Many religions practise fasting at certain times of the year as a spiritual and physical cleanse. But the question is, what is intermittent fasting and how does it work?
Have you ever eaten your breakfast late or only eaten twice a day? Then you were following an intermittent fasting pattern, without knowing it! Intermittent fasting is not a specific diet, it is just a rearranged time pattern of eating.
Just as humans have different eating patterns, so there are different intermittent fasting patterns. Most patterns will lead to energy restriction, because you are reducing the amounts of times you eat, keeping portion sizes of meals the same as before.
There are two fundamental variants of intermittent fasting, namely time-restricted feeding and alternate-day fasting.
Fundamental variants of intermittent fasting
With time-restricted feeding, there is a window of a few hours in the day where you are allowed to eat. The rest of the day you can only drink water.
There are three different patterns of time distribution. You can either fast for 16, 18 or 20 hours. The remaining hours will then be for your meals (i.e. 8, 6 or 4 hours). Most of the fasting period can be planned around night-time, close to bedtime, to avoid disrupting your circadian rhythms.
Physically active people following time-restricted feeding patterns reported weight reduction while maintaining muscle mass, which led to athletes achieving their desired body mass for a sporting event.
For alternate-day fasting, you fast a few days a week, and eat the other days in a 5:2 or 4:3 ratio, where you pick 2 or 3 days of the week to fast and the other 4 or 5 days you eat normally. You can either fast in the days consecutively or you can separate them during the week. During fasting days you may still consume about 25% of your normal energy needs (400 to 600 kcal). In contrast with religious fasting, people will not be allowed to consume anything on fasting days.
Alternate-day fasting is associated with reducing belly fat and fat around your internal organs as well as reducing LDL cholesterol. Intermittent fasting may reduce atherosclerosis (a risk factor in heart disease) and lower inflammation blood values (e.g. Interleukin-6, homocysteine, and C-reactive protein).
A beneficial effect was also seen in lowering blood pressure. Statistically significant improvements in blood sugar control were found in overweight or obese pre-menopausal women who were following a 5:2 eating pattern. Reduced insulin requirements without weight loss were found in men with pre-diabetes.
Beware of intermittent fasting under these circumstances
Intermittent fasting can be beneficial in certain circumstances, bearing in mind that you make healthy food choices and practise portion control and ensure that you drink enough fluids. There are some risks, however.
People may experience low blood sugar, malnutrition, vitamin and mineral deficiencies, dehydration, headaches and mood swings. It needs to be practised with caution under the supervision of a health-care professional (doctor and/or nutritionist), especially in people who suffer from a disease such as diabetes, hypertension, heart disease. It is not safe for pregnant as well as lactating women, young children, underweight people, frail older adults, people with immunodeficiencies, hormonal imbalances or eating disorders.
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