Intermittent fasting has become a popular weight-loss method in recent years. However, a study of more than 20,000 Americans found that individuals who restricted eating to within an eight-hour window had a 91 percent higher risk of death from cardiovascular disease.
On March 18, the preliminary report of this study was presented at a meeting held by the American Heart Association, but it has not yet been published in a peer-reviewed academic journal.
For individuals with existing heart disease or cancer, practicing 16:8 intermittent fasting was associated with a higher risk of dying from cardiovascular disease. Conversely, cancer patients with a daily eating window exceeding 16 hours were at a lower risk of cancer-related death.
Additionally, among those with cardiovascular disease, a daily eating window of eight to 10 hours was linked to a 66 percent increased risk of death from heart disease or stroke.
Victor Wenze Zhong, one of the study’s authors and a professor at Shanghai Jiao Tong University in China, stated that time-restricted eating does not necessarily lead to a longer lifespan compared to the typical eating window of 12 to 16 hours per day. It is particularly important for those with heart conditions or cancer to understand the link between an eight-hour eating window and the risk of death. However, he also emphasized that this study does not imply that time-restricted eating caused cardiovascular death.
It is worth noting that the survey method used in this study has limitations. Participants were asked to fill out questionnaires twice in the first year, recalling their diet from the previous day. This means that the participants’ eating patterns were determined based on only two days. Furthermore, the reported dietary information in the questionnaire does not rule out memory bias and cannot represent the typical eating patterns during the survey period.
In the news release, Christopher D. Gardner, a professor at Stanford University, expressed anticipation for the formal publication of the study. He hopes that this will reveal more dietary details of the participants, shedding light on the reasons behind the findings. Mr. Gardner pointed out that it is currently unclear what factors lead to increased cardiovascular disease mortality among those with shorter eating times.
Mixed Views on the Benefits of Fasting for Cardiovascular Health
This study has indeed sparked public attention. Dr. Yang Jingduan, CEO of the New York Northern Medical Center, highlighted on his health program that many past studies have found that intermittent fasting can increase the body’s sensitivity to insulin, reduce the risk of Type 2 diabetes, and lower inflammation, all of which are beneficial to cardiovascular health. However, the findings of this latest study contradict previous claims that intermittent fasting is beneficial to health, confusing the public.Dr. Yang stated in his program it is evidently unreasonable to draw conclusions about 10-year health outcomes based on the recollection of eating habits over just two days. Additionally, during the study period, the concept of 16:8 intermittent fasting was not yet prevalent. Those with shorter eating times may not have adopted this eating pattern for health reasons—it could have been due to poor lifestyle habits, leading them to simply overlook meal times.
He also emphasized that since this study has not been formally published in an academic journal, it should not be considered a conclusive result. He added that “the sensationalization of the findings by some media reports is irresponsible.”
However, some doctors believe that while 16:8 intermittent fasting may aid in weight loss, it may not necessarily be beneficial for the heart.
Fasting Does Not Always Lower Blood Sugar and May Lead to Muscle Loss
In recent years, the medical community has conducted numerous clinical trials on fasting. However, the varying experimental methods have led to inconsistent results, and there is still no consensus on the impact of fasting on cardiovascular disease.Participants in the study who were obese were randomly assigned to two groups—one group practiced 16:8 intermittent fasting, which involved fasting from 8 p.m. to 12 p.m. the next day, skipping breakfast—while the other group ate three meals a day. After 12 weeks, participants in the 16:8 fasting group lost more weight, but most of the weight loss was from muscle, with minimal fat reduction. The decrease in muscle mass not only reduced physical strength but also increased the risk of weight regain.
Additionally, when comparing other metabolic markers such as blood sugar, insulin, and lipids, 16:8 intermittent fasting did not result in greater improvements compared to the three-meals-a-day group. The study suggested that without changing the diet content, 16:8 intermittent fasting did not offer significant weight loss or cardiometabolic benefits.
Skipping Breakfast May Harm the Heart
It is worth noting that the eating window in the 2020 study mentioned earlier was restricted from 12 p.m. to 8 p.m., which is not the optimal choice from a circadian rhythm perspective. The researchers reasoned that for most people, skipping breakfast might be easier than skipping dinner.Avoid Starvation for Weight Loss and Focus on Eating Nutritious Foods
Dr. Liu discovered from his own experience that 16:8 intermittent fasting is not suitable for everyone. Several years ago, he tried this fasting method but found it very difficult to endure not eating for 16 hours, so he could only fast for 14 hours. Within two months, he lost 4.41 pounds (two kilograms), but his cholesterol levels, an important indicator of cardiovascular disease, remained the same. He experienced significant hunger during the fasting period, leading him to eat more high-sugar, high-fat foods and meat during the eating window.He believes that 16:8 intermittent fasting, which focuses on extending the fasting period, is indeed helpful for weight loss. However, the types of foods consumed have a greater impact on cardiovascular health. Additionally, overeating after fasting can increase the burden on the heart.
Dr. Liu often advises his patients who need to lose weight, “You must not starve yourself to lose weight—starvation will not lead to success.” He emphasized that during weight loss, one should focus on eating more nutrient-rich foods that provide a sense of fullness, such as vegetables, protein-rich foods like fish and skinless chicken, and healthy fats like olive oil and nuts. For those without diabetes, increasing fruit intake is also advisable. At the same time, one should limit the eating of refined carbohydrates, fried foods, foods high in saturated fats, and red meat, as excessive intake of these foods can be detrimental to cardiovascular health.
In addition to consuming more healthy foods, Dr. Liu also offers the following advice for those using 16:8 intermittent fasting for weight control:
1. Regularly monitor lipid, blood sugar, and blood pressure levels to assess the impact of weight loss on cardiovascular health.
2. The timing of fasting is crucial—fasting in the evening is healthier than fasting in the morning.
3. Engage in moderate exercise and eat more protein to promote muscle growth and fat loss.
