Intermittent Fasting

What is it?

A popular way of eating that cycles between periods of fasting, with either no food or significant calorie restriction, and periods of eating. The periods of eating are often unrestricted in terms of the types of foods that can be eaten. Rather than focusing on what you eat, this diet focuses on when you eat. There are several different ways it can be done.

• Alternate-day fasting: this is when someone alternates between days of eating, or no food restriction, with days where they eat one meal only that provides approximately 25% of their daily calories.

• Whole-day fasting: this is when someone will do 1-2 days per week of complete fasting, or only up to 25% of their daily calorie needs, while eating regularly on the other days.

• Time-restricted: this is when people will eat normally during the day, but have specific times where they will fast, for example meals are eaten between 8am and 5pm, and then they fast after 5pm.

What does it do?

Fans of this diet say that it may help to change body composition through the loss of both weight and fat, and improve other health markers like cholesterol and blood pressure.

What does the research say?

In November of 2022 a research paper was published in the Journal of the Academy of Nutrition and Dietetics which stated that people who skipped meals, fasted, or ate their meals too close together had a greater risk of dying prematurely. This study analyzed data from the NHANES and found that people who ate only one small meal a day were more likely to die prematurely than those who ate more small meals each day. People who skipped breakfast or ate their meals very close together were more likely to develop cardiovascular disease.

Animal studies have suggested that calorie restriction can not only increase lifespan but improve tolerance to different metabolic stressors. Although this evidence is strong, scientists have been unable to reproduce these results in human studies.

A systematic review of 40 studies found that intermittent fasting resulted in weight loss, approximately 7-11 pounds, over a 10-week period of time. The authors of this review concluded that the intermittent fasting studies actually had a high drop-out rate, and therefore were a bit more difficult to follow than other studies looking at weight loss diets. In addition, when reviewing 12 clinical trials that compared a fasting group with a group who continuously calorie restricted, there were no significant differences in weight loss or body composition.

A randomized controlled trial that observed 100 obese individuals over a 1-year period of time did not find intermittent fasting to be better at initiating weight loss than continuous calorie restriction. In addition, there were no significant differences in heart rate, blood pressure, fasting insulin, and fasting glucose between the groups. At 12 months there were no differences in triglycerides or total cholesterol, and the fasting-group actually showed increases in LDL cholesterol. The drop-out rate was higher in the fasting group than in the calorie restriction group and those in the fasting group ate less food than was prescribed on non-fasting days and ate more food than prescribed on fasting days.

A one-year randomized trial also did not find intermittent fasting to be more beneficial than continuous calorie restriction.

What are the downsides?

Intermittent fasting may be very difficult to maintain. It is inappropriate for someone with a diagnosed metabolic issue. An example would be diabetes which requires consistent eating (e.g., meals and snacks) to maintain blood sugar in an even state. Prolonged periods of fasting have been shown to increase episodes of overeating. Lastly, it may create unhealthy behaviors and attitudes towards food.

Please who should avoid eating this way:

• Those with diabetes and other metabolic disorders

• Those diagnosed with eating disorders

• Adolescents, or individuals in an active stage of growth

• Those who require food to take medications

• Those who are pregnant or breastfeeding.

Bottom line

There are still lots of unanswered questions about intermittent fasting and more quality research is needed to show whether it is in fact beneficial. Research to date has not supported it as a good diet to follow. As always, it is recommended to check with your medical doctor and dietitian before starting any diet that would require significant food or calorie restriction.

References

Harvard T. H. Chan School of Public Health. (n.d.). Diet Review: Intermittent Fasting for Weight Loss. Retrieved from https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/

Johns Hopkins Medicine. (n.d.). Intermittent Fasting: What is it, and how does it work? Retrieved from https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work