What is Intermittent Fasting (IMF)?
IMF focuses on when you eat rather than what you eat, switching between periods of fasting where caloric intake is little to none (except black tea, black coffee, water and sometimes diet drinks) and eating periods with no restrictions.
While fasting has been embedded in culture and religion for years , it has recently been gaining traction in the media, due to claims of improved metabolic health and weight management.
What are the types?
There are several approaches, all aiming to extend the time that the body goes without food.
5:2 Fasting
Continue normal dietary habits for 5 days of the week and fast for the remaining 2 days, limiting caloric intake to 500-800kcals. The position of fasting days depends on your preference, but it is advisable to separate them with at least one non-fasting day to avoid negative symptoms.
Alternate Day Fasting
Fast on every other day, limiting caloric intake to 500-800kcals. On non-fasting days you can resume your normal energy intake.
Time Restricted Eating (TRE)
Limit energy intake to a specified daily ‘eating window’. The most common is the 16:8 diet, consuming your usual diet in an 8 hour window and fasting for the remaining 16 hours of the day. Ideally the eating window would remain consistent (eg. 10am-6pm or 12pm-8pm every day). Other protocols have eating windows from 4 to 10 hours.
TRE is popular as it is thought to be easier to follow than full fasting days. This is thought to align our feed/fast cycles with our internal body clocks (circadian rhythms) to improve metabolic health. When these are out of sync (large evening meals/irregular eating patterns) there may be an increased risk of metabolic disturbance, including insulin resistance, glucose intolerance and weight gain.
In our next blog post, we will explore the potential benefits of IMF including weight loss, cardiovascular health and a special spotlight on the role of TRE in Type 2 Diabetes and considerations around the safety of IMF for certain groups of the population.