Intermittent fasting is an eating plan that switches between fasting and eating on a regular schedule. Research shows that intermittent fasting is a way to manage your weight and prevent — or even reverse — some forms of disease.
Intermittent fasting is becoming an increasingly popular weight loss dieting strategy. Beyond weight loss, however, the diet has promising benefits that may reduce the risk of developing some chronic, lifestyle diseases. In this Honest Nutrition feature, we explain all that you need to know about intermittent fasting, and whether it is worth the hype.
Intermittent fasting is a term used to describe a variety of eating patterns that have alternating periods of fasting — abstinence from foods — and eating. The fasting period may last from 12 hours per day to several consecutive days, with a consistent, recurring pattern over the course of a week. The main types of intermittent fasting are: modified fasting or the 5:2 diet — this protocol involves fasting for 2 non-consecutive days of the week, and eating normally for 5 days alternate-day fasting — fasting days are alternated with days where foods and beverages are consumed normally, without restrictions or time-restricted eating — a type of intermittent fasting that limits the “eating window” to 4–12 hours, inducing a daily fasting period of 12–20 hours.
Persons eat to satiety during their eating windows without caloric restrictions. Of these, time-restricted eating is the most popular, and maybe what most people refer to when they mention intermittent fasting. The 16:8 pattern — eating during an 8-hour window and fasting for 16 hours each day — may be the most recommended time-restricted eating pattern.
The circadian rhythm
Much of the research on intermittent fasting and time-restricted eating considers the impact of fasting on the body’s natural circadian rhythm.
The circadian rhythm, also called the circadian clock, represents the 24-hour cycle of metabolism in the body, including control of the sleep-wake cycle, blood pressure, mood regulation, and hormonal balance, to name a few. It is influenced by light and darkness over the course of the day, eating behaviours, and the timing of meals.
A growing body of research suggests that eating for lengthy periods in the day, ranging from 12–15 hours, may disrupt the circadian rhythm and increase the risk of chronic diseases including heart disease, cancer, and type 2 diabetes.
Thus, a major goal of fasting, specifically time-restricted eating is to reduce the time spent eating in the day by extending the overnight fasting period. The study of the relationship between circadian rhythms and food timing is called chrono-nutrition.
Benefits
Many of the benefits of intermittent fasting are attributed to daily fasting periods of no less than 12 hours, although some research suggests that a minimum of 16 hours of fasting may be required.
Generally, during 12–36 hours of uninterrupted fasting, the liver glycogen stores become depleted, overall metabolic processes are altered, and positive health effects are observed.
Here are some of the science-backed benefits of intermittent fasting.
Improved cholesterol levels
Findings across animal and human research show favourable changes in cholesterol levels. Intermittent fasting has the potential to reduce total cholesterol, triglycerides, LDL cholesterol or “bad” cholesterol, and increase HDL cholesterol or “good” cholesterol.
Elevated total cholesterol, LDL cholesterol, and triglyceride levels are risk factors for heart disease.
Blood sugar control
Intermittent fasting can improve blood sugar control by reducing insulin resistance, and increasing insulin sensitivity. This results in lower fasting blood sugar and glycated haemoglobin — HbA1c — levels.
In fact, experimental research in adult males with type 2 diabetes showed the potential for intermittent fasting as a therapeutic approach that may reduce the need for insulin therapy.
Changes in body composition
Changes in body weight and composition are among the most studied effects of intermittent fasting. Several studies have shown that weight loss of between 3–7% body weight in an average of 8 weeks was achievable through intermittent fasting.
Research also noted that this method could result in fat loss. Fasting in a 14:10 pattern — an eating window of 10 hours and a daily fast of 14 hours — can act on the risk factors of metabolic syndrome, including by reducing waist circumference, body fat percentage, and visceral fat.
