Intermittent fasting, also known as IF, refers to general concept of alternating periods of eating and fasting. During the fasting period, there is a significant reduction in calorie intake, whereas during the eating window (time when meals are consumed), food can be eaten without restrictions. Therefore, the main principle of the IF diet – intermittent calorie restriction – differs significantly from the traditional low-calorie diet, which involves continuous calorie limitation.

This raises important questions: Is IF an effective eating model for reducing body weight and fat mass? And which approach – intermittent fasting or the traditional low-calorie diet – would be a better choice for achieving these goals?

Types of IF diets

TRF – time-restricted feeding

Time-restricted feeding is an eating model that involves consuming meals within specific time windows. The most common patterns are 16/8, 18/6 and 20/4. First number refers to the duration of eating window, while the second indicates fasting period. In the 16/8 pattern, for example, a person eats during a 16-hour window and fasts for the remaining 8 hours. Real-life example of a TRF model is Ramadan, observed by practicing Muslims who fast strictly from sunrise to sunset.

ADF – alternate-day fasting

Alternate-day fasting is an eating model where 24-hour fasting periods alternate with 24-hour eating periods. Several variations exist, such as 6/1, 5/2 and 4/3. First number represents the number of days per week when food is consumed normally, and the second refers to fasting days. For instance, someone following the 5/2 pattern would eat normally for 5 days of the week and fast for the remaining 2 days.

Principles of intermittent fasting

Types of eating models (TRF and ADF) define the main structure of intermittent fasting approach. However, when it comes to food choices or calorie intake, IF does not impose any specific restrictions.

That being said, even if the primary goal of implementing intermittent fasting is weight loss (which requires achieving a calorie deficit), it is still important to follow the principles of healthy eating. This includes composing balanced meals that provide all macronutrients (proteins, fats and carbohydrates) and incorporating foods from all major food groups: vegetables and fruits, grains, dairy products, protein sources and healthy fats. Additionally, it is advisable to limit the intake of highly processed foods and avoid unnecessary snacking.

By maintaining healthy body weight, engaging in regular physical activity and following balanced diet, we can effectively support good health, maintain proper blood glucose levels and reduce risk of chronic diseases.

Intermittent fasting in light of scientific literature

In July 2019, results of randomized controlled trial were published, aiming to compare intermittent and continuous calorie restriction, with focus on their effects on insulin sensitivity and associated cardiometabolic mechanisms.

The study was conducted among individuals with abdominal obesity (43 participants), who were divided into two groups:

  1. intermittent calorie restriction: consuming 600 kcal per day for 2 days, followed by balanced diet for the remaining 5 days;
  2. continuous calorie restriction: following balanced diet with a consistent reduction of 500 kcal per day.

Intervention lasted 4 weeks for both groups. Afterward, selected markers of insulin sensitivity and cardiometabolic risk were assessed.

Study findings regarding the IF diet indicated that:

  • Weight loss was comparable between the two groups.
  • Insulin sensitivity (measured by the QUICKI index) improved in both groups, with no significant differences between them.
  • Fasting plasma glucose levels decreased after following traditional weight-loss diet but remained unchanged with intermittent fasting approach.
  • Fasting plasma free fatty acid levels were lower after intermittent fasting intervention compared to continuous calorie restriction.
  • Lipid levels, inflammation markers, ambulatory blood pressure monitoring (ABP) and heart rate variability (HRV) were comparable between the two groups.

Conclusions from the study:

  • Short-term use of either standard weight-loss diet or intermittent fasting produces very similar effects on the body.
  • If intermittent fasting suits your lifestyle and makes you feel good, it is absolutely a viable option to follow.
  • However, if you plan to adopt intermittent fasting solely because it is currently “trendy” and you expect it to accelerate your results, unfortunately — that won’t happen. Whether you choose a standard calorie-restricted diet or IF will not make a meaningful difference in such a case.

Summary

Research on effectiveness of intermittent fasting (IF) shows that its effects on weight loss and improvements in insulin sensitivity are comparable to those of traditional low-calorie diets. In one study, the outcomes of IF were compared with those of continuous calorie restriction in a group of individuals with abdominal obesity. Results demonstrated that both approaches were equally effective in reducing body weight and improving insulin sensitivity.

Moreover, IF may offer additional benefits, such as lower levels of plasma free fatty acids, which is advantageous for metabolic health. Nonetheless, it is important to remember that there is no one-size-fits-all approach to nutrition. Choice between IF and traditional calorie-reduction diet should be tailored to individual preferences, lifestyle and the body’s response.

In summary, IF can be just as effective as traditional weight-loss methods, but like any diet, it must be adapted to personal needs and circumstances. Before starting IF, it is important to consult with a dietitian or doctor, especially if you have any medical conditions or specific dietary requirements.

Sources:

  1. Kaźmierczak A., Perkowska K., Kiełb A., Borkowska A., Izdebska W., Stanek J., Sornek P., Pawlak I., Mich A., Ciesielski R., Effects of intermittent fasting on weight loss and metabolic health, Quality in Sport, 2024, Vol. 22, p. 54618
  2. Patterson R. E., Laughlin G. A., Sears D. D., LaCroix A. Z., Marinac C., Gallo L. C., Hartman S. J., Natarajan L., Senger C. M., Martinez M. E., Villasenor A., Intermittent fasting and human metabolic health, J Acad Nutr Diet., 2015, 115(8):1203–1212
  3. Pinto AM, Bordoli C, Buckner LP, Kim C, Kaplan PC, Del Arenal IM, Jeffcock EJ, Hall WL. Intermittent energy restriction is comparable to continuous energy restriction for cardiometabolic health in adults with central obesity: A randomized controlled trial; the Met-IER study. Clin Nutr. 2019 Jul 30. pii: S0261-5614(19)30296-1