To achieve weight loss, a person needs to restrict his or her calorie intake by at least 20%. One method that has gained favour in recent years is known as intermittent fasting. This refers to abstaining from food and calorific drinks for certain periods of time, alternating with periods of normal eating and drinking in between. Intermittent fasting can also be combined with other eating plans such as low-carbohydrate diets. The average weight loss with intermittent fasting is 4-10% of body weight in 4-24 weeks.

Historically, humans have had periods of feeding followed by periods of no food intake, allowing the body’s metabolism to adapt to both situations, with storage of excess calories in the “fed state” and consumption of these stores in the “fasting state”. In recent years, humans have increasingly adopted a grazing routine with snacks between meals making the “fed-state” the predominant state for most of the day. This has resulted in increased insulin levels (figure 1), excess weight gain, and associated metabolic factors such as higher blood glucose and cholesterol levels, elevated blood pressure, and an increased risk of diabetes and cardiovascular disease.

Fasting promotes changes in metabolism, cellular processes and hormonal secretion, all of which result in greater insulin sensitivity and reductions in glucose levels, blood pressure, body fat, lipids, and inflammation. In humans, 12-24 hours of fasting significantly reduces glucose levels and liver glycogen, causing the body to switch to a ketogenic mode using fatty acids and fat-derived ketones as energy sources

How Intermittent Fasting Can Help You to Lose Weight by Dr Mohgah Elsheikh

The most popular option of intermittent fasting is time-restricted feeding (16:8), which involves eating during an 8-hour window (maximum) of each day, for example, between 12-8 pm (figures 2 and 3). For the remaining 16 hours, water is recommended and drinks with no calorific value may be consumed, for example, black/green tea, or black coffee. Evidence suggests that even after the fast, individuals do not compensate with a larger meal. Skipping breakfast ensures that the fat-burning fasting state lasts for most of the night, resulting in weight loss (figure 3).

In research, intermittent fasting in mice has been associated with improvements in health including diabetes remission and prevention, improved markers of cardiovascular disease and lipids and some suggestion of improvement in markers of cancer and prolongation of life. Studies in humans are ongoing, but so far, they show evidence of weight loss, improved blood pressure and cholesterol levels, increased insulin sensitivity and reduced glucose levels.

Intermittent fasting is safe and tolerable for most individuals, however, it might be harmful to specific populations such as children, pregnant women, the elderly and underweight individuals and therefore is not recommended in these cases.

Adverse effects of intermittent fasting are similar to those of a ketogenic diet; they include halitosis (bad breath), fatigue, weakness and headaches, particularly during the first few days of starting the diet. Adequate hydration helps to alleviate some of the symptoms.