stages.
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News source: European Society of Cardiology (ESC).
Figure legend: This Knowridge.com image is for illustrative purposes only.
