According to a study, interval fasting increases the risk of death – but experts are skeptical about the results

• According to a recent study from Shanghai, intermittent fasting increases the risk of dying from cardiovascular disease by 91 percent.
• The results of the study will be presented in a poster presentation at the EPI|Lifestyle Scientific Sessions 2024 conference. The data is based on eating habits of 20,000 US Americans
• Experts criticize that these are not causal relationships and that crucial influencing factors are not reported

People who practice intermittent fasting are said to have a 91 percent higher risk of dying from cardiovascular disease. Researchers from the Shanghai Jiao Tong University School of Medicine in Chicago presented this almost unbelievable result at the conference of the American Heart Association.

For the study, the researchers reportedly examined the eating habits of over 20,000 Americans. They used data from people over 20 years of age who took part in the national nutrition survey NHANES between 2003 and 2018. On average, the participants were observed for eight years and compared with the data from the National Death Index.

The results of the study contradict previously published studies. They show that people who eat within a time window of eight hours or less each day have a 91 percent increased risk of dying from cardiovascular disease. This also applies, to a slightly lesser extent, to people who have already been diagnosed with cardiovascular disease and cancer. According to the study, the risk of dying is 66 percent higher for people with cardiovascular disease who only eat within a period of ten hours a day.

Particularly in the case of cancer patients, the results tend to prove the opposite of what was previously assumed. According to the study, if cancer patients spread their food intake over more than 16 hours a day, the risk of dying from cancer actually decreases. “The results of our survey do not support the long-term use of 16:8 intermittent fasting to prevent cardiovascular disease and related deaths,” the researchers write.

The results of the study were presented in advance at the American Heart Association conference. The full study is still in the peer review process and is due to be published soon. Therefore, not all information about the study is yet available. Previous studies suggest that intermittent fasting can help with weight loss and also has other positive health effects, which is why it has become a popular form of diet in recent years. According to experts, intermittent fasting has very different effects depending on the time frame and type of food, so it is difficult to predict general and long-term consequences.

Many scientists doubt the validity of the study: “I consider epidemiological studies in this context to be completely unreliable. Their validity with regard to TRE (time-restricted eating, intermittent fasting – editor’s note) is extremely low. The data is only reported in an overview. What is most confusing is that the observation period is eight to eleven years. However, TRE has only been a more common practice for about three to five years. It must therefore be assumed that there were other reasons for skipping meals,” explained Professor Andreas Michalsen, chief physician for internal medicine at the Immanuel Hospital in Berlin. A case number of 31 cardiovascular deaths is not suitable for deriving values ​​of 91 percent. In addition, there are no basic studies that indicate this effect. “Epidemiological studies with a low level of evidence are not relevant to me here.”

According to Michalsen, skipping meals could also be related to lack of time and other stressors. It is also important to know whether breakfast or dinner was skipped. “Skipping breakfast can lead to ‘gluttony’ in the evening in cardiometabolic diseases, which is unfavorable,” explained Michalsen.

Tillmann Kühn, Professor of Public Health and Nutrition at the University of Vienna, also doubts the validity of the study. The study did not specifically examine intermittent fasting. Skipping meals could also indicate existing illnesses. “The NHANES data that the authors used are very good in principle – unfortunately, they do not record intermittent fasting. The pure time information for food intake on individual days is only of very limited use for this,” explained Kühn. It is not clear whether there is a causal connection or a pure correlation. “Since conscious, intentional intermittent fasting was not examined in the study, no conclusions can be drawn about its effects on different groups of people. Good long-term studies on intermittent fasting are completely lacking. Therefore, neither advantages nor disadvantages are sufficiently proven.

Like Michalsen, Kühn also believes it is possible that the reason for the missing meals could be the diseases themselves. “It is conceivable that people in the study who were suffering more severely from cancer or cardiovascular diseases had restricted their diet due to their diseases. In that case, the disease itself would explain the mortality risk,” explained Kühn.

Stefan Kabisch from the Clinic for Endocrinology and Metabolism Medicine at the Charité University Medicine Berlin sees another connection. The proportion of smokers is highest among people who eat fewer meals. The increased mortality could also be related to low socioeconomic status and other statistically linked factors, such as smoking, alcohol consumption or lack of exercise. “Actually causal factors for mortality may have already existed before the study participants even started intermittent fasting. Obesity, type 2 diabetes and elevated blood lipids often motivate many people to start intermittent fasting,” explained Kabisch. This is also the case in the current study: “The intermittent fasting group has the highest BMI and the highest proportion of smokers. Ethnic distribution also plays a role, because in the USA – where the NHANES cohort was surveyed – African Americans face the greatest health risk, primarily for social reasons.”