Intermittent Fasting May Carry Significant Health Risks

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Time-restricted eating (TRE) is one form of intermittent fasting, involving limitations on the hours during which food is consumed within a 24-hour period. This dietary approach emphasizes not the quality or quantity of food but its timing. The most commonly practiced scheme is 16:8, meaning 16 hours of fasting followed by an 8-hour eating window without other restrictions.

In recent years, this diet has become popular due to its common association with weight loss. Previous research also suggested it might improve some cardiometabolic health indicators, such as blood pressure, blood glucose levels, and cholesterol. However, according to the study results presented in poster form at the AHA Congress, these benefits are likely only short-term rather than long-term health benefits.

An 8-year Study Cohort

The cohort studied included over 20,078 American adults over 20 years of age who participated in the National Health and Nutrition Examination Surveys (NHANES) from 2003 to 2018. Their average age was 48 years, with 50% men and 73% non-Hispanic whites. Included in the analysis were those who completed a dietary questionnaire twice in the first year, detailing their 24-hour eating regimen. Based on this, they were assigned to groups with a daily eating window of no more than 8 hours or 12–16 hours.

On average, respondents’ eating habits were followed for 8 years, during which 2,797 deaths were recorded (of which 840 were from CV causes and 643 from cancer).

Key Findings: Does Timing of Food Matter?

The authors of the study were surprised to find that time-restricted eating may not lead to longer life but, on the contrary, may significantly shorten it. Participants who ate within an 8-hour daily window showed a 91% higher risk of CV death than those who ate within the usual 12–16-hour window (hazard ratio [HR] 1.91, 95% confidence interval [CI] 1.20–3.03). This finding applied to the general population as well as to those with preexisting cardiovascular conditions (HR 2.07; 95% CI 1.14–3.78) and cancer (HR 3.04; 95% CI 1.44–6.41).

No significant difference was found with other time windows compared to the regular 12–16-hour window, except in individuals with CV disease and a daily eating period of no more than 10 hours, who showed a 66% higher risk of CV death or stroke than those on a regular eating schedule. Conversely, eating for more than 16 hours daily was associated with a lower risk of cancer death in cancer patients.

Discussion and Conclusion

Questions remain regarding the study’s methodology. A positive aspect was that the authors could work with a vast epidemiological dataset, but this also represents a limitation. The studied questionnaires were based on self-reported records, potentially influenced by recall accuracy or participants’ tendencies to idealize their eating habits. Moreover, they were based on records from only two days.

The research also does not address a fundamental question—what mechanism underlies the observed association—describing only correlation, not causation. Reverse causality may also play a role, as this type of eating may be more commonly chosen by individuals who are prone to skipping meals or have generally unhealthy eating habits.

A possible explanation for the increased CV death risk is the high intake of nutritionally poor foods, though this hypothesis needs further investigation. Partial findings by the study authors suggest that those who practiced TRE for 8 or fewer hours had less lean mass than those on a regular eating schedule. Loss of lean mass (particularly muscle) could be associated with higher cardiovascular mortality.

Another important factor is that the 8-hour eating group included more smokers and men, which may have significantly influenced the results.

Based on this study, no decisive dietary recommendations can be made; the findings require confirmation in further studies. However, they at least suggest a more cautious approach to TRE and personalization of its regimen, particularly for individuals with CV or cancer conditions. It should also be noted that the study has not yet been published and has therefore not undergone standard peer review.

Editorial Team, Medscope.pro

Sources:

1. 8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death. American Heart Association, 2024 Mar 19. Available at: https://newsroom.heart.org/news/8-hour-time-restricted-eating-linked-to-a-91-higher-risk-of-cardiovascular-death
2. Brooks M. Intermittent fasting linked to higher CVD death risk. Medscape, 2024 Mar 19. Available at: www.medscape.com/viewarticle/intermittent-fasting-linked-higher-cvd-death-risk-2024a1000559