Is it true that intermittent fasting causes extreme fatigue? This is a question many people wonder about, especially when deciding whether to practice intermittent fasting. Concerns about energy levels are common, with some fearing that this eating pattern might leave them feeling completely exhausted.
Let’s take a closer look at the truth behind these concerns and what really happens when you practice intermittent fasting.
The Basics Of Intermittent Fasting
Intermittent fasting breaks away from the typical pattern of eating several times a day. Instead, it involves eating during specific times and fasting during others, which can help your body function more efficiently and support health benefits like better blood sugar control and reduced inflammation1.
One reason people are attracted to intermittent fasting is that it mirrors a more natural eating pattern, similar to how our ancestors might have eaten when food wasn’t always readily available. This approach gives your body a break from continuous digestion, which can enhance fat burning and help manage body weight. Fasting allows your body to focus on burning fat instead of processing food constantly, potentially supporting weight loss and contributing to improved health2.
Intermittent fasting also appeals to many because it simplifies eating habits. You don’t need to constantly count calories or follow strict diets. Instead, you focus on eating within a certain time frame, which can make it easier to manage what and how much you eat. For some, this approach feels more manageable and less restrictive than traditional diets.
The interest in intermittent fasting also comes from studies suggesting it might support processes like cellular repair and possibly even extend life expectancy3. While it’s not suitable for everyone, the combination of historical eating patterns and scientific research makes intermittent fasting a practical and appealing option for many people.
Understanding Intermittent Fasting Fatigue
Intermittent fasting is popular for its simplicity and potential benefits, but it’s important to be aware of some possible downsides. One common issue people encounter is fatigue.
When you start intermittent fasting, your body may need time to adjust to the new eating pattern. This adjustment period can lead to feelings of tiredness or low energy, especially if you’re used to eating frequently. Your body is adapting to a new routine where it has to operate on fewer fuel sources during the fasting periods, which can sometimes result in decreased energy levels.
Causes Of Fatigue During Intermittent Fasting
Fatigue during intermittent fasting can be influenced by several important factors. One of the primary causes is low blood sugar. When you fast, especially for extended periods, your body uses up the glucose stored in your liver and muscles for energy. As these stores get depleted, your blood sugar levels drop, which can cause symptoms like sweating, dizziness, and blurred vision4. This effect is more pronounced if your diet during the eating periods doesn’t provide enough carbohydrates to replenish your glucose levels.
Dehydration is another significant factor contributing to fatigue during intermittent fasting. Fasting can sometimes lead to reduced fluid intake, especially if you’re not consciously drinking water or other hydrating beverages. The body relies on adequate hydration to maintain energy levels, support metabolism, and regulate body temperature. Even mild dehydration can cause fatigue, headaches, and lightheadedness, which are common complaints among those new to fasting5.
Nutrient deficiencies are also a key cause of fatigue in intermittent fasting. If your meals aren’t balanced or varied enough, you might not be getting sufficient amounts of essential nutrients like iron, magnesium, and B vitamins. These nutrients play a critical role in energy production, oxygen transport, and muscle function. For instance, a deficiency in iron can lead to anemia, which is characterized by chronic fatigue and weakness. Similarly, a lack of magnesium can affect muscle relaxation and energy metabolism, contributing to tiredness6,7.
Inadequate caloric intake is another factor that can lead to fatigue8. If you’re not eating enough calories during your eating windows, your body might not have the energy reserves it needs to function optimally throughout the day. This can be particularly challenging for those who combine intermittent fasting with a calorie-restricted diet, as the combination can result in an energy deficit. Over time, this can cause persistent fatigue, making it difficult to maintain regular daily activities.
Sleep disruption is also a noteworthy cause of fatigue during intermittent fasting9. Changing your eating schedule can sometimes interfere with your natural sleep patterns. For example, if you’re eating too close to bedtime or fasting during times when you previously ate, it can affect your sleep quality. Poor sleep or insufficient rest not only directly causes fatigue but can also contribute to other factors mentioned, creating a cycle of tiredness and low energy.
Mental health conditions, such as anxiety and depression, can increase fatigue during intermittent fasting10. These conditions can impact energy levels and motivation, making it harder to cope with the physical demands of fasting. Anxiety, for instance, can lead to restlessness and poor sleep, while depression can cause chronic fatigue and a lack of interest in daily activities. Fasting might also trigger or worsen these symptoms, particularly if it leads to significant changes in routine or eating habits. For those with a history of eating disorders, intermittent fasting can be especially risky, as it may trigger unhealthy behaviors or worsen mental health symptoms.
Addressing these factors involves making thoughtful adjustments to your fasting routine. Ensuring that your meals are nutrient-dense and balanced, drinking plenty of water throughout the day, consuming enough calories to meet your body’s energy needs, and maintaining good sleep hygiene can all help in managing and reducing fatigue. If fatigue persists, it’s important to consider whether intermittent fasting is the right approach for you and consult with a healthcare professional if needed.
Is It True That Intermittent Fasting Causes Extreme Fatigue?
Intermittent fasting typically does not cause extreme fatigue for most people. Some individuals might experience mild tiredness when they first start fasting, but this often improves as the body adjusts to the new eating pattern.
Research has shown that certain intermittent fasting methods, like the 16:8 approach, can actually reduce both physical and mental fatigue. This makes it a beneficial option for people in demanding jobs, such as shift workers or those with physically active roles. Additionally, studies suggest that intermittent fasting might be helpful for those managing chronic conditions or undergoing treatments like chemotherapy, as it has been found to decrease a marker associated with tumor growth11,12.
Interestingly, a study on rats found that those on an intermittent fasting regimen gained weight more slowly, had lower blood glucose levels, and higher ketone levels compared to those with unrestricted food access. Ketones are produced by the liver when your body breaks down fat for energy instead of relying on glucose. These higher ketone levels were associated with less fatigue and improved physical and mental energy13.
Although the study was conducted on rats, it offers promising insights into the effects of intermittent fasting. So, while there might be a period of adjustment, intermittent fasting could actually help you feel more energized in the long run.
Who Should Avoid Intermittent Fasting?
Intermittent fasting isn’t suitable for everyone, and certain groups of people should avoid it due to potential risks and complications. Here are some groups who should be cautious or avoid intermittent fasting altogether:
People with Eating Disorders or a History of Eating Disorders
Those with conditions like anorexia, bulimia, or binge eating disorder should avoid intermittent fasting. The restrictive nature of fasting can trigger disordered eating behaviors, worsen symptoms, and lead to unhealthy patterns of food restriction and obsession with eating schedules.
Individuals with Chronic Health Conditions
People with chronic conditions such as diabetes, especially those who take insulin or other medications that lower blood sugar, should be cautious. Fasting can lead to dangerously low blood sugar levels (hypoglycemia) or other complications. Similarly, those with conditions like heart disease, kidney disease, or gastrointestinal disorders should consult with a healthcare provider before attempting intermittent fasting, as it may worsen their condition.
Pregnant or Breastfeeding Women
Pregnant women and those who are breastfeeding have increased nutritional needs to support their baby’s development and milk production. Fasting can restrict essential nutrients and calories needed during these stages, potentially affecting both mother and baby.
Children and Adolescents
Young people are still growing and developing, requiring a steady intake of nutrients and calories. Intermittent fasting can interfere with this process and may lead to nutrient deficiencies, delayed growth, and other health issues. It’s generally advised that children and teenagers avoid fasting unless under medical supervision for specific conditions.
People with a History of Mental Health Conditions
Individuals with conditions like anxiety or depression should be cautious with intermittent fasting. The restrictive nature of fasting can sometimes worsen mood disorders, increase anxiety levels, or contribute to feelings of fatigue and irritability. It’s important for those with mental health conditions to monitor how fasting affects their mood and overall mental state.
Those with a High Physical Activity Level
Athletes or individuals with highly demanding physical jobs might find it challenging to meet their energy needs while fasting. Insufficient calorie intake can lead to reduced performance, fatigue, and even muscle loss. For those who engage in high-intensity workouts, intermittent fasting might not provide the necessary fuel for optimal performance.
People with a History of Hypoglycemia
Those prone to hypoglycemia or low blood sugar should avoid intermittent fasting as it can trigger episodes of low blood sugar, leading to dizziness, confusion, fainting, and other serious health issues.
Individuals on Certain Medications
Some medications need to be taken with food or at specific times throughout the day. Fasting might interfere with the effectiveness of these medications or lead to side effects. People on medications, especially those for chronic conditions, should consult their healthcare provider before starting intermittent fasting.
Managing Fatigue During The Fasting Period
Managing fatigue during fasting can be a lot easier with the right approach, helping you feel more energized and comfortable throughout the fast. Here are some tips to keep in mind:
Keep Hydrated. Staying hydrated is one of the simplest ways to combat fatigue while fasting. Drinking plenty of water is key, but you can also enjoy herbal teas or black coffee if you like. These can help keep your energy up without breaking your fast. Hydration is crucial for keeping your body running smoothly and avoiding that sluggish feeling that can come with dehydration.
Watch for Electrolyte Imbalance. Along with water, it’s important to keep your electrolytes in check. Minerals like sodium, potassium, and magnesium help your muscles and nerves work properly. If you start feeling a bit tired, try adding a small pinch of salt to your water or sip on an electrolyte-enhanced beverage (without sugar). This is especially helpful during longer fasting periods when your electrolyte levels might dip, causing fatigue.
Manage Stress. Stress can take a toll on your energy levels, especially when you’re fasting. High stress can leave you feeling drained, so finding ways to relax is really important. Simple things like deep breathing, meditation, or even a gentle walk can help lower stress and keep your energy steady. Keeping stress under control also helps avoid emotional eating, which can affect how you feel during fasting.
Prioritize Good Sleep. Getting enough sleep is vital for managing fatigue. Fasting can sometimes mess with your sleep schedule, so try to stick to a regular bedtime and create a calming evening routine. Aim for a good 7-9 hours of sleep each night. If fasting late is disrupting your sleep, consider shifting your eating window earlier. Good sleep will help you wake up refreshed and better able to manage your fasting day.
Stay Active—Gently. Light physical activity, like a short walk or some stretching, can actually help boost your energy during fasting. Moving around gets your blood flowing and can lift your mood, making you feel more energized. Just be mindful not to overdo it, especially during longer fasts, as too much exercise can leave you feeling more tired.
Focus on Balanced Meals. What you eat during your eating window has a big impact on how you feel during your fasting period. Try to eat balanced, nutrient-rich meals that include a good mix of complex carbs, healthy fats, and proteins. These foods provide a steady release of energy, helping you avoid the ups and downs that can lead to fatigue.
Final Thoughts
While some individuals may initially experience fatigue when starting intermittent fasting, it’s not necessarily a given for everyone. As your body adjusts to this new eating pattern, you may find that your energy levels stabilize and even improve. Time-restricted eating, such as the 16:8 method, can help regulate your food intake and support more consistent energy throughout the day.
If you do experience significant fatigue, it might be helpful to fine-tune your approach to intermittent fasting. For example, you could try adjusting the duration of your fasting or eating windows to see what works best for your energy levels. Ensuring that your meals during the eating period are rich in nutrients—like proteins, healthy fats, and complex carbohydrates—can also make a difference in maintaining steady energy throughout the day.
If fatigue persists, it might be worth experimenting with different fasting methods or seeking guidance from a healthcare professional. They can offer tailored advice and help address any specific concerns or underlying health conditions that could be affecting your energy.
