Dietitian, Chantal Walsh, explain the how intermittent fasting works and how it is an eating pattern rather than eating plan.
Intermittent fasting (IF) has become quite a buzzword and there is no shortage of freely available information about it. With its many promises to assist with weight loss, especially around the belly, control insulin levels and help brain function, it’s no wonder that we are all intrigued by this new pattern of eating.
What is intermittent fasting?
It’s an eating pattern that cycles between periods of fasting and feeding. During the fasting phase, there is a significant restriction of calories. On feeding days, there is no specific calorie requirements or certain types of foods recommended but rather focuses on when you should be eating them. It’s therefore not an eating plan but rather an eating pattern.
Patterns of intermittent fasting
There are numerous patterns of intermittent fasting that can be used.
In this pattern, you will fast for 16 hours and then eat for eight. This is often the pattern where we skip breakfast and only start eating about 16 hours after your last evening meal. This is followed for seven days a week.
With this pattern, you will restrict your calorie intake to 500 – 600 calories for two non-consecutive days, while the other five days you have your normal consumption.
Eat stop eat
This involves a 24-hour fast one to two times per week, where no calories are consumed on those days.
In this pattern, there is a restriction of calorie intake every second day (to around 500 calories), while on the feed days you continue your normal intake.
This fast focuses on a 20-hour fasting period followed by a 4-hour feasting period. This is normally for the dinner meal that is a large portion of unrestricted foods.
The last of the fasting patterns is where you choose a meal or two to skip as and when you feel it necessary.
What does science say? Firstly, let’s look at reduction in adipose tissue and weight loss. It’s suggested that due to the limited time that you get to ‘feed’ that there is a reduction in calories and therefore results in weight loss.
In a review1, it was found that intermittent fasting reduced body weight by 3–8% over a period of 3–24 weeks. This was on condition that the food items that were chosen during the ‘feeding’ times where healthy food choices. Ensuring that the meals were balanced, incorporating loads of vegetables, lean vegetables and complex carbohydrates.
It’s therefore important to consider the nutrient density of the food choices, ensuring an intake of a variety of vitamins, minerals and other essential elements.
An observational study2 of overweight and obese men during the religious fast of Ramadan reported that since obesity is accompanied by increases in adiposity and changes in appetite-regulating hormones, if we decrease weight it alters the abnormal release of these hormones, which might be useful in managing obesity. Ramadan IF improved body composition and produced some positive changes in these hormones, these changes in hormone levels persisted for three weeks after the end of Ramadan.
With the possible weight loss that is experienced with calorie conscious IF, glucose (sugar) and lipid (blood fat) can also be improved. A 2017 review3 on intermittent energy restriction (IER) and time-restricted feeding (TRF) found that there are possible benefits of these styles of eating on weight loss and metabolic health. However, most of the studies are on animals and there is very little evidence currently in human studies.
In comparison to a calorie-controlled, nutrient density diet, it was found that long-term the effects on weight loss and lifestyle health benefits are similar to that of IF.
Yay or nay?
If you are considering intermittent fasting, consider the type of IF programme that suits you and ensures that you don’t get too hungry or that it affects your mood stability. Ensure that the types of foods that you choose are nutrient dense and full of vitamins and minerals. Monitor the calorie intake; you still want to stay within your specific daily requirements. It will take time to adjust to the new style of eating and for the body to adjust, be patient.
It’s important to remember that IF is one of the tools in your nutrition toolbox, it will need to be combined with basic nutrition guidelines, sufficient water intake and exercise. To help with the success of this style pattern, please contact a registered dietitian.
- Barnosky et al., 2014
- Zouhal et al., 2020
- Antoni et al., in 2017