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When you don’t eat for a long time, you may have problems when you do start to eat again. We call this the “refeeding response”.

What happens to my body when I don’t eat?

You get energy from the food you eat. Our bodies need enough energy to keep all our organs working well.

When you do not get enough energy for a long time, your whole body suffers. You lose weight, muscle mass, and strength. This affects all the organs in your body.

  • Your brain may not be able to think clearly causing brain fog.

  • Your intestines may not absorb food well causing you to feel bloated when you eat or drink.

  • Your blood system may not be able to adjust when going from sitting to standing without feeling dizzy.

  • Your heart rate may slow. Your heart muscle may weaken making it harder to pump blood. These problems lead to decreased blood supply to the rest of your body and can make you feel tired.

  • Your body may not control your body temperature well causing you to feel cold all the time.

  • Your immune system may not fight off disease causing you to get sick more often.

  • Your hormone levels may change, stopping your period and causing bone loss.

What is the refeeding response?

When you are not eating, you have less electrolytes in your body. Your body helps control these levels in the blood so that the heart and other organs will work well. Electrolytes include sodium, potassium, phosphorus, and magnesium.

Once you start to eat, these electrolytes move out of the blood and into the cells to make energy from the food we eat. If not enough remains in the blood, your heart and other organs will not work right. Your doctor will need to monitor your blood through lab tests to make sure you get more electrolytes if needed.

Is this safe?

The safest way to manage this response is in the hospital. Here, we can closely watch your electrolytes levels, and give you more, if needed.

If you cannot go to the hospital, there are ways to reduce your risk. Resume eating very slowly under the guidance of your doctor and registered dietitian.

Who to Call

If you are a UW Health patient and have more questions, please contact UW Health at one of the phone numbers listed below. You can also visit our website at www.uwhealth.org/nutrition.

Nutrition clinics for UW Hospital and Clinics (UWHC) and American Family Children’s Hospital (AFCH) can be reached at: (608) 890-5500.

Nutrition clinics for UW Medical Foundation (UWMF) can be reached at: (608) 287-2770.