People report very different mood effects from intermittent fasting. Some say they feel steadier or more focused once they have adjusted; others find fasting makes them irritable, anxious, or low. Research on fasting and mood in humans is limited, mostly short-term, and often done in people without depression, so it cannot say who will benefit or be harmed.
This page explains the possible mechanisms, situations where caution is needed, practical points about psychiatric medication, and warning signs that mean you should stop. It is educational information only. Fasting is not a treatment for depression, anxiety, or any mental health condition, and should not replace care from a doctor or mental health professional.
If you are in crisis or having thoughts of harming yourself, contact your local emergency number or a crisis line in your country now. You do not need to wait until you are sure.
Table of Contents
Possible Mechanisms
Researchers have proposed several ways fasting might influence mood. Most are based on animal studies or small human studies, and none has been shown to make fasting an effective treatment for depression:
- BDNF (brain-derived neurotrophic factor). Fasting raises BDNF in animal studies. BDNF supports the growth and adaptability of nerve cells and has been linked to depression research, but human data on fasting and BDNF are limited and inconsistent.
- Ketones. During longer fasts the brain uses ketones (such as beta-hydroxybutyrate) for part of its energy. Some people describe a feeling of “clarity”; whether this relates to ketones is not established.
- Blood sugar. Some people notice energy dips after large, high-sugar meals. Eating fewer, more balanced meals may reduce these for some people.
- Inflammation. Inflammation is linked to depression in some people. Some fasting studies report lower inflammatory markers, but results are mixed and often tied to weight loss.
- Stress hormones. Fasting can raise noradrenaline and cortisol somewhat. This may feel like alertness to some people, but it can worsen anxiety or irritability in others.
- Fewer food decisions. Some people find a set eating window simplifies their day; others find it restrictive and stressful.
What People Report Feeling Better About
Some people say fasting helps with the following. These are self-reports and plausible explanations, not proven effects, and they do not mean fasting is suitable for anyone with a mental health condition:
- Fewer energy slumps after large meals
- Less grazing on ultra-processed snacks
- Better sleep after stopping late-night eating
- A sense of structure around meals
- Feeling better as a result of weight loss or improved fitness
Many of these benefits can also come from regular balanced meals, earlier dinners, and less processed food, without fasting. If you have depression or another mental health condition, talk to your healthcare provider before changing how you eat.
When Fasting May Worsen Mood
Fasting is more likely to be a problem, or should be avoided, in these situations:
- A current or past eating disorder; fasting can reinforce restriction and trigger relapse
- Moderate or severe depression, especially with low appetite, weight loss, or loss of pleasure in eating
- Anxiety that is triggered by hunger, shakiness, or body sensations
- High ongoing stress or poor sleep
- A recent bereavement, trauma, or major life upheaval
- Taking lithium or other medications affected by fluid, sodium, or food intake (see below)
- Anyone who notices a clear drop in mood when eating less
The First Few Weeks
Many people feel more irritable, tired, or low in the first week or two of a new fasting schedule. Hunger, changes in caffeine habits, fluid and sodium shifts, and disrupted sleep can all play a part. For some, this settles as they get used to the routine; for others it does not.
Mood is not something to push through. If your mood drops noticeably, you feel hopeless, or you are struggling to function, ease off or stop fasting and talk to your healthcare provider. A gentler schedule (such as a 12-hour overnight fast) or regular meals may suit you better.
Antidepressants and Other Psychiatric Medications
Talk to your prescriber or pharmacist before starting a fasting schedule if you take any psychiatric medication. Some general points to raise:
SSRIs and SNRIs (for example sertraline, escitalopram, fluoxetine, venlafaxine, duloxetine)
Some can cause nausea or stomach upset, which may be worse on an empty stomach. Your pharmacist can tell you whether yours is best taken with food and whether its timing can move to fit an eating window.
Tricyclics (for example amitriptyline, nortriptyline)
Often taken in the evening. They can cause dizziness on standing, which fasting may add to.
MAOIs (for example phenelzine, tranylcypromine)
These come with specific dietary restrictions (such as tyramine-containing foods) that still apply during eating windows. Any change to your eating pattern should be planned with your prescriber.
Lithium
Lithium levels are sensitive to fluid and sodium balance, and fasting affects both. Changes in intake can push levels too high, which can be dangerous. Do not start fasting while taking lithium without discussing it with your psychiatrist first; closer monitoring of blood levels may be needed.
Antipsychotics
Some antipsychotics affect appetite, weight, and blood sugar. If medication-related weight gain is a concern, discuss options with your prescriber rather than starting a fasting regimen on your own.
Don’t skip or move doses to fit your fasting schedule
Taking your medication consistently matters more than keeping a fast. If your medication is meant to be taken with breakfast, eat breakfast. Never stop or change psychiatric medication without medical advice.
Anxiety
Experiences with fasting and anxiety vary:
- Some people feel calmer with a predictable eating routine
- Others find that hunger, raised stress hormones, or extra caffeine make anxiety worse
- People prone to panic may find body sensations during fasting (lightheadedness, a racing heart) unsettling
- For people with health anxiety, tracking fasting hours and body signals can feed unhelpful monitoring
If anxiety is a concern, regular balanced meals, good sleep, and moderate caffeine are a sensible foundation. If you do try fasting, keep it gentle (for example 12:12) and stop if anxiety increases.
Bipolar Disorder
Bipolar disorder calls for particular care. Researchers are exploring links between metabolic health and bipolar disorder, but there is no established role for fasting in its management, and the risks are real:
- Sleep disruption, common when starting to fast, can trigger mood episodes
- Calorie restriction may destabilise mood
- Lithium levels can be affected by fasting (see above)
- Irregular eating can make mood changes harder to spot
Anyone with bipolar disorder should talk to their psychiatrist before trying any fasting schedule.
When to Stop
Stop fasting and speak to your healthcare provider if you notice:
- Low mood that is getting worse or not lifting
- New or worsening anxiety
- Sleep problems that do not improve
- Growing rigidity about food, guilt or distress when a fast is broken, or bingeing after fasts
- Loss of interest in food or eating, or unplanned weight loss
- Manic or hypomanic symptoms (for example much less need for sleep, racing thoughts)
- Thoughts of suicide or self-harm: seek help immediately through your local emergency number or a crisis line
Fasting is optional. If it is making life harder, particularly your mental health, stopping is the right choice.
Frequently Asked Questions
Can fasting treat depression?
No. There is not enough evidence to recommend fasting for depression, and for some people it may make things worse. Effective treatments such as talking therapies, medication, and other support are available through your doctor or a mental health professional.
Why do I feel mentally clearer when I fast?
Some people describe this, possibly because of steadier energy without large meals, a mild rise in alertness hormones, or simply fewer food decisions. It is a subjective experience, not a proven effect, and many people feel foggier instead.
Can I take my SSRI during my fasting window?
Many SSRIs can be taken with or without food, but check with your pharmacist or prescriber for your specific medication. If it upsets your stomach when taken fasted, taking it with a meal is usually the simple fix. Keep taking it at a consistent time.
I have a history of an eating disorder. Should I fast?
Generally no. Structured fasting can reinforce restriction and trigger relapse. Talk to your treating clinician before considering any change to your eating pattern.
Why am I more irritable when fasting?
Irritability is common when starting, often linked to hunger, sleep changes, caffeine, or low sodium. It may ease as you adjust, but if it persists or affects your relationships or work, fasting may not suit you.
Does fasting affect serotonin?
Possibly, in complex ways that are not well understood in humans. Popular claims that fasting “boosts serotonin” oversimplify limited research.
The Bottom Line
Fasting affects people’s mood in different ways, and the research is too limited to predict who will feel better or worse. It is not a treatment for depression or any mental health condition. People with an eating disorder history, moderate or severe depression, bipolar disorder, or those taking lithium should not fast without specialist advice. If you take psychiatric medication, check with your prescriber first and never skip doses to protect a fast. If your mood worsens, stop and seek support.