Alternate-Day Fasting: Everything You Need to Know

In the ever-evolving dietary trends, alternate-day fasting (ADF) has emerged as a compelling approach beyond traditional calorie restriction. If you’re someone who wants to venture into ADF as a diet approach, you’re on the right page.

This article aims to provide a comprehensive guide to alternate-day fasting, exploring its intricacies, benefits, potential drawbacks, and safety considerations. Focusing on scientific detail and credibility, we get into key subtopics to equip you with a thorough understanding of this fasting method.

Key Takeaways:

  • During alternate-day fasting, you fast one day and eat regularly the other day.
  • It improves weight loss, inflammatory markers, and heart health.
  • When starting ADF, you might experience hunger and digestive changes.

Table of Contents:

What Is Alternate-Day Fasting?

Alternate-day fasting involves alternating between regular days and fasting days.

Some people also call it the“feast and fast diet.”

In this type of intermittent fasting, individuals either refrain from calorie intake entirely or consume a limited amount during fasting days.

Here’s a quick overview of the two types of alternate-day fasting:

Complete Alternate-Day Fasting (ADF):

  • Approach: This variant involves a full day of fasting alternated with days of regular eating.
  • Fasting Days: On fasting days, individuals abstain from calorie intake entirely, relying on water, black coffee, unsweetened tea, and other non-caloric beverages.

Modified Alternate-Day Fasting (mADF):

  • Approach: In mADF, individuals alternate between regular eating days and modified fasting days.
  • Fasting Days: On modified fasting days, individuals can consume a limited amount of calories, typically around 500 or 25% of daily energy needs, preferably eaten once at lunchtime.

Does Alternate-Day Fasting Work for Weight Loss?

Scientific data suggests that alternate-day fasting is an effective way to lose weight. The underlying principle is creating a calorie deficit over time, promoting moderate weight loss without continuous caloric restriction.

Studies suggest that ADF can result in 3% to 7% reductions in body weight1 in as early as 6 to 12 weeks, with improvements in lipid profiles, blood pressure, and insulin sensitivity. Network analysis of a combined data set indicated that time-restricted eating, calorie energy restriction, and alternate-day fasting/modified ADF ranked top2 in terms of effectiveness for weight reduction.

Additionally, combining ADF with a low-carbohydrate diet may enhance weight loss further. Importantly, ADF has shown effectiveness in reducing harmful visceral fat3, particularly around the abdominal area, which is associated with increased health risks.

Fat loss makes up the majority of weight reduction with intermittent fasting diets, including ADF. According to a 2011 research,4 fat reduction notably accounted for 79% of weight loss (level I evidence).

During the follow-up period following the intervention, the participants regained some weight; nonetheless, their average body weight remained much lower than their baseline values. This implies that keeping watch of your daily calorie intake is still essential even after losing weight following ADF.

woman drinking water on alternate-day fasting

Alternate-Day Fasting, Hunger, and Cravings

Studies examining the effects of ADF on hunger have produced mixed findings. Some suggest that hunger eventually diminishes5 on fasting days, while others report no significant change.6 However, it’s crucial to differentiate between full fasting days and modified ADF, where you are permitted a reduced calorie intake (around 500 calories) on fasting days.

Research indicates that modified ADF, particularly with 500 calories on fasting days, is more tolerable than complete fasts.6 Participants reported more manageable hunger levels during modified ADF.

Regarding hunger hormones, studies suggest no increases in ghrelin levels6 from the baseline during alternate fasting days, with a decrease in fasting insulin levels.

Does Alternate-Day Fasting Induce Starvation Mode?

Contrary to misconceptions, ADF does not seem to induce the so-called “starvation mode” to the same extent as continuous caloric restriction.

Most weight loss approaches result in a minor decline in resting metabolic rate, commonly known as entering a state referred to as “starvation mode,” scientifically termed adaptive thermogenesis.

In response to severe calorie restriction, starvation mode occurs when the body conserves energy by diminishing the calories it expends. Consequently, weight loss may stagnate, and individuals might experience a sense of misery.

Remarkably, ADF appears to deviate from this pattern. An 8-week study7 comparing the impact of traditional calorie restriction and ADF revealed that continuous calorie restriction led to a noteworthy 6% reduction in resting metabolic rate concerning lean mass.

In contrast, ADF induced only a marginal 1% decrease. Notably, following 24 unsupervised weeks, the calorie-restricted group sustained a 4.5% lower resting metabolic rate from the study’s commencement. In contrast, ADF participants encountered a mere 1.8% reduction. This implies that ADF may not induce the same magnitude of metabolic rate decline as continuous calorie restriction.

Benefits of Alternate-Day Fasting

While ADF became famous for its weight loss effects, it offers other health benefits. In this section, we will give a thorough discussion on scientifically-backed benefits.

Glucose Regulation and Insulin Sensitivity

Numerous studies have investigated the effects of ADF on glucose metabolism and insulin sensitivity. While some research suggests minimal effects on fasting glucose8 and hemoglobin A1c (HbA1c) levels, consistent findings indicate a substantial reduction in fasting insulin9 and HOMA-IR, a metric for insulin resistance.

Notably, these improvements are more pronounced in individuals with higher baseline levels of insulin resistance, positioning ADF as a potent strategy for addressing metabolic abnormalities.

Lipid Profiles and Cardiovascular Health

Cardiovascular health represents a vital facet of metabolic well-being, and ADF has demonstrated favorable impacts on various lipid markers. Studies consistently report reductions10 in total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides,11, and systolic and diastolic blood pressure.12

Moreover, the modulation of LDL particle size,13 with an increase in larger particles associated with lower coronary heart disease risk, underscores the potential cardiovascular benefits of ADF. This multifaceted improvement in lipid profiles aligns with broader cardiovascular risk reduction, highlighting ADF’s potential for weight management and overall cardiovascular health.

Inflammatory and Oxidative Stress Markers

Beyond traditional metabolic parameters, experts investigate ADF for its effects on inflammatory and oxidative stress markers. Studies suggest reduced C-reactive protein levels14 after weight loss, indicating a potential anti-inflammatory effect.

This anti-inflammatory impact is particularly relevant given the established link between chronic inflammation and metabolic disorders. However, this claim still needs more long-term clinical studies due to conflicting results on data gathered.

Stimulation of Autophagy

The stimulation of autophagy is a pivotal mechanism through which ADF is believed to confer cellular benefits, contributing to cellular rejuvenation, longevity, and the prevention of various diseases.

Research indicates fasting induces autophagy,15 acting as a form of cellular cleansing. This process involves the removal of damaged or dysfunctional cellular components, including organelles and proteins, promoting cellular homeostasis. By clearing out these cellular “debris,” autophagy plays a crucial role in maintaining cellular integrity and function.

Animal studies16 have consistently demonstrated a link between fasting, autophagy stimulation, and increased lifespan. Autophagy contributes to the reduction of oxidative stress,17 a critical factor in aging and the pathogenesis of various diseases, including neurodegenerative disorders and cancer.

ADF’s ability to stimulate autophagy aligns with its potential to mitigate oxidative damage and prevent diseases associated with aging and cellular dysfunction.

Alternate-Day Fasting Side Effects

Hunger and Irritability

During the initial phases of ADF, individuals may experience increased hunger, accompanied by mild irritability. Scientific studies suggest that these symptoms are common but diminish as the body adapts to the fasting routine.5

On a good note, participants of short-term intermittent fasting show positive affective experiences of increased sense of achievement, reward, pride, and control18 despite the increased irritability and hunger. There was also no report of significant changes in overall mood.

Occasional Sleep Problems

Some individuals may encounter mild disruptions in sleep patterns when fasting, especially those following a strict decrease in calorie intake. In a 2019 study of 1422 subjects under a rigid 4 to 21-day fasting period,19 14.94% of the participants reported sleep disturbances, the most frequent mild symptom.

However, research on ADF indicates that these issues are often transient and improve with continued adherence to the fasting schedule. Some studies support that ADF does not diminish the sleep quality among its participants. In a 2021 research,20 experts examined 31 obese individuals who fasted every other day and followed a low-carb diet for six months. The study discovered that this regimen impacted neither the length nor the intensity of insomnia.

Digestive Changes

A potential side effect of ADF is constipation.21 Ensuring an adequate intake of fiber-rich foods on non-fasting days and staying hydrated can mitigate this issue. Studies propose that increased fiber consumption positively influences digestive health.

An animal study among obese mice states that a combination of functional fiber and ADF increased Lactobacillus, Bifidobacterium, and S24-722 in the intestine, with a decrease in adiposity and insulin resistance. This indicates the importance of increasing fiber intake during ADF to avoid constipation and improve overall gut health.

Physiological Responses

ADF may lead to occasional sensations of dizziness and weakness,11 especially during the initial adaptation phase, where the body adapts to the decrease in glucose intake. These symptoms are generally mild and temporary. It is essential to stay well-hydrated and incorporate nutrient-dense foods on feasting days to help alleviate these effects.

Not Suitable for Certain Populations

  • Pregnant and Breastfeeding Women: ADF is generally discouraged for pregnant and breastfeeding women due to increased nutritional demands during these periods.
  • Children: Given their growth and development needs, children are not considered suitable candidates for ADF.
  • Individuals with Eating Disorders: ADF may not be suitable for individuals with a history of eating disorders, such as anorexia nervosa or bulimia. While there are studies to support that ADF decreases the potential for eating disorders, it is still essential to consult your physician before doing so.

Note that responses to alternate-day fasting can vary based on age, gender, baseline health status, and other factors.

Is Alternate-Day Fasting Healthy When You Have Normal Weight?

ADF is not exclusive to weight loss; it offers health benefits for individuals with average weight. ADF provides a unique avenue to foster overall well-being for individuals within a normal weight range. Scientific literature shows the potential health implications of ADF in this demographic.

ADF enhances metabolic flexibility in those with non-obese individuals,6 promoting efficient switching between glucose utilization and fat burning. This adaptive response increases reliance on fat stores for energy during fasting, potentially influencing long-term metabolic health.

The study also suggests that people with average weight should opt for a modified ADF approach and add one small meal on fasting days to decrease hunger.

People within the normal weight range but have high blood pressure may also benefit from ADF. A 2020 study showed that one month of alternate-day fasting effectively lowers blood pressure and heart rate23 in healthy nonobese humans, suggesting that chronic fasting may enhance parasympathetic activity.

However, ADF, especially complete ADF, provides fewer calories than needed to maintain weight, making it more suitable for those looking to lose weight or fat mass.

Is Alternate Day Fasting Safe?

Rigorous scientific scrutiny affirms the safety of ADF for a broad demographic, excluding specific groups like children, pregnant or lactating women, and those with certain medical conditions. Long-term studies on individuals practicing ADF for over six months reveal no detrimental effects on bone mass,24 and there is a lack of evidence for other long-term side effects.

Commonly reported side effects during ADF initiation include mild symptoms such as hunger, irritability, occasional sleep disturbances, and dizziness. Significantly, these symptoms diminish after the initial weeks, highlighting the body’s capacity to adapt to the fasting routine.

However, specific populations, including children, pregnant and lactating women, underweight individuals, and those with specific medical conditions, should avoid ADF. Consultation with a healthcare provider is recommended before embarking on ADF, especially for those with existing medical conditions or taking medications.

What to Eat and Drink on Fasting Days

Complete Fasting Days: Hydration Essentials:

Staying adequately hydrated becomes paramount on complete fasting days, where you are restricted to zero caloric intake. Optimal choices include:

  • Water
  • Unsweetened coffee
  • Tea.

These beverages help quench thirst and contribute to a sense of fullness. Water, in particular, is instrumental in maintaining bodily functions and aiding in detoxification.

Modified Fasting Days: Strategic Caloric Intake:

For those opting for the modified approach of ADF, where you can take approximately 500 calories on fasting days, thoughtful food choices can enhance satiety and nutritional intake.

Focus on nutrient-dense, low-calorie options that provide a sense of fullness without compromising the principles of fasting. Consider incorporating high-protein foods, such as lean meats or eggs, and fiber-rich vegetables to promote feelings of satiety.

alternate-day fasting preparation

Modified Fasting Day Meal Ideas:

Experts suggest eating once, preferably at lunchtime, when doing modified ADF. Here’s a list of meal ideas you can follow if you’re new to fasting. These meal options offer about 500 calories.

  • Grilled Chicken Salad:
    • Grilled chicken breast (4 oz)
    • Mixed salad greens
    • Cherry tomatoes
    • Cucumber slices
    • Olive oil and vinegar dressing
  • Zucchini Noodles with Pesto and Shrimp:
    • Zucchini noodles (1 cup)
    • Grilled shrimp (4 oz)
    • Cherry tomatoes
    • Pesto sauce
  • Turkey and Avocado Lettuce Wraps:
    • Sliced turkey breast (3 oz)
    • Avocado slices
    • Lettuce leaves for wrapping
    • Mustard or mayonnaise
  • Cauliflower Fried Rice with Tofu:
    • Cauliflower rice (1 cup)
    • Tofu cubes (1/2 cup)
    • Mixed vegetables (bell peppers, peas, carrots)
    • Soy sauce
  • Salmon and Asparagus Bundles:
    • Baked or grilled salmon fillet (4 oz)
    • Asparagus spears
    • Lemon zest
    • Olive oil
  • Egg and Spinach Omelette:
    • Eggs (2)
    • Spinach leaves
    • Feta cheese
    • Cherry tomatoes
  • Greek Salad with Chicken:
    • Grilled chicken breast (4 oz)
    • Feta cheese
    • Kalamata olives
    • Cucumber and red onion
    • Greek dressing
  • Cabbage and Beef Stir-Fry:
    • Ground beef (4 oz)
    • Shredded cabbage
    • Bell peppers
    • Soy sauce
  • Avocado Tuna Salad:
    • Canned tuna in water (3 oz)
    • Avocado cubes
    • Celery and red onion
    • Lemon juice
  • Mushroom and Spinach Frittata:
    • Eggs (2)
    • Mushrooms and spinach
    • Parmesan cheese
    • Olive oil

My Experience

Alternate-day fasting is a straightforward intermittent fasting approach.

Complete ADF can be very effective but is harder to stick to than standard time-restricted eating, such as the 16/8 method.

Many people reward themselves with unhealthy food on eating days, ruining results.

Low-carb and keto foods are most effective for ADF since it also puts you into ketosis.

Frequently Asked Questions

How many hours should I fast for on alternate-day fasting?

The fasting period typically extends for 36 hours on complete alternate-day fasting, with some variations allowing for a modified approach with a limited calorie intake. For modified ADF, studies suggest taking 500 calories at lunchtime, when your body needs most of the calories, where you get about 18 hours of fasting.

What are the results of 30-day alternate-day fasting?

Results may vary among individuals and the type and timing of your ADF. However, studies show that adherence to a 30-day alternate-day fasting regimen often leads to significant weight loss, improvements in metabolic markers, and other associated health benefits.

What are the rules for alternate-day fasting?

The critical rule is abstaining from food during fasting hours and eating as you please after fasting. For complete ADF, you should for up to 36 hours while drinking as many calorie-free drinks as needed. For modified ADF, this includes eating one meal, preferably at lunchtime, and fasting for up to 18 hours before feasting.

References

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2Pascual, P. E., Rolands, M. R., Eldridge, A. L., Kassis, A., Mainardi, F., Lê, A., Karagounis, L. G., Gut, P., & Varady, K. A. (2023). A meta‐analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time‐restricted eating for weight loss. Obesity (Silver Spring, Md.), 31(Suppl 1), 9-21. https://doi.org/10.1002/oby.23568

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8Yuan, X., Wang, J., Yang, S., Gao, M., Cao, L., Li, X., Hong, D., Tian, S., & Sun, C. (2022). Effect of Intermittent Fasting Diet on Glucose and Lipid Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis. International Journal of Endocrinology, 2022. https://doi.org/10.1155/2022/6999907

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10Cai, H., Qin, L., Shi, Y., Chen, H., Zeng, J., Zhou, W., Chen, Q., & Chen, Y. (2019). Effects of alternate-day fasting on body weight and dyslipidaemia in patients with non-alcoholic fatty liver disease: A randomised controlled trial. BMC Gastroenterology, 19. https://doi.org/10.1186/s12876-019-1132-8

11Varady, K. A., Bhutani, S., Klempel, M. C., Kroeger, C. M., Trepanowski, J. F., Haus, J. M., Hoddy, K. K., & Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition journal, 12(1), 146. https://doi.org/10.1186/1475-2891-12-146

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13Varady, K. A., Bhutani, S., Klempel, M. C., & Lamarche, B. (2011). Improvements in LDL particle size and distribution by short-term alternate day modified fasting in obese adults. The British journal of nutrition, 105(4), 580–583. https://doi.org/10.1017/S0007114510003788

14Mulas, A., Cienfuegos, S., Ezpeleta, M., Lin, S., Pavlou, V., & Varady, K. A. (2023). Effect of intermittent fasting on circulating inflammatory markers in obesity: A review of human trials. Frontiers in Nutrition, 10. https://doi.org/10.3389/fnut.2023.1146924

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17Bruce-Keller, A. J., Umberger, G., McFall, R., & Mattson, M. P. (1999). Food restriction reduces brain damage and improves behavioral outcome following excitotoxic and metabolic insults. Annals of neurology, 45(1), 8–15.

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20Ezpeleta, M., Gabel, K., Cienfuegos, S., Kalam, F., Lin, S., Pavlou, V., & Varady, K. A. (2023). Alternate-Day Fasting Combined with Exercise: Effect on Sleep in Adults with Obesity and NAFLD. Nutrients, 15(6). https://doi.org/10.3390/nu15061398

21Hoddy, K. K., Kroeger, C. M., Trepanowski, J. F., Barnosky, A. R., Bhutani, S., & Varady, K. A. (2015). Safety of alternate day fasting and effect on disordered eating behaviors. Nutrition journal, 14, 44. https://doi.org/10.1186/s12937-015-0029-9

22Gao, J., Xu, C., Zhang, M., Liu, J., Wu, X., Cui, C., Wei, H., Peng, J., & Zheng, R. (2022). Functional fiber enhances the effect of every-other-day fasting on insulin sensitivity by regulating the gut microecosystem. The Journal of nutritional biochemistry, 110, 109122. https://doi.org/10.1016/j.jnutbio.2022.109122

23Stekovic, S., Hofer, S. J., Tripolt, N., Aon, M. A., Royer, P., Pein, L., Stadler, J. T., Pendl, T., Prietl, B., Url, J., Schroeder, S., Tadic, J., Eisenberg, T., Magnes, C., Stumpe, M., Zuegner, E., Bordag, N., Riedl, R., Schmidt, A., Kolesnik, E., … Madeo, F. (2019). Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell metabolism, 30(3), 462–476.e6. https://doi.org/10.1016/j.cmet.2019.07.016

24Barnosky, A., Kroeger, C. M., Trepanowski, J. F., Klempel, M. C., Bhutani, S., Hoddy, K. K., Gabel, K., Shapses, S. A., & Varady, K. A. (2017). Effect of alternate day fasting on markers of bone metabolism: An exploratory analysis of a 6-month randomized controlled trial. Nutrition and Healthy Aging, 4(3), 255-263. https://doi.org/10.3233/NHA-170031

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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