Short answer: donating blood does burn a small number of calories and causes a temporary reduction in iron stores; however, the evidence that donation meaningfully lowers cholesterol or substantially reduces heart attack risk is mixed and not definitive. Below is a summary of findings and cautious interpretation.
Calories burned
Donating blood requires your body to replace the fluid and cells removed. The metabolic effort to make new red blood cells consumes energy — some studies estimate the caloric cost of producing the donated blood is modest (a few hundred calories) but this should not be relied on as a weight-loss strategy.
Cholesterol and iron
Donors lose some iron with each donation. Some research shows associations between lower iron stores and improved cardiovascular markers in certain populations, but findings are inconsistent. Donating blood should not replace medical treatment for high cholesterol.
Heart attack risk
Observational studies have sometimes reported lower cardiovascular disease in groups of donors versus non-donors, but these studies can be affected by 'healthy donor' biases: people who donate are often healthier to begin with. Randomized evidence is lacking, so claims that donation directly reduces heart attack risk are not proven.
Practical advice
- Donating blood can be part of a healthy lifestyle but should not be used as a medical intervention for cholesterol or heart disease prevention.
- Discuss iron status with your doctor if you donate regularly; some donors benefit from dietary advice or supplements.