Intermittent fasting is a dietary plan which limits a person's food and beverage intake to certain times of the day or week to achieve weight loss. Fasting patterns vary in duration and frequency, with two popular routines including  alternating 24-hour periods of fasting with eating normally  and creating an eight-hour eating window while fasting for the other 16 hours. Many human and animal studies confirm the therapeutic benefits of intermittent fasting, which include increased  longevity, decreased body weight and fat mass, and healthy functioning of the cardiovascular system. 

Prior research includes a systematic review of twenty clinical studies exploring the effect of intermittent fasting on cardiometabolic risk factors in patients with metabolic syndrome. This found that waist circumference, triglycerides, fasting plasma glucose, cholesterol LDL (the bad cholesterol) concentration, and systolic and diastolic blood pressure were significantly improved with intermittent fasting. Maintaining these factors under control can also reduce the risk of cardiovascular diseases. Moreover, intermittent fasting has been shown to reduce the blood level of inflammatory markers, such as homocysteine and c-reactive protein (CRP). The reduction of these markers, along with reduced lipid levels, also  impacts the development of atherosclerotic plaques in arteries.

Efforts to establish a direct positive link between intermittent fasting and the development of heart disease remain a work in progress, with most of our knowledge accumulated from animal studies. These show that mice or rats maintained on an every-other-day fasting diet have a reduced myocardial infarct size after inducing myocardial infarction compared to non-fasting-fed controls. The reduction of infarction was associated with improved survival and recovery of heart functions. More recent studies suggest that the beneficial effects of intermittent fasting on heart disease are triggered through protective mechanisms at the cellular level and enhancing the cell response against stress by the clearance of damaged intracellular components, "autophagy" and generation of new mitochondria. Humans most likely share these  mechanisms with animals.

One of the most widely followed fasting patterns occurs during Ramadan, when Muslims around the world refrain from food and drink from dawn to sunset. Several research studies indicate that intermittent fasting throughout the Holy Month positively affects cardiovascular risk factors in healthy and obese individuals. These include the findings of the London Ramadan Study published in the 2021 edition of the Journal of the American Heart Association, which highlights the  beneficial effects of Ramadan fasting on blood pressure independent of weight and fat mass changes. A prior clinical study examining the effects of Ramadan fasting on the symptoms of  chronic heart failure also found that approximately 92% of patients had no changes or improved symptoms whereas conditions worsened for the remaining 8%. Although this and other clinical studies support the idea that intermittent fasting is safe for most patients with chronic but stable heart illnesses, they should seek personalized advice from  healthcare providers prior to practicing any form of fasting.  

Indeed, all previous human and animal studies were performed for short durations, with  the longer-term impact of intermittent fasting still to be evaluated. A new clinical study by Shanghai’s Jiao Tong University nevertheless suggests that limiting feeding time to eight hours a day and fasting for 16 hours is associated with a higher risk of death from heart disease during an average follow-up period of eight years. The findings are based on the analysis of two surveys of 20000 adults living in the United States which detailed what they ate over a 24-hour period. 

Despite attracting global media interest the study has its limitations, including reliance on self-reported food intake, a practice susceptible to participants' recall biases. Additionally, crucial risk factors such as obesity or hypercholesterolemia and details concerning the nutrient quality of participants' diets were not included in the analysis. With this information, it can be determined if nutrient density might be an alternative explanation for the observed findings on the time window for eating. Without it, we cannot definitively attribute disparities in heart disease-related deaths solely to the length of the eating window. Further clinical trials are required to draw more robust conclusions about the effect of regular fasting on the long-term risk of heart disease. It is also crucial that future  studies determine the optimal fasting period if these diets are to be used as an intervention for preventing cardiovascular disease. 

Dr Ayman Al Haj Zen is an assistant professor at Hamad Bin Khalifa University’s College of Health and Life Sciences.

The thoughts and views expressed are the author’s own and do not necessarily reflect an official University stance.