Intermittent fasting is a populardiet trend, with some evidence it can boost metabolism.- But be wary of
fasting if you have a history of disordered eating or are trying to gain muscle. - Fatigue and dizziness, losing sleep, or missing a period are signs that you should stop fasting.
Intermittent fasting, or limiting your eating to a set window of time each day (or week), is one of the biggest trends in
But it's far from a cure-all for any of these issues, and there are still limitations to the research showing its benefits for humans, experts say.
Abstaining from food - even for short periods - can also have side effects. You may want to be wary of intermittent fasting if:
You have a history of disordered eating
Intentionally restricting food during certain hours of the day or certain days of the week can be a major trigger for disordered eating, Christy Harrison, an anti-diet registered dietitian who hosts the Food Psych podcast, previously told Insider.
Trying to abstain from eating when you're hungry teaches you to ignore your body's natural cues, which can set a dangerous precedent, particularly for those with an already fraught relationship to food, according to Harrison.
"I can't tell you how many people have binge eating or emotional eating flare up because of intermittent fasting," she said.
If you've previously struggled with any kind of disordered eating, it's a good idea to consult an expert before fasting of any kind.
You lose your period
Another possible side effect of intermittent fasting can occur if you're restricting calorie intake too much, depriving your body of energy it needs to function normally.
For people who typically have monthly menstrual periods, a disruption to your cycle is an obvious symptom.
Losing your period is a major sign that your body is trying to conserve energy and you should stop fasting, according to Dr. Caroline Apovian, co-director of the Center for Weight Management and Wellness at Brigham and Women's Hospital.
You experience fatigue, nausea, or dizziness
If you start to feel tired all the time, nauseous, dizzy, or lightheaded, it could mean you're not eating enough, Apovian previously told Insider.
While it's normal to have some adjustment period when trying a new diet, experiencing these symptoms for more than a week or two can be a sign that your body isn't adapting well to intermittent fasting and you should seek medical advice.
And if any of the symptoms are severe, you should stop fasting immediately. Riskier side effects such as fainting or changes in blood pressure sometimes occur with more extreme forms of fasting.
You're losing sleep
Another sign that fasting is taking a toll on your health is disrupted sleep. You may have trouble falling asleep at night or be unable to stay asleep consistently. This might be accompanied by feelings of hunger but can also happen if you're not aware of being hungry too.
Research has suggested that intermittent fasting might affect your circadian rhythm, and potentially decrease your deep REM sleep as a result.
Poor sleep could also be related to increased levels of cortisol, a stress hormone produced by the body, which can be exacerbated by a new fasting routine.
In either case, if intermittent fasting is stopping you from getting quality shut-eye, it might be best to have a bedtime snack, recommends Dave Asprey, CEO of the health and performance company Bulletproof and author of a new book on fasting.
You're trying to gain or maintain muscle
While intermittent fasting is often used to boost weight loss, it could backfire for athletes and exercise enthusiasts, particularly those trying to get stronger.
Research has shown intermittent fasting may make you more likely to lose muscle mass, compared to other types of weight loss diets.
Skipping meals can also make it hard to stay in a calorie surplus (eating more than you burn off) which is necessary for building muscle, particularly if you're also exercising intensely and often.