If you’ve ever forgotten to pack a granola bar for the day or maybe even (yes) fasted on purpose, you might recognize a weird feeling that creeps over you after going without a snack for longer than usual.
Is it giddiness? Elation? A little clarity? Well, it might be in your head. But there’s also some, albeit preliminary, science to suggest that you’re not imagining it — your fast may be altering your mood.
Certain forms of fasting — essentially abstaining from food intentionally — appear to have an effect on the mood, and have even been offered up as treatments for conditions that can cause depressive symptoms and a low mood.
More than ever, lifestyle enthusiasts everywhere are trying their hands (mouths?) at intermittent fasting. This is the practice of limiting eating by time — perhaps by restricting eating to a certain window of time during the day, or by eating every other day. Some proponents of the diet say it has a significant influence on their mood, which begs the question: Are they really experiencing a change in mood as a result of fasting, or are they riding high on a placebo effect?
“I’m convinced it could be useful in anxiety and depression,” Guillaume Fond tells Inverse. Fond is a psychiatrist who studies fasting and mood at Aix-Marseilles University in France.
But he also points out there is a serious lack of data to back up the hunch.
It’s safe to say that the science of the effects of fasting on mental health is very much in its infancy. But the research so far does hold some tantalizing clues to fasting’s influence on mood and mental health.
The science of fasting and mood
Studies of fasting — including intermittent fasting — and mood or mental health in humans tend to be hampered by several important factors, including small samples, unrepresentative participant populations, and poor study design. But by bearing these limitations in mind, scientists can use these preliminary results to open doors for new, more rigorous research.
These three studies are a case in point.
For example, in a 2018 study involving only people who all had multiple sclerosis, researchers created a diet regimen whereby some participants ate 22 percent fewer calories than usual every day of the week, while others practiced the 5:2 regimen. This is a kind of intermittent fasting in which people limit their calorie intake to 75 percent of baseline on two days of a week and eat whatever they want on the other five days. Both groups were then compared to a control group, who made no eating changes.
None of the participants’ MS symptoms considered in the study appeared to improve significantly, but the participants who dieted did see some other benefits.
On the measure of MS symptoms used in this study, the dieting participants’ emotional well-being went up. Compared to those who hadn’t made a diet change, those who restricted calories saw what the authors called a “clinically meaningful” improvement. But importantly, there was no clear difference between following a fasting diet or following a traditional calorie restriction diet every day.
In a different study from 2006, people with chronic pain who tried an 8-day prolonged fast also saw an improvement in their moods compared to those in a control group who followed a calorie-restricted diet. Curiously, the mood benefits only appeared in the latter half of the fast period.
More recently, a study from June of 2021 involving 22 adult women in Spain found that they reported improvements in depression symptoms following a time-restricted eating intervention where they ate early in the day. But there was no control group for this study, so it is hard to take the results at face value.
“Improvements in anxiety and depressive symptoms (increased energy, concentration) would be expected but there is no scientific evidence so far, unfortunately,” Fond points out.
What to make of mixed results
As with many things to do with fasting and health, there are some data that muddy the waters when it comes to how it affects mood — or not. For example, one study that involved around 30 men in 2013 found that a combination of fasting and calorie restriction decreased their feelings of tension, anger, confusion, and total mood disturbance relative to the control group, which made no changes — but their depression scores didn’t improve.
And in fact, there’s some evidence that suggests the opposite is true — fasting might negatively influence mood in some people. A 2002 study describes how people who had fatigue and pain followed a seven-day “fast” in which they ate 250 calories per day, and found it made no difference in their mood. Rather, some participants’ moods worsened.
And in another study from 2016, weightlifters who went on a 48-hour fast seemed to experience no difference in mood, except for anger levels, which worsened slightly.
When you eat might matter, too. One 2015 paper describes how women who ate breakfast before exercise in the morning appeared to have a better mood late in the day than did women who ate breakfast after exercise in the morning. This suggests that fasting in the early morning as part of time-restricted eating may not be good for mood.
The biology of fasting and mood
Only a handful of researchers have reviewed the scientific literature on fasting and mood or emotional well-being. One review from 2013 attempts to parse the biology that may be at play when it comes to mood changes and fasting. In this review, the researchers refer to studies involving therapeutic fasting, which mostly involve people with certain health conditions who abstain from food longer than a day or two.
One theory for fasting’s influence on mood is that during a fast, levels of certain hormones may shoot up or plunge down when a person stops eating for a prolonged period of time. This, in turn, could trigger a defense system of sorts in the brain.
In the body’s attempt to protect itself from the negative effects of higher than normal hormone levels, what the authors call “cellular mechanisms of stress resistance” may kick in.
They identify a number of chemical changes found in the brain when fasting:
- Levels of neurotransmitters (basically chemical messengers) norepinephrine, epinephrine, dopamine, and cortisol can increase.
- Tryptophan and serotonin may increase.
- There is an increase in brain-derived neurotrophic factor, which is a protein to do with nerve growth.
- Leptin and insulin levels may decrease.
- There may be decreased levels of thyroid hormones T3 and T4.
- Cerebral glucose — the sugar in your brain that it uses for energy — decreases.
- Endogenous endorphins may be released after a prolonged (5-10 day) fast.
- Production of ketone bodies, which may be involved in “improving mood, decreasing pain sensation, and promoting neuro-neuronal protection” in some cases.
What’s next — The human research may be thin, but there is more scientific data from studies of animals and intermittent fasting. From this research, scientists have gleaned evidence for fasting as a means of extending lifespan and even preventing diabetes, cancer, and cardiovascular disease. But studying mood disorders or the emotional wellbeing of mice in a lab presents obvious challenges. When attempting to translate such science to humans, that effect might magnify.
The human studies that do exist are a good start — but they are relatively small, short-term, and inconsistent.
But because mood disorders and depression are so hard to treat, more high-quality research in humans is badly needed. Psychiatric medication might not work in some cases, or might be unaffordable.
“I’m confident that fasting will emerge as a new therapeutic option in the next decade,” Fond says.
If there was a kind of fasting that could boost mood or relieve depression symptoms, it may present a low-cost way to lead a happier life.