The Effects of Not Eating

Periods of fasting have long been part of many religious, traditional, and cultural practices, but in recent years, the idea has become more widely adopted and used not as a spiritual tool but as a way to control diet and lose weight.

Author | Bridget Clerkin

7 sources cited

Effects of not eating

When used for these “health-based” reasons, however, and especially when practiced for extended periods of time, the concept of fasting or intermittent fasting remains controversial from a medical standpoint, as it can have several deeper impacts on mental, physical, and emotional health.

Health Effects of Not Eating

Intermittent fasting can be practiced in several ways, including limiting calorie intake to several hours a day or fasting completely on alternate days. [1] While the practice has been found to have some benefits, including lower LDL cholesterol levels, other studies worry these results are untested or under-tested in humans, making the health claims of intermittent fasting misleading. [1,2]

Not eating altogether for an extended period can have severe effects on both your mind and body.

Not eating altogether or practicing extreme caloric restriction is a different and more severe approach. This type of fasting, especially when practiced for extended periods of time, such as not eating for a week, can have a number of dangerous effects on the mind and body.

Physical Effects of Not Eating

Food is essential to the human body, providing it with the energy it needs to function properly and thrive. When the body is deprived of enough food, it looks elsewhere for energy sources, including its own tissues. [3]

Fat stores are tapped first, but once these are depleted, the body will move on to other areas, including muscle, skin, hair, and nails, for essential nutrients. The result can be possible hair loss, brittle hair, skin problems, and muscle wasting, among other issues. [3]

Eventually, the body will also begin shutting down internal systems to conserve energy, which can cause a cascade of health problems, including: [3,4]

  • Immune system issues, including healing from sickness and physical wounds
  • Low heart rate
  • Abnormal blood pressure
  • Low body temperature
  • Issues with digestion
  • Stunted growth, especially in younger people
  • Higher resting metabolism rate (which can increase the amount of fat the body holds on to)

On top of not eating enough calories, someone who does not eat may face issues related to nutritional deficiencies, including: [3]

  • Anemia
  • Weakness and fatigue
  • Vision problems
  • Soft bones

Mental and Emotional Effects of Not Eating

Not eating enough is not only linked to physical health. It can have several impacts on someone’s mental state.

Anxiety, anger, irritability, fatigue, and tension have all been linked to fasting, even after short periods. [1] Low glucose (sugar) levels specifically were tied to several mental difficulties, including confusion, amnesia, and “weird thinking.” [1]

Low blood sugar is also being increasingly connected to emotion regulation issues, with some studies showing people with low glucose levels being more prone to developing anxiety and depression disorders. [1]

Undernutrition can lead to both physical and mental health conditions.

Undernutrition has also been linked to elevated levels of cortisol, the hormone produced by the body when experiencing stress. [4] While this can bring on many physical complications, it’s also linked to some mental health issues, including depression. [5]

When Not Eating May Be an Eating Disorder

When used as part of cultural or religious observances for a designated period of time, calorie restriction and other forms of fasting may be practiced safely. However, it’s easy for this behavior to get out of control, to the point of becoming unhealthy and unhelpful, especially when used for dieting or weight concerns.

A major marker of most eating disorders is a fixation on food, eating, and body image. If someone practices fasting due to these concerns or continues fasting due to increasing concerns about what they eat or their appearance, it could be a sign that they’re developing an eating disorder.

Eating disorders like anorexia nervosa are also maintained by an extreme fear of gaining weight and are characterized by persistent behavior that interferes with weight gain. [6] When not eating or fasting is used in this way, or for this reason, it could point to a larger problem.

Overall, if someone is fasting or not eating to intentionally get an inadequate calorie intake, lose weight, and control their food consumption, it could mean that their eating habits have become concerning and potentially problematic.

How to Find Help for an Eating Disorder

Thankfully, there are many ways to find help for eating disorders or even dangerous eating behaviors that may not necessarily yet be part of a full-blown eating disorder, such as regular fasting.

Interventions like nutritional counseling, medication, and medical check-ins can help someone regain a healthy weight, while individual or group therapy sessions can help address underlying mental health issues that may be in play.

Your primary care physician or therapist can be a good place to start looking for help. These experts can point you in the direction of programs or even give you or your loved one an official diagnosis, which is often the first step toward entering eating disorder treatment.


Yes. Low blood sugar and other complications caused by drastic calorie restriction can lead to headaches, among other cognitive issues. [1]

It’s possible. The hydrochloric acid in an empty stomach may slosh around and hit the lower esophageal sphincter, which also happens when you throw up. The sensation can stimulate feelings of nausea and possibly cause you to throw up. [7]

Yes. Not eating nearly always leads to low blood sugar, though blood sugar levels can also rise to dangerous levels once eating resumes. [3]


  1. Wang Y, & Wu R. (2022). The Effect of Fasting on Human Metabolism and Psychological Health. Disease markers; 2022:5653739.
  2. Lowe D, Wu N, Rohdin-Bibby L. (2020). Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity. JAMA Internal Medicine; 180(11):1491-1499.
  3. Malnutrition. (n.d.). Cleveland Clinic. Accessed November 2023.
  4. Martins VJ, Toledo Florêncio TM, Grillo LP, do Carmo P Franco M, Martins PA, Clemente AP, Santos CD, de Fatima A Vieira M, & Sawaya AL. (2011). Long-lasting effects of undernutrition. International journal of environmental research and public health; 8(6):1817–1846.
  5. Dziurkowska E, & Wesolowski M. (2021). Cortisol as a Biomarker of Mental Disorder Severity. Journal of Clinical Medicine; 10(21):5204.
  6. DSM-IV to DSM-5 Anorexia Nervosa Comparison. (n.d.). Substance Abuse and Mental Health Services Administration. Accessed November 2023.
  7. Villazon L. (n.d.). Why do I feel sick when I’m hungry? BBC. Accessed November 2023.

Last Update | 12 - 7 - 2023

Medical Disclaimer

Any information provided on the is for educational purposes only. The information on this site should not substitute for professional medical advice. Please consult with a medical professional if you are seeking medical advice, a diagnosis or any treatment solutions. is not liable for any issues associated with acting upon any information on this site.