Intermittent Fasting: The ideal diet for weight loss?


The Intermittent Fasting diet pattern has gained popularity recently. Fasting is known to be one of the oldest traditions in the world and has been used in various communities for either cultural or religious reasons, as well as a healing method for illnesses in the past. Hippocrates, the father of modern medicine, once wrote: "To eat when you are sick is to feed your disease."

The three most popular approaches to intermittent fasting are:

  • Alternate fasting: Alternating between days with no food restriction with days consisting of one meal that provides about 25% of daily calorie requirements. Example: Mon-Fri consists of fasting, while alternate days have no calorie restriction.
  • 5-2 fasting: Following a normal diet five days per week and fasting two days per week.
  • Time-restricted feeding (IF): Food intake only within an 8-hour window each day. For example, food intake starts 12 noon to 8 pm, followed by a 16-hour fast where only water, coffee and tea are allowed.

The benefits of intermittent fasting:

  • Immune response that repairs cells: when we don't eat for many hours, our cells start a cellular "waste removal" process, called autophagy.
  • Promoting positive metabolic changes (lower triglycerides, LDL cholesterol, blood pressure, fat mass, blood glucose).
  • Promoting Ketosis: a process that occurs when the body doesn't have enough glucose for energy, so it breaks down stored fat. This causes an increase in substances called ketones and, combined with fewer calories consumed overall, can lead to weight loss.
  • Reducing oxidative stress and inflammation, such as arthritis and asthma.
  • Improved blood sugar regulation and body stress response.
  • Changes in gut microbiota.
  • Effect on the biology of the circadian rhythm (the 'biological clock' day-night).
  • Improvement of insulin resistance, reducing the risk of type II diabetes.

Is intermittent fasting a reliable strategy for achieving weight loss?

A randomized controlled trial, where 100 obese people participated for a year, did not find that intermittent fasting was more effective than daily calorie restriction, the classic diet based on energy deficit. There were no significant differences in weight loss, weight regain or body composition (e.g. fat, lean mass).
Weight loss effects in intermittent fasting are mainly due to achieving a negative energy balance. Combining intermittent fasting with energy restriction could add additional weight loss (3% to 8% on average, based on current data) and bring about beneficial effects on cardiometabolic markers such as blood pressure, LDL cholesterol, triglycerides and blood sugar levels.

Possible side effects of intermittent fasting:

  • Increased hunger
  • Fatigue
  • Irritability
  • Decreased concentration
  • Nausea
  • Constipation
  • Headache
  • Loss of lean muscle mass: Given the importance of lean muscle mass in increasing metabolic rate, regulating blood sugar and maintaining overall physical fitness, it is recommended to combine resistance training with an intermittent fasting protocol.
Most side effects subside within a month.
It is worth paying attention to the fact that the various dietary patterns that occasionally gain popularity are not intended for everyone, as everyone is different, with completely different needs. The dietary pattern of intermittent fasting is therefore not suitable for:

  • People with eating disorders (anorexia, orthorexia or bulimia nervosa).
  • Active stages of development, such as in children and adolescents.
  • Pregnancy & breastfeeding.
  • Diabetes.
  • People suffering from gastritis, acid reflux and irritable bowel syndrome.
In conclusion

Intermittent fasting leads to similar weight loss as the classical hypocaloric diet. It is not better or superior. Although some benefits of caloric restriction have been demonstrated in animal studies, similar benefits of intermittent fasting in humans have not been observed. It is not clear, therefore, if intermittent fasting is superior to other weight loss methods in terms of weight loss, biological changes, compliance rates and reduced appetite.
Cases where intermittent fasting can be beneficial are in some people who usually eat one or two meals a day or do not eat for long periods of time. These individuals seem to show better compliance with this eating pattern. In addition, individuals who tend to overeat or snack in the evening may benefit from limited eating time, especially if late eating leads to unpleasant side effects such as reflux or sleep disturbance.

Scientific References

Correia JM, Santos I, Pezarat-Correia P, Minderico C, Mendonca GV (2020). Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis. Nutrients. May 12;12(5):1390.

Horne B.D., Muhlestein J.B., Anderson J.L.(2015) Health effects of intermittent fasting: Hormesis or harm? A systematic review. Am. J. Clin. Nutr. ;102:464–470.

Tinsley G.M., Forsse J.S., Butler N.K., Paoli A., Bane A.A., La Bounty P.M., Morgan G.B., Grandjean P.W. (2017) Time-restricted feeding in young men performing resistance training: A randomized controlled trial. Eur. J. Sport Sci. ;17:200–207.

Anton S.D., Moehl K., Donahoo W.T., Marosi K., Lee S.A., Mainous A.G., 3rd, Leeuwenburgh C., Mattson M.P.  (2018). Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring);26:254–268.

Katia Annousi

Dietitian & Nutritionist, QMU

Wellness Coach

Specialized in Eating Disorders & Metabolic Diseases