Could the clock be ticking against one of the world’s most popular diet trends? A striking new analysis presented before the American Heart Association has found that people who follow a 168 intermittent fasting schedule—fasting for 16 hours and compressing all food intake into an 8-hour window—may face a 91% higher risk of dying from cardiovascular disease compared with those who eat over a more typical 12-to-16-hour span.
What Is 168 Intermittent Fasting?
The 168 method, also known as time-restricted eating, is built on a deceptively simple principle. Practitioners consume no calories for 16 hours, drinking only water, black coffee, or unsweetened tea, before eating during the remaining 8 hours. During the extended fast, the body first draws on stored glycogen; once those reserves run low, it shifts to burning fat, producing ketones in the process. That metabolic switch is precisely why the diet has become a favorite for rapid fat loss.
The Study’s Startling Findings
The research reviewed dietary patterns from more than 20,000 U.S. adults recorded in the National Health and Nutrition Examination Survey between 2003 and 2018, then compared them against mortality data from the U.S. Centers for Disease Control and Prevention through December 2019. The results challenge years of assumptions about the benefits of fasting, revealing five major red flags:
- People who consumed all their food within an 8-hour window had a 91% higher risk of cardiovascular death.
- Those with existing heart disease or cancer also showed rising cardiovascular mortality risk under the regimen.
- Heart disease patients eating between 8 and 10 hours daily saw a 66% greater association with death from heart disease or stroke.
- Time-restricted eating did not lower overall risk of death from any cause.
- Cancer patients who ate over more than 16 hours daily appeared to have a lower risk of cancer mortality.
“Short-Term Benefits, Long-Term Harm”
Lead researcher Dr. Wenze, a professor and director of the Department of Epidemiology and Biostatistics at Shanghai Jiao Tong University’s medical school, was unambiguous. “168 fasting is widely popular for its short-term weight-loss benefits,” he said, “but our study shows that shorter eating windows are not associated with living longer.” In short, fasting may offer quick results at a serious long-term cost.
Not the First Cautionary Tale
This is hardly the first warning. A Taiwanese doctor previously revealed on a medical program the case of a male patient who followed 168 fasting for three months—and ended up with stomach ulcers and severe inflammation. There is also the “rebound overeating” trap: people who restrict for 16 hours often consume two to three times their normal portion in the 8-hour window, completely cancelling any calorie deficit.
Who Should Never Try 168?
Physicians stress that time-restricted eating is not for everyone. Three groups, in particular, should steer well clear:
- People with high daily energy demands, who risk fainting from hypoglycemia.
- Patients with poorly controlled diabetes, whose fluctuating blood sugar makes long fasting windows genuinely dangerous.
- Individuals prone to binge eating, since the compressed feeding window encourages overconsumption.
The Bottom Line
While this study does not condemn every person who fasts, it underscores a critical point: what you eat, and how much, may ultimately matter far more than when you eat. The American Heart Association continues to advocate balanced meals, regular physical activity, and sustainable habits over dietary extremes. For anyone considering 168 fasting, a conversation with a doctor first isn’t just sensible—it may well be life-saving.