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Very Low Calorie Diet Warning

Timothy Boyer Ph.D.'s picture
Crash dieting can affect the heart

Adopting a very low calorie diet program for losing weight can be harmful for this category of dieters.


New research presented at a 2018 Cardiovascular Magnetic Resonance Society meeting warns that before embarking on a very low calorie type crash diet, dieters with heart disease should consult with their doctors first due to that the diet may actually adversely affect their heart function.

According to a news release by European Society for Cardiology, until recently, no one has looked at how crash dieting can affect the heart.

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

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"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."

Those effects she refers to turned out to be worrisome concerns as investigators found that heart function during the early stages of crash dieting may worsen before improving.

In the study, 21 obese volunteers were placed on a very low calorie diet of 600-800 calories per day for eight weeks, during which MRI was used periodically to follow the distribution of fat around the abdomen, liver and heart as the diet and weight loss progressed.

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During the first week, then study participants benefitted from weight loss as seem by MRI exams revealing an average loss of 6%, 11%, and 42%, of total body fat, visceral fat and liver fat respectively, as well as the participants showing significant improvements in insulin resistance, fasting total cholesterol, triglycerides, glucose and blood pressure.

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However, after one week, the researchers also found that heart fat content had risen by 44%, which was associated with an overall deterioration in heart function--including the heart's ability to pump blood.

The good news is that by the end of the 8-week long study, the participants' heart fat content had lowered to less than what the fat content had been before the diet began, with an improvement in heart function, as well as continuing body fat and cholesterol improvements.

"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," stated Dr Jennifer Rayner.

"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."

The researchers state that additional study is needed to investigate this finding due to concerns that the rather sudden impact on heart function during crash dieting could exacerbate existing cardiac-related problems like shortness of breath or increasing the risk of arrhythmias.

"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," advises Dr. Rayner, who adds that this does not mean that very low calorie diets should be avoided.

"Otherwise 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."

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European Society of Cardiology (ESC) news release. "Crash diets can cause transient deterioration in heart function."

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