Calgary Herald

Should we slow down when it comes to fasting?

The intermitte­nt dieting trend may pose risks to your heart, according to a recent study


Intermitte­nt fasting — when people only eat at certain times of day — has exploded in popularity in recent years. But now a surprising new study suggests that there might be reason to be cautious: It found that some intermitte­nt fasters were more likely to die of heart disease.

The findings were presented in March at an American Heart Associatio­n meeting in Chicago and focused on a popular version of intermitte­nt fasting that involves eating all your meals in just eight hours or less — resulting in at least a 16-hour daily fast, commonly known as “time-restricted” eating.

The study analyzed data on the dietary habits of 20,000 adults across the United States who were followed from 2003 to 2018. They found that people who adhered to the eight-hour eating plan had a 91 per cent higher risk of dying from heart disease compared to people who followed a more traditiona­l dietary pattern of eating their food across 12 to 16 hours each day.

The scientists found that this increased risk also applied to people who were already living with a chronic disease or cancer. People with existing cardiovasc­ular disease who followed a time-restricted eating pattern had a 66 per cent higher risk of dying from heart disease or a stroke. Those who had cancer meanwhile were more likely to die of the disease if they followed a time-restricted diet compared to people with cancer who followed an eating duration of at least 16 hours a day.

The study results suggest that people who practice intermitte­nt fasting for long periods of time, particular­ly those with existing heart conditions or cancer, should be “extremely cautious,” said Victor Wenze Zhong, the lead author and the chair of the department of epidemiolo­gy and biostatist­ics at the Shanghai Jiao Tong University School of Medicine in China.

“Based on the evidence as of now, focusing on what people eat appears to be more important than focusing on the time when they eat,” he added.

Zhong said that he and his colleagues conducted the new study because they wanted to see how eating in a narrow window each day would impact “hard end points” such as heart disease and mortality. He said that they were surprised by their findings.

“We had expected that longterm adoption of eight-hour time restricted eating would be associated with a lower risk of cardiovasc­ular death and even all-cause death,” he said.

The data didn't explain why time-restricted eating increased a person's health risks. But the researcher­s did find that people who followed a 16:8 time-restricted eating pattern, where they eat during an eight-hour window and fast for 16, had less lean muscle mass compared to people who ate throughout longer periods of the day. That lines up with a previous clinical trial published in JAMA Internal Medicine, which found that people assigned to follow a time-restricted diet for three months lost more muscle than a control group that was not assigned to do intermitte­nt fasting.

Holding onto muscle as you age is important. It protects you against falls and disability, and can boost your metabolic health. Studies have found that having low muscle mass is linked to higher mortality rates, including a higher risk of dying from heart disease, said Zhong.

He stressed that the findings were not definitive. The study uncovered a correlatio­n between time-restricted eating and increased mortality, but it could not show cause and effect. It's possible, for example, that people who restricted their food intake to an eight-hour daily window had other habits or risk factors that might explain their increased likelihood of dying from heart disease. The scientists also noted that the study relied on self-reported dietary informatio­n. It's possible that the participan­ts did not always accurately report their eating durations.

Intermitte­nt fasting has been widely touted by celebritie­s and health experts who say it produces weight loss and a variety of health benefits. Another form of intermitte­nt fasting involves alternatin­g fasting days with days of eating normally. Some people follow the 5:2 diet, in which they eat normally for five days a week and then fast for two days.

But time-restricted eating is generally considered the easiest form of intermitte­nt fasting for people to follow because it doesn't require full-day fasts. It also typically doesn't involve excessive food restrictio­n. Adherents often eat or drink whatever they want during the eight-hour eating period — the only rule is that they don't eat at other times of day.

Some of the earliest studies on time-restricted eating found that it helped prevent mice from developing obesity and metabolic syndrome. These were followed by mostly small clinical trials in humans, some of which showed that time-restricted eating helped people lose weight and improve their blood pressure, blood sugar and cholestero­l levels. These studies were largely short-term, typically lasting one to three months, and in some cases showed no benefit.

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