Intermittent fasting: advantages and controversies

The concept of intermittent fasting (IF) gains more and more popularity among people who are interested in achieving fitness shape. The frequent argument used in case of supporting the efficiency of such kinds of methods are weak advantages connected with consuming meals every 2-3 hours. However, there have appeared many interesting studies describing the direct influence of short-term starvation and the IF methods on the parameters connected with shaping the body and improving health.

The author of the article:

Łukasz Kowalski is a doctoral student in the Department of Dietetics at the Faculty of Human Nutrition and Consumer Services at the Warsaw University of Life Science. He has individual concultations and dietetic seminars. He is also an author of several dozens of articles concerning nutrition and physical activity published in magazines such as: Kulturystyka i Fitness Sport dla Wszystkich, Fitness Authority and Muscular Development.


Modified alternate-day fasting (ADMF) is an IF method used most often in scientific studies with the use of patients with obesity and overweight. In case of ADMF, “the starving days” when the food intake is limited to 25% of the daily energy demand (it's usually one meal including 25% of the daily energy intake, eaten between 12-2p.m.), are alternate to the days of unlimited consumption.

Before some intensive research concerning the ADMF method were started, there were attempts of assessing the efficiency of other methods of IF, like alternate-day fasting (ADF), on small groups of volunteers in short period of time. The results of the preliminary studies were ambiguous. For example, Halberg et. al (2005), in his experiment done on eight men with obesity, observed the improvement of insulin sensitivity and the increase of the level of adiponectin after 2 weeks of using the IF method based on extending the night fasting to 20 hours [1]. By the way, adiponectin is a protein, which is produced by fatty tissue. Its level is decreased in case of insulin resistance and type 2 diabetes.

In other study done on 8 slim men, Soeters (2009), did not confirm the positive influence of the same IF method on insulin sensitivity, additionally, the volunteers noticed slightly higher decrease of the resting metabolic rate (RMR) using the IF methods, than in case of using standard diet [2]. The opponents of the IF methods often refer to these studies without taking under consideration their limitations (length: 2-3 weeks; number of volunteers: only 8-16 people).

Fortunately, there have been few more valuable studies done within the last few years (length: 8-12 weeks), which explain the advantages of using short-term starvation, especially the ADMF method [3]. In these experiments, the volunteers noticed many positive results, including:

  • decrease of body mass (-6-8% of the starting mass),

  • decrease of waistline,

  • decrease of the level of cholesterol – LDL fraction (-10-25%),

  • decrease of the level of triglycerides (-30-40%),

  • increase of the size of LDL molecules.

In one of the studies, the changes in the lipid profile were correlated with the positive changes of density of the mentioned adiponectin [4]. It's also interesting, that, on the basis of the current studies, the IF methods foster decreasing the lean body mass in lower degree than methods based on everyday calorific restrictions [5]. For example, Klempel (2013), in their study on 32 women (age: 25-65, BMI: 30-39.9 kg/m2) did not observe the loss of lean body mass after 8 weeks of using ADMF, independently from the version the women used – high-fat (ADF-HF; 45% of energy supplied from fat) or low-fat (ADF-LF; 25% of energy supplied from fat) [6]. Whereas, the loss of body mass in both versions was appropriately: 4.8% and 4.2% of the starting mass. Additionally, it was observed in many attempts done by Dr Krista Varady, that after about 2 weeks of following ADMF, there is the adjustment to the dietetic regime by the volunteers and the feeling of hunger on the starvation days is not that strong [7]. At the same time, on the days of unlimited consumption, the people supplied only about 100-110% of their energetic demand, which makes them use a diet with massive energetic deficit.

Can the IF methods be used in case of digestive tract problems?

In the context of using the IF methods, there aren't many who mention phase 3 of the migrating motor complex (MMC), i.e. the regular pressure waves syndrome, which is supposed to remove the remains of food from the area of small intestine during night and between the meals, as well as prevent from moving the bacteria from large intestine to small intestine. The lower activity of phase 3 of MMC was observed, among others, among the patients with the irritating bowel syndrome (IBS), which was connected with the occurrence of small intestine bacterial overgrowth (SIBO) [8]. It's also interesting, that one of the main researchers of the issues connected with IBS and SIBO – Dr Mark Pimentel, in his book “A new IBS solution”, suggests the patients with IBS to eat only 3 meals a day in order to increase the activity of the mentioned pressure wave, which prevents from developing SIBO. In that case, can the IF methods be used in minimizing the symptoms typical for IBS? Perhaps there will be some research supporting this thesis soon. So far, the possibility of using the IF methods is studied in dieto-therapy of overweight and obesity. However, at the end of this part, I would like to warn the enthusiasts of more hardcore methods of the IF – shortening the eating window to 2-4 hours and the feasst, like “Michael Phelps Diet Challenge” will not necessarily be good for the digestive tract.

Is training on empty stomach a bad idea?

In one of my previous articles, I mentioned the elite Ethiopian long-distance runners, who did more intensive training on empty stomach. In the same article I referred to the results of studies, which incline that doing the endurance workouts on empty stomach, after the night fasting, may improve the ability of fat oxidation during the physical effort and decrease the frequency of occurrence the fall of blood sugar caused by exercising [9]. Whereas, Deldicque (2010) observed, that resigning from a meal before the workout may be connected with an interesting compensation mechanism, as a result of which, the anabolic response to the after-workout meals is bigger [10]. In another article, I tried to underline the fact, that famous sports people (such as the best basketball player in the NBA history – Hakeem “The Dream” Olajuwon) are able to sustain great shape also during the Ramadan. There are more reasons to think that training on empty stomach is not such a bad idea. But is it the best solution in each case? For sure, it's not.

Does short-term starvation cause stress?

It sometimes happens that, in order to defend the IF methods, the studies in which one-time short-term starvation (less than 3-4 days) was introduced and it did not cause lowering the activity of thyroid and increasing excretion of cortisol [11]. However, it's good to have in mind the fact, that in case of the IF methods, the periods of time with starvation are repeated cyclically, and are not introduced only once. Whereas, the periods of consumption don't have to “reset” the signals connected with repeated periods of starvation. Concerning that, some part of the experts does not recommend this kind of methods (especially the more hardcore ones with the short eating window) in case of people who train at the edge of overtraining, who have very stressful lifestyle and problems with assuring proper supply of nutrients, as well as appropriate amount of quantity and quality of sleep. This suggestion seems reasonable.

Intermittent fasting and longevity

Many studies incline that calorific restrictions (~20-40% of the normal intake) may contribute to prolonging the life span (in case of laboratory animals), as well as to the improvement of many factors of risk of cardiovascular diseases, diabetes and neurodegenerative diseases. Temporary starvation is definitely an efficient way for calorific restriction [12]. Prolonging the length of life in case of calorific restrictions and the IF methods may be strongly connected with stronger phenomenon of autophagy, i.e. the mechanisms, in which a cell degrades the dead, damaged or used parts of its structure. By the way, it's good to have in mind the fact, that the studies connected with the influence of calorific restrictions on longevity are done on laboratory animals and are somehow limited. A convincing argument in the discussion seem to be the pictures of monkeys ( In this case, it's 'old' and ill Matthias, who was given a standard diet used in the studies on animals for 28 years on the left, and Rudy – on the right, in much better condition, despite being slightly older, who received a diet with calorific restrictions [13]. However, in both cases, despite the difference in the amount of calories, the diet was following (mass in %):

  • corn starch 30,

  • saccharose 28.5,

  • lactalbumin 15,

  • corn oil 10,

  • mix of mineral compounds 5.5,

  • dextrine 5,

  • celulose 5,

  • mix of vitamins 1.

Well, the diet of rhesus monkeys in reality looks a bit differently. That's why there are more frequent suggestions, that the positive result of calorific restrictions observed in the studies on animals may be largely connected with the consumption of adverse nutrients, which are included in a standard laboratory diet. There is no soubt about one conclusion we can draw from these studies – that the less junk food, the better.


In case of the IF methods, many issues require further research. However, the experiments, which have been done so far are promising and indicate that such kinds of methods may be an interesting alternative to the everyday calorific restrictions, when the aim is to lower the level of body fat.

Sources: 1) Halberg i wsp. (2005). Effect of intermittent fasting and refeeding on insulin action in healthy men. J Appl Physiol. 99: 2128-36. 2) Soeters i wsp. (2009). Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. Am J Clin Nutr. 90: 1244-51. 3) Varady i wsp. (2009). Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr. 90: 1138-1143. 4) Kroeger i wsp. (2012). Improvement in coronary heart disease risk factors during an intermittent fasting/calorie restriction regimen: Relationship to adipokine modulations. Nutr Metab (Lond). 2012. 9: 98. 5) Varady (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obes Rev. 12: e593-601. 6) Klempel i wsp. (2013). Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism. 62: 137-43. 7) Klempel i wsp. (2010). Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutr J. 3;9:35. 8) Pimentel i wsp. (2002). Lower frequency of MMC is found in IBS subjects with abnormal lactulose breath test, suggesting bacterial overgrowth. Dig Dis Sci. 47: 2639-43. 9) Van Proeyen i wsp. (2011). Beneficial metabolic adaptations due to endurance exercise training in the fasted state. J Appl Physiol. 110: 236-45.10) Deldicque i wsp. (2010). Increased p70s6k phosphorylation during intake of a protein-carbohydrate drink following resistance exercise in the fasted state. Eur J Appl Physiol. 108: 791-800.11) Zauner i wsp. (2000). Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Am J Clin Nutr. 71: 1511-5. 12) Varady i Hellerstein (2007). Alternate-day fasting and chronic disease prevention: a review of human and animal trials. Am J Clin Nutr. 86: 7-13. 13) Colman i wsp. (2009). Caloric restriction delays disease onset and mortality in rhesus monkeys. Science. 325: 201-4.