What Are the Potential Side Effects and Disadvantages of Intermittent Fasting?

Intermittent fasting is an eating regimen that restricts the timing and sometimes the quantity of meals. Potential side effects and disadvantages include malnutrition, dehydration, hunger, and more.

Intermittent fasting has become popular as a dietary trend. It is associated with well-documented health benefits such as weight loss, decreased blood pressure, and decreased blood sugar levels, but its disadvantages are not widely known.

Read on to learn about intermittent fasting side effects, types, and more.

Intermittent fasting is an eating regimen that restricts the timing and sometimes the quantity of meals. The main goal is to prompt the body to enter ketosis, a state where it burns stored fat for fuel instead of dietary carbs.

The longer the fasting period, the longer the body maintains ketosis, resulting in increased fat burning and weight loss.

What are the types of intermittent fasting?

There are three popular types of intermittent fasting regimens:

• Alternate day fasting: Eat normally on one day but fast completely or eat a small, calorie-restricted meal (e.g., less than 500 calories) the next day.
• Daily time-restricted fasting: Fast for fixed periods during the day, like the 16:8 fast where you fast for 16 hours and eat all meals during an 8-hour window.
• Periodic fasting: Fast on specific days of the week. For example, eat normally from Monday to Friday and fast on weekends (Saturday to Sunday).

What are the side effects of intermittent fasting?

Here are the potential side effects:

Malnutrition

Prolonged or poorly planned calorie-restriction fasts can lead to malnutrition. Overeating to compensate for the nutrient deficit can be damaging.

Extreme calorie restriction is not sustainable in the long term, and it increases the risk of breaking the fast. Plan your fasting regimen to balance healthy, nutritious meals with fasting periods and avoid malnutrition.

During fasting, the body expels water and salt through urine, leading to dehydration. It is important to replace the lost water and salt during this period to prevent dehydration.

Additionally, not eating during fasting periods may cause dehydration. Stay hydrated and monitor your urine color regularly. Pale yellow is normal, while dark color may indicate dehydration.

Cravings and hunger

Increased hunger is common during the initial phase of fasting as the body adjusts to decreased calorie intake.

These symptoms usually clear up as the body adapts to regular and prolonged fasting.

During fasting, stored fats are used as fuel, and a byproduct called acetone can accumulate in the blood, causing discernible breath odor.

Lack of salivary flow during fasting can lead to increased acetone build-up in the breath, resulting in bad breath (halitosis).

Large water losses during the early days of fasting can cause dehydration, resulting in a dry mouth and worsened bad breath.

Digestion problems

Prolonged fasting and sudden dietary changes can negatively impact the digestive system, causing symptoms like diarrhea, constipation, nausea, and bloating.

Dehydration during intermittent fasting can worsen constipation. Staying hydrated and eating nutrient-rich foods is critical for maintaining good gastric health.

Headaches commonly occur during fasting, especially in the early days. They typically affect the front of the brain and are of mild to moderate intensity.

If you are prone to headaches, fasting, low blood sugar levels, and caffeine withdrawal (if abstaining from coffee) may trigger these headaches.

Moodiness and irritability

Low blood sugar levels resulting from reduced carb intake can cause irritability, stress, anxiety, and decreased concentration.

However, once you overcome moodiness and irritability, completing a fast can bring a sense of pride, satisfaction, and achievement.

Low blood sugar levels during fasting can cause tiredness or weakness. Sleep disturbances during fasting can also contribute to fatigue during the day.

These low energy levels usually improve after the initial fasting phase. Once the body enters ketosis and burns fat for fuel, you may feel energized. Regular fasting is unlikely to cause fatigue at this stage.

Sleep difficulties

Intermittent fasting can negatively affect sleep quality, leading to insomnia and disturbed sleep. Sleep disturbances are commonly reported during fasting.

The fatigue and dehydration caused by water and electrolyte loss in the early days of fasting may contribute to sleep disturbances.

Who should avoid intermittent fasting?

Although intermittent fasting has many beneficial effects, certain populations are at higher risk of experiencing harmful side effects. These populations include:

• Pregnant or breastfeeding women
• Children or teenagers
• Older adults with health conditions like chronic fatigue
• People with health conditions like eating disorders, nutritional deficiencies, dementia, traumatic brain injuries, or concussions
• People taking medications that aren’t suitable for fasting

If you experience intermittent fasting side effects like headaches, dizziness, nausea, irritability, unbearable hunger, or prolonged fatigue without resolution, consider stopping the fast and immediately contact your healthcare provider for guidance.

Unpleasant fasting experiences can be counterproductive. Focusing on nutritious meals, quality sleep, regular physical activity, and stress management may be preferable for recovery. Only fast when physically and mentally prepared.

QUESTION

American Journal of Clinical Nutrition: “Time-restricted feeding plus resistance training in active females: a randomized trial.”

Behavioral Sciences (Basel, Switzerland): “Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects-A Narrative Review of Human and Animal Evidence.”

BMC Complementary and Alternative Medicine: “Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting.”

Current Pain and Headache Reports: “Fasting headache.”

European Journal of Dentistry: “Halitosis: Current concepts on etiology, diagnosis and management.”

Frontiers in Nutrition: “Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis,” “The Psychological Effects of Short-Term Fasting in Healthy Women.”

John Hopkins Medicine: “Intermittent Fasting: What is it, and how does it work?”

Journal of Clinical & Translational Endocrinology: “Hypoglycemic symptoms in the absence of diabetes: Pilot evidence of clinical hypoglycemia in young women.”

Journal of the American College of Nutrition: “The Validity of Urine Color as a Hydration Biomarker within the General Adult Population and Athletes: A Systematic Review.”

Nutrients: “A Prospective Clinical Trial of Prolonged Fasting in Healthy Young Males and Females—Effect on Fatigue, Sleepiness, Mood and Body Composition,” “Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus.”

Nutrition & Diabetes: “Breath acetone as a marker of energy balance: an exploratory study in healthy humans.”

Nutrition, Metabolism, and Cardiovascular Diseases: “Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial.”

Obesity (Silver Spring): “Measuring breath acetone for monitoring fat loss: Review.”

PLOS ONE: “Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects.”

PLOS ONE: “Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects.”