Fasting and your heart

Heart disease is the leading cause of death worldwide, and most of its risk factors, such as high blood pressure, high cholesterol, excess weight and high blood sugar, respond to how we eat. So it's natural to ask whether fasting helps your heart. The honest answer is that it can improve several risk factors, mostly through weight loss, but we don't yet have trials showing it prevents heart attacks or strokes.

What the trials show

Because so many small trials exist, researchers have started pooling them. An umbrella review brought together 11 meta-analyses covering 130 randomized trials of intermittent fasting. It found improvements in LDL cholesterol, total cholesterol, triglycerides, blood sugar, insulin and blood pressure. But it also found that most of these results rested on low or very low quality evidence, mostly from short trials lasting about three months ¹.

Blood pressure

Losing weight lowers blood pressure, and that's the main way fasting helps. But timing may add something. In a tightly controlled trial, men with prediabetes ate exactly enough to keep their weight stable, either within a 6-hour window ending in the afternoon or across 12 hours. The early window lowered their blood pressure, even though their weight didn't change ³. In another trial, adults with obesity eating between 7 a.m. and 3 p.m. saw their diastolic blood pressure fall by 4 mmHg more than those eating over 12 hours or more ⁴.

Cholesterol: watch your numbers

Most people see their cholesterol improve or stay the same when they fast and lose weight. But not everyone. In a year-long trial comparing alternate-day fasting with daily calorie cutting, LDL cholesterol, the kind that builds up in arteries, had risen more in the fasting group by the end of the year ⁵. What you eat in your window matters: a short window filled with fatty meats and pastries won't help your arteries.

An open question about long fasts

Some observational studies have raised concerns. In a national US study of more than 10,000 adults over 60, those whose daily fast was longer than about 12.4 hours had a higher risk of dying from heart disease than those fasting around 10.5 to 12.4 hours; the lowest risk was at about 11.5 hours ⁶. Fasting time was estimated from just two days of food records, and studies like this can't show cause and effect: people who eat in a short window may differ in their health, income or work in ways the researchers couldn't fully measure. But they're a reminder that longer isn't automatically better, especially for older adults.

Sources

1. Patikorn C, Roubal K, Veettil SK, et al. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open. 2021;4(12):e2139558. doi.org/10.1001/jamanetworkopen.2021.39558
2. Semnani-Azad Z, Khan TA, Chiavaroli L, et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ. 2025;389:e082007. doi.org/10.1136/bmj-2024-082007
3. Sutton EF, Beyl R, Early KS, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212-1221.e3. doi.org/10.1016/j.cmet.2018.04.010
4. Jamshed H, Steger FL, Bryan DR, et al. Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial. JAMA Intern Med. 2022;182(9):953-962. doi.org/10.1001/jamainternmed.2022.3050
5. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med. 2017;177(7):930-938. doi.org/10.1001/jamainternmed.2017.0936
6. Zhang Z, Zhao H, Tao Z, et al. A National Study Exploring the Association between Fasting Duration and Mortality among the Elderly. Nutrients. 2024;16(13):2018. doi.org/10.3390/nu16132018