#363 Intermittent Fasting: Miracle Diet or Hazardous to Your Heart?

Intermittent Fasting: Miracle Diet or Hazardous to Your Heart?

A recent study involving more than 20,000 adults discovered that people who adhered to an 8-hour time-restricted eating plan, a form of intermittent fasting, were 91% more likely to face a higher risk of dying from heart problems. How could this be? Isn’t intermittent fasting supposed to be heart-healthy, as I’ve previously reported in our 2 best-selling books The Longevity Plan and The AFib Cure? Read on to learn more…

The 91% Higher Risk of Heart Death Intermittent Fasting Study

In this study, scientists looked into how sticking to an 8-hour time-restricted eating plan (a 16 hour fast each day) could affect your health. They reviewed self-reported data about what time people ate each day from 2003 to 2018 in the National Health and Nutrition Examination Surveys (NHANES). Then, they compared it to which people died in the U.S. from 2003 to December 2019, using data from the Centers for Disease Control and Prevention’s National Death Index database.

The people in the study were then followed for 8 years on average, with some being followed for as long as 17 years. And over the 8-year follow-up period those who fasted for at least 16 hours daily were 91% more likely to die from cardiovascular disease.

It is important to know that this study has not yet gone through the peer-review process nor has it been published. It was just an abstract that was presented at an American Heart Association (AHA) meeting on March 18, 2024.

So, why am I discussing a study that hasn’t been published yet? Well, these initial study findings were shared with the press, sparking discussions worldwide. If you’re interested in seeing the complete data presented at this AHA meeting, you can click on this link.

3 Reasons Why This Presentation Was Totally Flawed

1. The study relied only on 20,000 people trying to remember how long they fasted every day for 8 years (at least 16 hours). Personally, I can barely recall how long I fasted from dinner last night until breakfast this morning, let alone my fasting time every day for the past 8 years!

2. The researchers didn’t mention what people were eating during this 8-year period. If their intermittent fasting method was to eat cheeseburgers and fries every night for dinner, that might explain the 91% higher risk of dying from heart disease.

3. This study wasn’t randomized, meaning it’s probable that the people who opted for intermittent fasting were quite different from those who didn’t. For instance, it’s entirely possible that individuals with more health issues decided to try intermittent fasting in this study.

The 1 Big New Finding from This Study

Despite the flaws in this study, it does make me wonder about something significant. Many studies over the years have warned that skipping breakfast isn’t good for your heart or your overall health. For example, in a recent study of 199,634 Americans, regularly skipping breakfast resulted in a 32% increased risk of dying prematurely.

Could it be that the 91% higher risk of dying from heart disease in this study was linked to people skipping breakfast? Is there something crucial in your body’s internal clock that benefits from starting the day with breakfast?

While we’re still lacking solid research on the long-term mortality risks of intermittent fasting, we can turn to existing longevity studies for insights. For instance, in our study of centenarians in China that we covered in our book, “The Longevity Plan,” all of them fasted for at least 12 hours each day. They typically had an early dinner around 6 pm and then didn’t eat until breakfast the next day at around 6 am. Could the key to a longer life be following this pattern: having an early dinner and then fasting for 12 hours until breakfast the next morning?

What Does the Science Really Tell Us About Intermittent Fasting?

To truly grasp the science behind intermittent fasting, we must examine all the randomized controlled trials published. These trials are much more reliable than observational studies, like the one with a 91% increased risk of cardiovascular death we’ve been discussing. In randomized controlled trials, patients in both study groups are similar, making the findings much more credible.

For example, in this recently published meta-analysis study of 130 randomized controlled trials, researchers found the following benefits with intermittent fasting in obese people:

1. Intermittent fasting was beneficial for weight loss. This weight loss benefit was most pronounced in the first 1-6 months of intermittent fasting after which there was limited additional weight loss.

2. LDL (bad cholesterol), total cholesterol, and triglycerides all went down.

3. Fasting glucose and insulin levels both decreased.

4. Blood pressure was lowered.

Although this meta-analysis of 130 randomized controlled trials on intermittent fasting didn’t specifically explore its effects on longevity, the fact that it leads to reductions in weight, cholesterol levels, glucose, insulin, and blood pressure suggests it could be protective against heart disease.

Dr. Day’s Take on Intermittent Fasting

Although a rigid 16-hour intermittent fasting routine may not be suitable for everyone, I’ve observed remarkable changes in some of my patients as a result of it. For a select few, it’s the only eating schedule that has aided in weight loss and alleviated their atrial fibrillation symptoms. Personally, I aim for a 12-hour fasting window each day, as I find it to be most effective for me.

Furthermore, multiple studies suggest that consuming food late at night can negatively impact health. Hence, I advise my patients to refrain from eating after 6 pm. This allows them to fast for a minimum of 12 hours each day, assuming they don’t have breakfast until 6 am. Since most studies highlight the benefits of starting the day with a nutritious breakfast for overall health and longevity, I believe this approach is the most beneficial for my patients.


The information provided in this article is for educational and informational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or dietary regimen.

About the Photo

Last weekend, I snapped this photo capturing my 8-year-old son enjoying his favorite jump off the 9990 ski run at Park City Mountain Resort. Skiing together is our favorite activity, bringing us joy and cherished memories.

Disclaimer Policy: This website is intended to give general information and does not provide medical advice. This website does not create a doctor-patient relationship between you and Dr. John Day. If you have a medical problem, immediately contact your healthcare provider. Information on this website is not intended to diagnose or treat any condition. Dr. John Day is not responsible for any losses, damages or claims that may result from your medical decisions.

  1. I often like to eat late at night, from 9pm until midnight. This is my bad habit.

  2. We fast from 6pm until 10 am for 16 hours and have found it’s the optimum healthy schedule as we don’t eat after 6pm going to bed at 11:30pm and do our cardio at 8am which further takes advantage of autophagy and then have a very nutritious breakfast of my Johnny cakes which contain; rolled oats, soy milk, peaches, banana, cinnamon, flax seeds and chia seeds along with a pea protein/soy milk/water drink.

  3. My heart rhythm is absolutely affected by my attempts at dieting. I typically start with mostly protein the very first week followed by the addition of limited vegetables in subsequent weeks. My c-pap shows an increase of my heart stopping up to an average 12 times per night compared with numbers all under 2. I also end up with a noticeable irregular heartbeat which is normally controlled by medication.
    I am very overweight and am now experiencing additional issues especially in my feet which are exacerbated by lack of exercise. I did try the 16 hour fasting but this did not work for me. There is a limit to what I can endure at this age (71).