What was presented
On 18 March 2024 the American Heart Association highlighted an abstract presented at its Epidemiology and Prevention | Lifestyle and Cardiometabolic Health Scientific Sessions in Chicago. Using diet data from about 20,000 adults in the US National Health and Nutrition Examination Survey (NHANES 2003–2018), people who ate within less than 8 hours a day had a 91% higher risk of cardiovascular death than those eating across 12–16 hours. Median follow-up was about 8 years.
Five limitations
| Limitation | Why it matters |
|---|---|
| Conference abstract, not a peer-reviewed paper at the time | The AHA itself says abstracts are preliminary until published in a peer-reviewed journal |
| Observational | It cannot tell whether the eating window or the life circumstances behind it caused the risk |
| Two days of diet recall | Two 24-hour recalls were treated as years of habit |
| Small exposed group | Reports put the under-8-hour group at about 414 people with 31 cardiovascular deaths |
| Baseline differences | Critics noted differences such as higher smoking rates and BMI in the under-8-hour group |
Critics pointed out that the group may include people squeezing meals between multiple jobs or shifts rather than people fasting on purpose.
So what should you do?
- This one study cannot show that fasting harms the heart. It also does not show that it is safe.
- If you have heart disease or risk factors (high blood pressure, diabetes, smoking), talk to your doctor before shrinking your window to 8 hours or less.
- Randomized trials found only small weight-loss effects from time-restricted eating, so there is little reason to fixate on an 8-hour window. See 16:8 vs 14:10.
Checking your own pattern
Look at your average duration
If your Average duration in Stats is above 16 hours, many of your days have an eating window shorter than 8 hours. Check whether your fasts have crept longer than you intended.
Look at the preset breakdown
If 20:4 and 24h are growing, ask whether that is a choice or a result of a schedule that makes you miss meals. If it is the latter, the issue is your routine, not your fasting plan.
FAQ
Was it later published as a full paper?
This guide is based on the abstract as described by the AHA. A full paper may differ, so check any follow-up publication if one appears.
So is eating over 12 or more hours safer?
An observational study cannot support that either. What and how much you eat, sleep, exercise and smoking matter far more.
Sources: American Heart Association newsroom, 18 Mar 2024 (abstract P192) · TCTMD, critiques of the same study
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