Fasting and Heart Health: What the Science Says
Key takeaways
- A monthly 5-day fasting-mimicking diet improved some measures of heart function in people with type 2 diabetes in a year-long trial[1].
- The diet reduced left ventricular mass early on and improved diastolic function, the heart's ability to relax and fill with blood[1].
- Fasting may help the heart partly by improving blood sugar control, since better HbA1c was linked to better heart filling in the study[1].
- Fasting is not right for everyone, and people with diabetes or heart conditions should talk to a doctor before trying it.
What is fasting, exactly?
Fasting means going without food, or eating very little, for a set period of time.
There are many styles of fasting.
- Intermittent fasting, like eating only within an 8 to 10 hour window each day
- Alternate-day fasting, where you eat normally one day and very little the next
- Time-restricted eating, a milder form of daily fasting windows
- Fasting-mimicking diets, which use very low-calorie, plant-based meals for a few days to trigger fasting-like effects without full food restriction
A fasting-mimicking diet, or FMD, is designed to trick the body into a fasting state while still providing some nutrients.
This matters because full water-only fasting can be hard to sustain and risky for some people.
Why does fasting matter for the heart?
Heart disease is a leading cause of death in people with type 2 diabetes.
High blood sugar over time can stiffen the heart muscle and change its shape.
One of the earliest signs of heart trouble in diabetes is diastolic dysfunction.
This means the heart has trouble relaxing and filling with blood between beats, even before pumping strength (systolic function) declines.
Because diastolic problems often show up before other symptoms, researchers look closely at this stage to find ways to protect the heart early.
What does the research show?
A recent clinical trial looked at people with type 2 diabetes who followed a monthly 5-day fasting-mimicking diet for one year[1].
Researchers used detailed heart MRI scans to track changes in heart structure and function.
At 6 months, the fasting group showed a small drop in left ventricular mass, meaning the main pumping chamber of the heart became slightly smaller or thinner[1].
This effect faded by 12 months, so it may not be a lasting change.
More notably, the fasting group showed improved diastolic function at 12 months[1].
Two measures of how well the heart fills with blood, called E/A ratio and Ea velocity, both improved compared to usual care[1].
These improvements in heart filling were linked to better blood sugar control, measured by HbA1c, a marker of average blood sugar over about 3 months[1].
Interestingly, the heart benefit was also linked to changes in HDL cholesterol, sometimes called 'good cholesterol'[1].
This suggests fasting may help the heart partly through its effects on blood sugar and blood fat levels, not just weight loss.
How might fasting help the heart?
Scientists think fasting affects the body in several ways that could matter for heart health.
- Lowering insulin levels and improving insulin sensitivity, which reduces strain on blood vessels
- Reducing inflammation, which can damage the heart and arteries over time
- Promoting autophagy, a process where cells clear out damaged parts and recycle them
- Lowering blood pressure in some people
- Supporting modest weight loss, which reduces the heart's workload
In the trial above, better blood sugar control seemed to be a key link between fasting and improved heart filling[1].
This fits with broader nutrition science showing that chronic high blood sugar can stiffen heart tissue over time.
What should you actually do?
Fasting is not something to start without a plan, especially if you have diabetes or heart disease.
- Talk with a doctor before trying any fasting plan, especially if you take insulin or blood sugar medication
- Start gently, such as a 12-hour overnight fast, before trying longer windows
- Stay hydrated with water, and consider electrolytes during longer fasts
- Break a fast with a balanced meal that includes protein, fiber, and healthy fats rather than sugary foods
- Watch for symptoms like dizziness, shakiness, or extreme hunger, which can signal low blood sugar
- Pair fasting with other heart-healthy habits, like regular movement, sleep, and a diet rich in vegetables, whole grains, and fish
If you are curious about a structured fasting-mimicking diet, look for one designed and studied for safety, rather than an extreme homemade version.
People with diabetes should never skip prescribed medications without medical guidance, even during a fasting period.
Who might benefit most?
The trial discussed above focused on adults with type 2 diabetes, a group already at higher risk for heart problems[1].
People with insulin resistance or prediabetes may also be a group where fasting patterns are being studied for metabolic benefits.
Fasting is generally not recommended for certain groups.
- People who are pregnant or breastfeeding
- People with a history of eating disorders
- Children and teenagers still growing
- People with type 1 diabetes, unless closely supervised by a doctor
- People who are underweight or malnourished
What are the limits of the current evidence?
The trial on fasting-mimicking diets and heart MRI was relatively small, with 82 participants[1].
Some benefits, like the drop in heart mass, did not last through the full year, showing that timing matters when studying diet effects[1].
Longer studies with more people are needed to know if these heart changes reduce actual heart attacks or strokes over time.
Still, this study adds to a growing body of research suggesting fasting patterns can influence markers of heart health, not just body weight.
Frequently asked questions
Can fasting reverse heart damage from diabetes?
Some research suggests fasting patterns can improve markers of heart function, like how well the heart fills with blood, in people with type 2 diabetes[1]. This does not mean fasting reverses existing heart damage, and more research is needed.
Is intermittent fasting safe for people with diabetes?
It can be, but only under medical supervision, since fasting can affect blood sugar and medication needs. Anyone with diabetes should talk to a doctor before changing eating patterns.
How is a fasting-mimicking diet different from regular fasting?
A fasting-mimicking diet involves eating small, specific low-calorie meals for a few days instead of eating nothing. It is designed to create fasting-like effects in the body while still providing some nutrition.
Put this to work in your own food log. Track it free with Ration →
