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Intermittent fasting

What is Intermittent Fasting? Intermittent fasting covers a range of different eating patterns where eating is restricted some of the time. Eating might be time-restricted every day, or instead there may be caloric restriction some days. For example, a time-restricted feeding pattern may restrict eating to within a window of 8 hours a day. This would be known as ‘16/8’ where you fast for 16 hours and eat only during the other 8 hours of the day, every day.

What is Intermittent Fasting?

Intermittent fasting covers a range of different eating patterns where eating is restricted some of the time. Eating might be time-restricted every day, or instead there may be caloric restriction some days. For example, a time-restricted feeding pattern may restrict eating to within a window of 8 hours a day. This would be known as ‘16/8’ where you fast for 16 hours and eat only during the other 8 hours of the day, every day.

Image of clock on plate with knife and fork

Calorie Restriction

Intermittent fasting involving caloric restriction some days, is when an individual strictly limits calorie intake to below approximately 3360 kj (800 kcal) per day on some but not all days of the week. On the non-fasting days there is typically no caloric or dietary restriction in place. The most common intermittent fasting regime is the 5:2 diet, with 2 days of fasting (non-consecutive) and 5 days of eating at will.

image of calendar week. Monday: no caloric restriction, Tuesday: no caloric restriction, Wednesday: <3360 kj (800 kcal), Thursday: No caloric restriction, Friday: No caloric restriction, Saturday: <3360 kj (800 kcal), Sunday: No caloric restriction

The common 5:2 diet – no caloric restriction on 5 out of 7 days, and caloric restriction <3600 kj on 2 out of 7 days.

Since the caloric restriction is limited to only some days of the week it is often useful for those whose lifestyles make continuous caloric restriction difficult such as those who frequently eat out with work and struggle to commit to diets which require consistent lifestyle change every day of the week.

When recommending or supporting an individual in undertaking an intermittent fasting diet, attention and additional GP supervision should be recommended for those with chronic diseases such as insulin-dependent diabetes. Caution is also advised around possible fatigue and temporary disorientation during the fasting periods in individuals who are driving or working with heavy machinery.

Calorie Restriction – the Evidence

Calorie restriction has been shown in animals to increase lifespan as well as improve tolerances to various metabolic stresses in the body,24 however the evidence is less convincing in human studies. There is evidence to demonstrate that fasting yields an immune response that repairs cells and produces positive metabolic changes including a reduction in: triglycerides, LDL cholesterol, blood pressure, blood glucose and fat mass.25, 26 A common criticism of intermittent fasting diets is that dieters will over-eat during their non-fasting times to compensate for their lack of eating during fasting and hence will not result in calorie restriction overall. However, this has not been shown to be true when compared with other weight loss methods.25 A systematic review of 40 studies also found that intermittent fasting was effective for weight loss with a typical loss of 3-5 kg over 10 weeks.27

Intermittent Fasting Resouces

Click on the link to find out more evidence-based information around intermittent fasting https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/

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EduWeight: Weight Management for Adult Patients with Chronic Disease

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