Intermittent fasting: Is it all it's cracked up to be?

Intermittent fasting is 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.

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

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 may be 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 behaviors, 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.


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.

Potential downsides

Despite the many touted benefits of intermittent fasting, there are also some downsides.

Side effects

Intermittent fasting may be safe for heart and metabolic health, but according to a 2017 review, it may induce negative side effects in some people, such as:

• increased feelings of hunger

• heightened irritability

• worsened mood

• increased thoughts about food

• fatigue

• fears of feeling out of control around food

• overeating during eating windows

• difficulty concentrating.

Quality of evidence

Additionally, most of the research on intermittent fasting is based on animal research, with little long-term human research available.

Furthermore, a 2021 review found that only six out of 104 alleged health benefits of intermittent fasting were supported by moderate- to high-quality evidence, and most findings were based on low-quality research. This means that more rigorous human research on the long-term health benefits of intermittent fasting is warranted.

Alternative non-fasting diets that produce similar results to intermittent fasting include calorie restriction and the Mediterranean diet. –


Science-backed benefits of fasting

1. Improved cholesterol levels

2. Blood sugar control

3. Changes in body composition

4. May lower inflammation, risk of breast cancer and other inflammatory conditions.

5. May significantly reduce the risk of heart disease.

Did you know?

Mediterranean diet

Research shows its protective nature against the development of colorectal cancer and the loss of nerve cells in Parkinson’s disease.

Health tip

Focus on fruits, vegetables, whole grains, lean proteins from fish and good fats.

Health precaution tip

Limit consumption of sweets and red meats.

Speak to a nutritionist to guide you in designing a diet plan that works for you.


Namibian Sun 2023-12-07

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