Here with you is your personal trainer Gregory Kandiba. I'm often asked about the benefits and effectiveness of intermittent fasting. This nutrition method has become a real trend in the fitness world, and many clients are interested in whether they should try 16/8, OMAD or other popular protocols. Over the years of my practice, I've seen both enthusiastic reviews from those who achieved quick results with this approach, and disappointment from those who encountered the "rebound effect" and metabolic slowdown. In this article, I decided to summarize current scientific data so you can make an informed decision about whether intermittent fasting is right for you and what its long-term consequences are.
What is intermittent fasting?
Intermittent fasting (intermittent fasting) is one of the most discussed nutrition approaches of recent years. Instead of traditional calorie control and food composition, this method focuses on time intervals for food intake. The most popular protocols include:
- 16/8 — 16 hours of fasting and an 8-hour window for food intake
- 5:2 — 5 days of normal eating and 2 days with sharp calorie restriction (about 500-600 kcal)
- OMAD (One Meal A Day) — eating once a day
Proponents of this method claim that it not only promotes weight loss, but also improves metabolic markers, enhances cognitive functions and even increases life expectancy. However, what does science say about this method in the long term?
Short-term effects: promising results
There is a significant body of research demonstrating positive effects of intermittent fasting in the short term.
A meta-analysis conducted by Harris and colleagues (2018) showed that intermittent fasting protocols indeed lead to weight loss during the first 3-6 months of application[1]. On average, participants lost from 3% to 8% of their initial body weight.
A study in the New England Journal of Medicine demonstrated that intermittent fasting can cause a whole range of positive metabolic changes[2]:
- Increased insulin sensitivity
- Reduced inflammatory marker levels
- Improved blood lipid profile
- Activation of autophagy processes (cellular self-cleaning)
A recent study published in Cell Metabolism showed that even with the same amount of consumed calories, the intermittent fasting group demonstrated higher fat mass loss and better glycemic control indicators over 8 weeks[3].
Long-term perspective: physiological adaptation and metabolic consequences
Despite encouraging short-term results, new studies raise serious concerns about long-term consequences of intermittent fasting.
Adaptive thermogenesis and metabolic slowdown
Our body is evolutionarily programmed to protect against hunger. With prolonged calorie restriction, regardless of method (including intermittent fasting), the body initiates several protective mechanisms.
A study by Müller and colleagues (2016) in the American Journal of Clinical Nutrition showed that prolonged periods of calorie restriction lead to significant reduction in resting energy expenditure—a phenomenon known as adaptive thermogenesis[4].
In a landmark study of "The Biggest Loser" TV show participants, published by Fothergill and colleagues (2016), it was found that even 6 years after completing the weight loss program, participants' basal metabolism remained approximately 500 kcal below expected for their weight[5]. Although this study concerned general calorie restriction rather than strictly intermittent fasting, it demonstrates the critical concept of long-term metabolic adaptation.
Hormonal dysregulation
Trepanowski and colleagues (2017) in a study published in JAMA Internal Medicine found that while intermittent fasting may lead to initial weight loss, after one year the level of weight loss was comparable to traditional calorie restriction[6]. Additionally, a more pronounced decrease in leptin levels was observed—a hormone that regulates satiety and energy metabolism.
A study by Stekovic and colleagues (2019) revealed that prolonged intermittent fasting can lead to changes in thyroid hormone levels, which additionally contributes to metabolic slowdown[7].
Muscle mass loss
One of the insufficiently discussed consequences of intermittent fasting is potential muscle mass loss. A study by Tinsley and colleagues (2017) showed that without adequate protein intake during eating periods, intermittent fasting can lead to significant loss of lean body mass[8].
Since muscle tissue is more metabolically active than fat tissue, its loss additionally contributes to metabolic slowdown, creating a vicious cycle.
The phenomenon of "weight regain" and metabolic adaptation
Particularly alarming is the phenomenon of "weight regain" after a period of restrictive eating. A study by Hall and Kahan (2018) in Nature Reviews Endocrinology demonstrated that after significant weight loss, the body activates multiple compensatory mechanisms aimed at restoring initial body weight[9].
These mechanisms include:
1. Reduced energy expenditure — the body becomes more "economical" in energy spending
2. Changes in hunger and satiety hormone levels — increased ghrelin (hunger hormone) and decreased leptin and peptide YY (satiety hormones)
3. Changes in nutrient absorption efficiency — the body begins extracting more energy from the same food
A notable study by Weiss and colleagues (2020) showed that after intermittent fasting, when returning to normal eating regimen, participants gained weight faster and in greater volume compared to the control group[10]. This is explained precisely by long-term metabolic adaptation and the "rebound effect."
Individual variability and psychological aspects
It's important to note that reaction to intermittent fasting varies greatly between people. A study by Gonzalez and colleagues (2018) showed that genetic factors, initial metabolic status and even gut microbiome can influence the effectiveness and safety of this approach[11].
Psychological aspects also play a significant role. A study by Headland and colleagues (2016) showed that intermittent fasting can increase the risk of developing eating disorders and lead to unhealthy relationships with food[12].
Alternative approaches for long-term weight management
Given the above scientific data, more balanced approaches for long-term weight management can be suggested:
1. Moderate calorie deficit (10-20%) — A study by Leibel and Hirsch (1995) showed that a small but sustainable calorie deficit causes less metabolic adaptation compared to aggressive approaches[13]
2. Adequate protein intake (1.6-2.2 g/kg body weight) — A meta-analysis by Stokes and colleagues (2018) demonstrated that a high-protein diet promotes muscle mass preservation during weight loss[14]
3. Regular physical activity with emphasis on strength training — According to a study by Hunter and colleagues (2015), strength training partially prevents metabolic decline during calorie restriction[15]
4. Calorie cycling — Periodic increase in caloric intake (for example, 1-2 days per week) can help prevent metabolic adaptation, according to a study by Davoodi and colleagues (2018)[16]
Conclusion
Intermittent fasting undoubtedly represents an effective tool for short-term weight loss and certain metabolic improvements. However, scientific data indicate risks of long-term metabolic slowdown, hormonal dysregulation and weight regain when using this method over extended periods.
Instead of applying radical approaches, a more reasonable strategy appears to be creating a moderate calorie deficit through balanced nutrition, regular physical activity and forming sustainable eating habits that can be maintained throughout life.
As always, any weight management strategy should be individualized taking into account genetic, physiological and psychological characteristics of the person.
Personal guidance
If you're looking for an individual approach to nutrition and training that takes into account your metabolism peculiarities, lifestyle and goals, I offer personal trainer guidance. Within this program, we'll develop an optimal nutrition regimen considering the latest scientific data, create a training plan, and I'll personally monitor your progress with weekly strategy adjustments. My approach is based not on fashionable trends, but on scientifically based methods that ensure sustainable results without harm to metabolism. To book your first consultation and get additional information about the personal guidance program, write to private messages or fill out the form on my website.
Gregory Kandiba, Your guide to a better version of yourself
References
1. Harris L, et al. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports, 2018.
2. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine, 2019.
3. Sutton EF, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 2018.
4. Müller MJ, et al. Metabolic adaptation to caloric restriction and subsequent refeeding: the Minnesota Starvation Experiment revisited. American Journal of Clinical Nutrition, 2016.
5. Fothergill E, et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity, 2016.
6. Trepanowski JF, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, 2017.
7. Stekovic S, et al. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metabolism, 2019.
8. Tinsley GM, et al. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European Journal of Sport Science, 2017.
9. Hall KD, Kahan S. Maintenance of Lost Weight and Long-Term Management of Obesity. Medical Clinics of North America, 2018.
10. Weiss EP, et al. Compensatory changes in energy balance during dosed caloric restriction. American Journal of Physiology-Endocrinology and Metabolism, 2020.
11. Gonzalez JT, et al. Personalized Nutrition: Pretreatment Glucose Metabolism Determines Individual Long-Term Weight Loss Responsiveness in Individuals with Obesity on Low-Carbohydrate Versus Low-Fat Diet. International Journal of Obesity, 2018.
12. Headland M, et al. Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients, 2016.
13. Leibel RL, Hirsch J. Diminished energy requirements in reduced-obese patients. Metabolism, 1995.
14. Stokes T, et al. Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients, 2018.
15. Hunter GR, et al. Combined aerobic and strength training and energy expenditure in older women. Medicine and Science in Sports and Exercise, 2015.
16. Davoodi SH, et al. Calorie shifting diet versus calorie restriction diet: A comparative clinical trial study. International Journal of Preventive Medicine, 2018.
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