In general, fasting refers to deliberately going without food for a period of time. Currently, it takes on several popular forms such as 16:8 (8-hour eating window and 16-hour fasting window), alternate-day fasting, 5:2 (5 days of regular eating with 2 days of limited calorie intake) and more.

Intermittent fasting may benefit anxiety, depression and mood in some cases. Research reviews from both Disease Markers and Nutrients highlighted a few clinical trials which showed that intermittent fasting led to improved vitality and reduced anxiety and depression.

There are a few possible reasons for this. For example, intermittent fasting switches the body over from glucose to fatty acid-derived ketone bodies for fuel, which may provide a steadier state of energy. Research has also shown that it improves insulin function which helps to stabilize blood sugar levels.

Second, fasting may increase brain-derived neurotrophic factor and neuroplasticity, as well as elevate key mood-boosting brain chemicals such as serotonin and endorphins. Together, these effects provide wide-reaching benefits for overall brain function and mental wellness.

Lastly, intermittent fasting may decrease inflammation in the brain and in the gut, the latter of which helps reestablish the important gut-brain connection.

Fasting may have certain pitfalls too. The same review in the Disease Markers journal analyzed a few clinical trials which showed an increase in depression, anxiety, irritability, fatigue and anger. One reason for this is that fasting increases the levels of stress hormones cortisol and adrenaline. Since many individuals with mental health issues already have high stress, increasing these hormones further may worsen psychological health symptoms.

Additionally, blood sugar drops during fasting, which can lead to irritability, anxiety, and other mood changes, especially for individuals who are sensitive to changes in blood sugar or hormonal changes in general.

Finally, fasting has been shown in some cases to actually decrease dopamine and other brain chemicals that play a role in motivation and mental well-being.

Overall, more research is needed to paint a definitive picture on the impacts of fasting and mental health. Given the potential benefits as well as possible drawbacks, one must exercise caution when implementing intermittent fasting. Since longer fasts are likely to lead to more pronounced changes, it is best to start small and work up from there if needed or desired.

Therefore, for individuals with anxiety and depression, it may be best to start with a less intense fasting schedule such as 12 hours on, 12 hours off, and adjust from there.