The time-restricted eating (TRE) has emerged as a popular behavioral intervention with the potential to offer various health benefits, from weight management to metabolic health improvements. However, a recent press release from the American Heart Association (AHA) has cast doubt on the safety of TRE, alleging a substantial increase in the risk of cardiovascular death associated with TRE.

A consortium of international experts specializing in time-restricted eating, intermittent fasting, temporal eating patterns, circadian biology, design and implementation of clinical trials, and epidemiological methods and data analysis has conducted analysis of the study’s available data, uncovering several critical flaws that undermine its credibility.

Here is the full letter to the public:

March 27, 2024

Dear readers,

On March 19, 2024, the American Heart Association issued a press release from an ongoing conference (EPI|Lifestyle Scientific Sessions in Chicago) with the title “8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death.” This release received a large amount of media coverage including the BBC, Washington Post, NBC, Medscape, and more. Typically, such headlines are released after a full manuscript detailing the study has been published in a “peer-reviewed” scientific journal. Peer-review is a process in which several experts in the field will critically review the study design, methods (including statistical analysis), the data/results, and the conclusions of the study. This process is essential to ensure the quality of the scientific approach, the credibility of the results, a reasonable interpretation of the data, and implications for future research and patients’ health. Unfortunately, the study that made headlines in the press release did not undergo this process before the press release was issued. As for all studies presented at AHA Scientific Sessions, AHA-assigned reviewers performed a simple review of a short summary of the study submitted by the study investigators (2,500-character limit; about 360-630 words, aka an abstract). This study was selected for poster presentation at the conference AND for a pre-presentation press release. Poster presentations are a great way to share preliminary data and exchange ideas with other scientists at a scientific forum. Abstract content and unreviewed preliminary data presented in posters should not be used for press releases as they can convey misleading information to the public. In this case, there are serious study design limitations that undermine the claims made in the poster title and short abstract submitted to the AHA. Subsequently, these claims were echoed by major media outlets, despite nuances and caveats mentioned in the AHA press release. Media promotion of studies whose full set of methods and results are insufficiently peer-reviewed undermines the credibility of the scientific community. Unfortunately, the press release did not make it clear that this study was not endorsed by the AHA and does not recommend changes to existing nutrition guidelines. This occurrence has raised a false alarm and undue panic among people practicing intermittent fasting, including time-restricted eating, and prospective participants recruited to ongoing, NIH-funded clinical trials of intermittent fasting.

We are an international group of scientists with expertise in time-restricted eating, intermittent fasting, temporal eating patterns, circadian biology, design and implementation of clinical trials, and epidemiological methods and data analysis that have come together to respond to these misleading claims.

Here are a several examples of many flaws in the approach used in this study:

1. The study improperly adjusted for the smoking status of the participants.
   Tobacco is the leading cause of death in the U.S. In this study, there were 60% more smokers in the group eating less than 8 hours per day compared to the reference group. Residual confounding by smoking could in fact account for the elevated cardiovascular mortality risk reported in this study. Importantly, improperly adjusting for smoking has already been reported multiple times to produce false associations with mortality. These factors highlight the need for rigorous methods to properly account for this parameter in studies where death is the outcome.

2. Other important confounders were unaccounted for, which could contribute to the increased risk in the less than 8-hour group.
   The eating duration groups were racially/ethnically unbalanced, with 250% more Black Americans (23.2% vs. 6.6%) in the group eating less than 8 hours daily. There are well- documented racial/ethnic disparities in most causes of mortality in the US [1]. Other contributors such as sleep patterns and shift work, known to be associated with both irregular meal timing and increased mortality, were also not accounted for.

3. The method used to define eating duration is not representative of long-term eating patterns.
   People’s habitual eating habits were evaluated based on two days of a dietary recall questionnaire obtained at a single time point with the assumption that this pattern of eating is consistent over many years (e.g., 2-16 years). The limitations to this assumption are well-documented in nutrition literature as well as the lack of reliability of dietary recall to accurately represent people’s daily eating habits [2]. Importantly, eating times of less than 8 hours on food recall questionnaires are commonly due to incomplete food records rather than a true short eating window.

4. Practicing time-restricted eating (TRE) requires a consistent routine of 8-10 hours of daily eating during many weeks/months. Eating over a period of less than 8 hours on a single day, or two days, is not the same as practicing TRE.
   Eating at different times each day was not accounted for in this study when studies have shown that high variability in meal times is associated with detrimental health outcomes. In addition, in TRE, the eating window is typically aligned with times of day when people are active (not too early or late at night). In this study, the start and end time of the eating window and last eating episode relative to sleep timing were not accounted for. This is important because both breakfast skipping and late eating (e.g., after 9pm) have been associated with increased cardiovascular risk [3].

5. There was an inadequate number of participants in the short eating group
   The sample size (number of participants) for the group eating less than 8 hours daily was too small with only 2% of the population they evaluated. The low number of participants increases the chances of getting a false result.

In contrast to the conclusion of this study, over 100 published peer-reviewed clinical trials have reported that TRE has small to large metabolic health benefits, or little effects, but no study observed serious adverse health outcomes of TRE. Meta-analyses of clinical trials show that TRE reduces body weight and improves blood pressure [4, 5]. Moreover, multiple studies in animals show that TRE extends lifespan [6,7].

Dissemination of alarming headlines about findings without rigorous peer-review is dangerous to public health, healthcare messaging, trust in the scientific community, and ongoing clinical trials. We urge all scientific communities to support responsible and careful communication of study findings and ensure the thorough peer-review of the complete study methods, data, results, and conclusions. Not doing so can lead to misleading and over-dramatized media coverage and long-term damage to the field.

Sincerely,

34 experts in time-restricted eating, intermittent fasting, temporal eating patterns, clinical trials, and epidemiological methods

Emily Manoogian, Ph.D., Salk Institute for Biological Studies

Courtney Peterson, Ph.D., University of Alabama

Mary Playdon, Ph.D., MPH, University of Utah

Krista Varady, Ph.D., University of Illinois Chicago

Kelsey Gabel, PhD., University of Illinois Chicago

Leonie Heilbron, Ph.D., University of Adelaide

Michael Wilkinson, M.D., University of California San Diego Medical School

Tinh-Hai Collet, M.D., University of Geneva

Rafael de Cabo, Ph.D., National Institutes of Health, National Institute on Aging

Dorothy D Sears, Ph.D., Arizona State University

Julie Pendergast, Ph.D., University of Kentucky

Eric Ravussin, Ph.D., Pennington Biomedical Research Center

Amber Kleckner, Ph.D., University of Maryland

John Hawley, Ph.D., Australian Catholic University

Evelyn Parr, Ph.D., Australian Catholic University

Jonas Salling Quist, Ph.D., Steno Diabetes Center Copenhagen

Anne-Ditte Termannsen, MSc, Steno Diabetes Center Copenhagen

Kristine Faerch, Ph.D., Novo Nordisk A/S

Sheri L. Johnson, Ph.D. University of California Berkeley

Omar Mesarwi, M.D., University of California San Diego Medical School

Paula Desplats, Ph.D., University of California San Diego

John Hogenesh, Ph.D., Cincinnati Children’s Hospital Medical Center

Charna Dibner, Ph.D., University of Geneva

Dara L. James, Ph.D., MS, Arizona State University

Catherine Marinac, Ph.D., Harvard Medical School, Dana Farber Cancer Institute

Iwona Swiatkiewicz, M.D., Ph.D., University of California San Diego

Adriana Coletta, Ph.D., MS, RD, University of Utah

Sheetal Hardikar, Ph.D., MBBS, MPH, University of Utah

Amandine Chaix, Ph.D., University of Utah

Blandine Laferrère, M.D., Columbia University Irving Medical Center

Lisa Chow, M.D. MS, University of Minnesota

Phyllis Zee, M.D., Ph.D. Northwestern University Feinberg School of Medicine

Pam Taub, M.D., University of California San Diego Medical School

Satchidananda Panda, Ph.D., Salk Institute for Biological Studies

References

1. GBD US Health Disparities Collaborators. Life expectancy by county, race, and ethnicity in the USA, 2000-19: a systematic analysis of health disparities. Lancet. 2022 Jul 2;400(10345):25-38. doi: 10.1016/S0140-6736(22)00876-5. Epub 2022 Jun 16. PMID: 35717994; PMCID: PMC9256789.
2. Peterson LM, Lee H, Huybrechts I, Biessy C, Neuhouser ML, Haaland B, Krick B, Gunter M, Schulze MB, Jannasch F, Coletta AM, Hardikar S, Chaix A, Bauer CX, Xiao Q, Playdon, MC. Reliability estimates for assessing meal timing derived from longitudinal repeated 24-hour dietary recalls. Am J Clin Nutr. 2023; 117(5):964-975. PMID: 36921904 PMCID: PMC10206325
3. Palomar-Cros A, Andreeva VA, Fezeu LK, Julia C, Bellicha A, Kesse-Guyot E, Hercberg S, Romaguera D, Kogevinas M, Touvier M, Srour B. Dietary circadian rhythms and cardiovascular disease risk in the prospective NutriNet-Santé cohort. Nat Commun. 2023 Dec 14;14(1):7899. doi: 10.1038/s41467-023-43444-3. PMID: 38097547; PMCID: PMC10721609.
4. Elortegui Pascual P, Rolands MR, Eldridge AL, Kassis A, Mainardi F, Lê KA, Karagounis LG, Gut P, Varady KA. A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity (Silver Spring). 2023 Feb;31 Suppl 1(Suppl 1):9-21. doi: 10.1002/oby.23568. Epub 2022 Nov 8. PMID: 36349432; PMCID: PMC10098946.
5. Wang W, Wei R, Pan Q, Guo L. Beneficial effect of time-restricted eating on blood pressure: a systematic meta-analysis and meta-regression analysis. Nutr Metab (Lond). 2022 Nov 8;19(1):77. doi: 10.1186/s12986-022-00711-2. PMID: 36348493; PMCID: PMC9644535.
6. Acosta-Rodríguez V, Rijo-Ferreira F, Izumo M, Xu P, Wight-Carter M, Green CB, Takahashi JS. Circadian alignment of early onset caloric restriction promotes longevity in male C57BL/6J mice. Science. 2022 Jun 10;376(6598):1192-1202. doi:10.1126/science.abk0297. Epub 2022 May 5. PMID: 35511946; PMCID: PMC9262309.
7. Ulgherait M, Midoun AM, Park SJ, Gatto JA, Tener SJ, Siewert J, Klickstein N, Canman JC, Ja WW, Shirasu-Hiza M. Circadian autophagy drives iTRF-mediated longevity. Nature. 2021 Oct;598(7880):353-358. doi: 10.1038/s41586-021-03934-0. Epub 2021 Sep 29. PMID: 34588695; PMCID: PMC9395244.