The Short Answer: Research shows that fasting for 13 or more hours overnight may lower cancer risk, improve sleep quality, and reduce inflammation and blood sugar levels. However, this approach isn’t suitable for everyone, particularly those with blood sugar dysregulation or adrenal challenges, and should be approached gradually under professional guidance.

How a 13-hour overnight fast may lower disease risk

Want an easy way to lower your risk of cancer and chronic disease? Eat an early dinner and see if you can comfortably go 13 hours until breakfast.

Research shows that extended fasting overnight may improve cancer outcomes and lower overall cancer risk. Fasting has also been shown to decrease the risk for diabetes and heart disease—conditions that commonly co-occur with autoimmune conditions.

Researchers analyzed more than ten years of data from breast cancer patients in the first study of its kind, showing some striking correlations. Women who fasted less than 13 hours per night showed a 36 percent increase in cancer recurrence compared to those who fasted for 13 or more hours per night.

In other words, if you can comfortably last about 13 hours between dinner and breakfast, it may lower your overall disease risk.

The research examined sleep habits and diets, blood sugar and inflammation markers (serum hemoglobin A1c and C-reactive protein), and cancer outcomes. For people managing autoimmune conditions, including those with Hashimoto’s low thyroid, these markers directly affect flare severity and long-term health.

Extended fasting improves sleep and reduces chronic inflammation

The study showed that longer fasting times also increased the amount of sleep people got at night. This matters because better sleep supports a healthier sleep-wake cycle, or circadian rhythm. A circadian rhythm that is out of balance increases the risk of cancer and many chronic diseases, including autoimmune flares.

Increased fasting time also lowered blood sugar and reduced inflammation, two key factors in managing autoimmune conditions and preventing diabetes and heart disease.

Chronic inflammation and blood sugar dysregulation drive many serious health conditions: heart disease, some forms of cancer, dementia, Alzheimer’s, and Parkinson’s disease.

When extended nighttime fasting isn’t the right approach

While research shows the benefits of extended nighttime fasting, this approach is not for everyone. For those with blood sugar dysregulation or adrenal challenges, longer fasts can be counterproductive and do more harm than good.

If your blood sugar drops too low, fasting can cause insomnia, mood disturbances, fatigue, and poor cognitive function, not to mention intense hunger. If fasting that long makes you feel anything but good, it may be something you need to work toward gradually by first stabilizing your blood sugar.

A primary symptom of low blood sugar is waking up anxious at 3 or 4 a.m. Eating a little protein before bed can help prevent early morning wake-ups. You also need to follow a blood-sugar stabilizing diet during the day, which includes monitoring carbohydrate amounts and quality, eating plenty of fiber, protein, and fat, and eating frequently enough to keep blood sugar stable.

Stabilizing your blood sugar through nutrition may help you gradually work toward comfortably fasting for 13 or more hours during the night.