Fasting, feasting: The science behind intermittent fasting

Once touted to be the wonder drug for weight loss and healthy living, the method has recently faced flak for raising the risk of cardiovascular disease

Intermittent fasting, which was believed to be the new formula to achieve wholesome weight loss and a healthy lifestyle, could increase a person's risk of death from cardiovascular diseases, a new unpublished study has highlighted.

Experts point out that while the short-term benefits of intermittent fasting are proven, there is not enough research on the impact in the long run.(istockphoto)

While the findings of the study are being examined, health experts in India are divided over the long-term impacts of intermittent fasting. Some insist that when done correctly, under the guidance of a doctor, it can help achieve health goals, others point out that its effect on a person’s health in the long run could be debilitating.

Last week, an abstract was presented at an American Heart Association Conference claimed that people who followed the common intermittent fasting rule of 16:8 — fasting for 16 hours and eating in a window of eight hours — faced a 91% increased risk of dying from heart disease compared to people who spread their meals over 12 to 16 hours. The abstract also suggested that 7.5% of those who ate within eight hours died from heart disease during the study, compared to 3.6% of those who ate across 12 to 16 hours. The researchers used data from the National Health and Nutrition Examination Survey ((NHANES) in observational research to identify the relationships between lifestyle factors and disease over 15 years. The study is yet to be published in a peer-reviewed journal, which means the claims in the study are uncorroborated.

According to Johns Hopkins documents, intermittent fasting is defined as an eating plan that switches between fasting and eating on a regular schedule. The most acceptable formula is 16:8 but others exist including the 5:2 formula which involves eating regularly five days a week and limiting calorie intake for two days a week. In these two days, a person is required to consume only 500–600 calories against the daily requirement of 2000-3000 calories.

"There are several different ways to do intermittent fasting, but they are all based on choosing regular time periods to eat and fast. For instance, you might try eating only during an eight-hour period each day and fast for the remainder. Or you might choose to eat only one meal a day two days a week. There are many different intermittent fasting schedules," the Johns Hopkins document read.

The abstract showed that the increased risk of cardiovascular death was also seen in people living with heart disease or cancer. Among people with existing cardiovascular disease, an eating duration of "no less than eight but less than 10 hours per day was also associated with a 66% higher risk of death from heart disease or stroke."

“Restricting daily eating time to a short period, such as eight hours per day, has gained popularity in recent years as a way to lose weight and improve heart health,” a statement issued by the American Heart Association read, quoting senior study author Victor Wenze Zhong, a professor and chair of the department of epidemiology and biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China.

The statement added, “However, the long-term health effects of time-restricted eating, including the risk of death from any cause or cardiovascular disease, are unknown.”

So which one is it?

Dr LK Jha, associate director and head, cardiology at Asian Hospital, said that intermittent fasting has been found to have variable effects on various cardiovascular parameters. "It has been shown to lead to fluctuations in blood sugars and ketone levels. It also leads to fluctuations in blood pressure," he said.

However, the observation of its adverse effect on cardiovascular health had to do with the overall lean body mass of the group being observed, he said. Thus, more research is needed, he said.

"Short-term intermittent fasting has beneficial effects like weight loss and better lipid profile but long-term intermittent fasting has shown to almost double the risk of cardiovascular death. This observation is based on overall lean body mass in this group of patients. We need more data before we can say with certainty about its long-term effects," Jha said.

Dr Sukriti Bhalla, consultant, cardiology, at Aakash Healthcare in Delhi said that intermittent fasting, if done right, has shown multiple health benefits.

"Its success would actually depend on how long the fasting is done. Fasting has always been helpful and has long proven benefits but the benefits of fasting can only be achieved if the time after fasting healthy eating habits are maintained," Dr Bhalla said.

She said that people who are fasting should be mindful of excess intake of calories during the non-fasting period. Improvements such as weight loss, improved activity, sugar control, blood pressure control, lowered insulin levels, cholesterol control etc have been seen in patients who have followed intermittent fasting.

Experts point out that while the short-term benefits of intermittent fasting are proven, there is not enough research on the impact in the long run.

At any rate, any sort of "fad diet" assumed on the go without preparing the body, or indeed, knowing what one's body needs, is dangerous. Dr Ravi Prakash, senior consultant, cardiology at the Pushpawati Singhania Research Institute (PSRI Hospital), said that "fad diets" that cause instant and a steep drop in weight might not be the best for a person's heart health in the long run.

Ultimately, weight loss with consistent exercise and a healthy diet will help maintain a healthy lifestyle.

"Restricting your eating window to eight to fewer hours is neither healthy nor is it easy to maintain for long. We have seen that eating small meals at regular intervals has shown better results for weight loss and also cardiovascular health," he said.