The Ins and Outs of Intermittent Fasting

By now, the term “intermittent fasting” has become commonplace in many health and fitness circles. But it is still a relatively new term for most everyday folk. What does it mean? What health benefits or risks come along with it? Is it something that you should try? These are all questions that deserve answers.



What is Intermittent Fasting?
Intermittent Fasting (IF) is a term used to describe eating habits where an individual will completely restrict food intake during specific hours and only allow food intake during other allotted times. Common examples would be restricting food daily during a full 16-hour time period (sleep included), or every alternate day, or for two non-consecutive days during the week.

Optimal frequency, schedule and duration have not been identified so it is common to see various intermittent fasting protocols from different sources. Some people find it easy to only eat between 12pm-8pm everyday; while others prefer to have one or two days per week where they do not eat at all, allowing them to eat freely during the other days.

What Is Intermittent Fasting Supposed to Do?
Various methods of fasting and caloric restriction have been noted throughout history and in many cultural and religious circles. For example, Ramadan is a month of fasting during daylight hours that is observed by the Muslim community. Many health benefits have been anecdotally associated with these forms of fasting and it has led to this relatively new lifestyle approach of intermittent fasting.

Intermittent fasting typically, but not necessarily, leads to some caloric restriction which is a benefit for the majority of the population. It also has powerful metabolic effects with beneficial results on sugar and fat metabolism ultimately allowing for cellular repair and reduced risk of fat deposition. Positive effects on cognition have also been proposed.

What Does the Research Say about Intermittent Fasting?
While the vast majority of research on IF has been done in animal models, there are also preliminary human studies. Here are some of their highlights:

Clinical Studies: Varady et al. examined a 12-week period of alternate day fasting in 32 non-obese individuals and found an average loss of 6.5% body weight in the intervention group when compared to the non-fasting control group. Improvements in triglycerides, LDL cholesterol and C-reactive protein (a marker for inflammation) were also found in the fasting group.

One study done in 2013 found that overall mood (including tension, anger and confusion) was improved in 32 subjects over 12 weeks using a 2-day per week fasting regimen with concurrent caloric restriction. Improved blood pressure, total cholesterol, LDL cholesterol, weight and fat mass were all improved as well. However, due to a study design flaw, none of these findings could be deemed statistically significant so it is hard to say whether these benefits were real.

A separate 2013 study, known as the “FEELGOOD” trial, analyzed only one 24-hr period of fasting and one 24-hr period where the subjects were allowed to eat as they please. Findings during the fasting period showed marked but temporary increases in human growth hormone, red blood cell counts, hemoglobin and total cholesterol.

Observational Studies: Two observational studies have examined major adverse outcomes associated with fasting in humans. One observational study of 445 individuals found that those who reported routine fasting (typically of only one 24-hr fast per month) had lower odds of coronary artery disease than those who did not fast. A 2012 observational study examined 200 patients and confirmed the reduced risk of coronary artery disease and also found a significantly lower risk for diabetes in those who routinely fasted.


Application and Conclusions about Intermittent Fasting
Intermittent Fasting techniques are becoming more popularized for optimizing various markers of health, especially weight management. However, before this trend can gain merit, better designed and more rigorously studied trials must be performed to adequately assess the associated benefits and risks with IF. The current quality of evidence is still very preliminary.

Having said this, promising features of IF have been presented in the literature and in anecdotal practice. Consider these two additional benefits:

  1. Intermittent fasting may represent a high-compliance dieting technique that is relatively easy to implement for the general public. For example, many diets and nutritional guidelines require a certain level of knowledge in order to successfully employ (such as an understanding of ingredient names, macronutrient types and ratios, cooking techniques, etc). IF utilizes one simple rule surrounding a timing pattern that the general population should have no issue executing (i.e. no caloric intake during certain hours of the day or certain days of the week).
  2. IF has no direct financial costs in order to properly implement and, in fact, may allow for individuals to actually save on food expenses. From a public healthcare perspective, IF fits well within the overall focus of lowering healthcare costs on an individual level.

If you are considering trying an intermittent fasting routine, be sure to speak with a clinician that is well-versed on the topic in order to rule out any reasons why it may not be appropriate for your personal health circumstances. Regular monitoring and lab work should be done for signs of excessive weight loss, anemia, fatigue, malnutrition, and anorexia eating behaviour or binge eating behavior.


Select References:

Anson RM et al. Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Proc Natl Acad Sci USA 2003; 100:6216–20

Halagappa VKM et al. Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer’s disease. Neurobiol Dis 2007;26:212–20.

Martin B et al. Sex-dependent metabolic, neuroendocrine, and cognitive responses to dietary energy restriction and excess. Endocrinology 2007;148:4318–33.

Varady KA, et al. Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutr J 2013;12:146

Klempel MC et al. Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutr J 2010;9:35.

Horne BD et al. Health effects of intermittent fasting: hormesis or harm? A Systematic review. Am J Clin Nutr 2015;102:464–70.