What is Intermittent Fasting?
Intermittent fasting has boomed in popularity in recent years and claims a huge array of health benefits. Intermittent fasting is a form of energy restriction where cycles of fasting and ‘eating windows’ are undertaken for different time-lengths. Most of us already fast between 8 -12 hours a day while asleep. However, intermittent fasting diets require longer fasting times than this.
Many athletes or those who are involved in a large variety of sports or gym explore intermittent fasting. Accredited Sports Dietitians are a fantastic source of support for this group to assist with a personalised approach according to the sport, individual and ensuring energy and nutrient requirements are met.
Aside from the sporting world, you may have heard people who intermittent fast when they are trying to lose weight. In today’s blog, we explore the good and the bad of intermittent fasting, the different techniques and if it is safe for those with IBS.
Main Ways to Intermittent Fast
16/8 Intermittent Fast
One of the most popular fasting techniques – this involves eating for a period of 8 hours during the day and fasting for 16 hours overnight. Most people will usually have their last meal at around 8pm, skip breakfast and have their first meal at noon.
5:2 Intermittent Fast
A more intensive form of fasting – where the week is split into 5 days of regular meal consumption and 2 days of fasting. On fasting days, energy intake is heavily reduced to 500-600 calories per day (~2000 to 2500 kJ). Variations of the 5:2 are 6:1, 4:3 or alternate day fasting.
Eat-Stop-Eat Intermittent Fast
Very similar fasting technique to the 5:2 – with 2 days of the week designated to fasting. These 2 fasting days are not consecutive and vary in length of time (usually between 16-24 hours). Unlike the 5:2, no food is consumed during fasting hours. Regular meals are eaten for the remaining 5-6 days.
There are so many ways to intermittent fast. There is even this intense method of intermittent fasting 7 days a week, Monday to Sunday from 10pm until 5pm the next day. So, for 5 hours, from 5pm to 10pm, one eats as much as possible in preparation for the next 19 hour fast. Water, herbal tea, black tea and black coffee are the only items consumed during the fasting period.
Tips to Safer Intermittent Fasting
It is important to drink plenty of water, even during fasting hours. Not only does this alleviate any possible hunger feelings, water stops dehydration and is essential to maintain good digestive health. Other non-sugary liquids such as black coffee and herbal teas are also safe to drink during fasting hours.
Exercise (if you can)
Many people are unsure whether it is safe to exercise while fasting. This varies from person to person and depends on your health circumstance. Exercising in a fasted state may decrease endurance and limit our ability to fully benefit from the exercise. If you find you run out of energy to exercise, you may require a change to your fasting pattern and increasing your energy intake.
Having a restricted eating window means that you may be missing out on fibre. Fibre is a key nutrient that helps normal digestion and keeps IBS symptoms at bay. Small meal portions that are high in fibre help you feel fuller for longer and reduce digestion complications.
Supplements and Medication
If you have any nutrient deficiencies or are on any medications, it is important to contact a General Physician or Dietitian before making any diet changes. Some medication and supplements are required to be taken with food, as they are less likely to be absorbed by the body on an empty stomach. If you do take supplements, it is a good idea to take them during non-fasting hours. This includes any fat-soluble vitamin supplements such as vitamin A, vitamin D, vitamin E and vitamin K.
What are the Benefits of Intermittent Fasting?
Intermittent fasting has been shown to be effective way to lose weight when closely followed. This is because fewer calories are consumed overall. Any eating plan with energy restriction for over a week may lead to weight loss; however this may not be sustainable long term. There is some research to support increased sports performance and other health benefits, however this research is very scarce.
Intermittent fasting is easy to follow and has very few rules. It is good for those with a busy lifestyle who may only eat out of obligation. Many people report feeling fuller for longer (after the adjustment period). The two main benefits are that it promotes choosing high quality proteins to fill up and nutritious foods such as fruit and vegetables, as well as eating one’s favourite foods which people miss out on with other diets.
What are the Cons of Intermittent Fasting?
While following an intermittent fasting diet has some potential benefits, there are certainly more downsides. It’s no surprise that intermittent fasting reduces the number of meals consumed. Because of this, nutrient deficiencies (fibre, vitamins, and minerals) can occur, particularly in people who regularly exercise or people who need to follow specialised diets.
A healthy diet of fruit, vegetables, grains, and legumes can increase mood and brain function. However, during fasting, energy and concentration levels can drop; there is potential for muscle mass loss; sport or training performance can drop and muscle recovery can be negatively affected.
Other drawbacks are intense hunger and mental-deprivation during the adjustment phase. This may lead to overeating during non-fasting hours. Not only may this contradict any potential benefits gained by intermittent fasting, but it may also lead to digestion issues.
People with IBS commonly experience an overactivity of the gastro-colic reflex in their digestive system after eating. The gastro-colic reflex is the wave-like movement muscles make to push food along our digestive tracts. When larger meals are eaten in a shorter time span, this sends the gastro-colic reflex into overdrive, which may trigger IBS symptoms. This usually follows a long fast, so the digestive system is not as used to larger food portions, as it would be if smaller more regular meals were eaten.
Can People with IBS Intermittent Fast?
There is currently no research that states intermittent fasting helps relieve IBS symptoms. Some people report less bloating and stomach cramps during fasting hours, though this may be because food is the main trigger for many common IBS symptoms. Therefore, stopping this trigger would naturally lessen IBS symptoms. During non-fasting hours, people tend to eat much more than usual. If you are following a low FODMAP diet, you may accidentally consume over the recommended amount of FODMAP safe foods, leading to painful IBS symptoms. As a first option to treat your IBS symptoms, it is a good idea to focus on eating more moderately sized meals which are high in fibre.
Who else should skip intermittent fasting?
If you are: pregnant, breastfeeding, underweight, under 18 years of age, deficient in any nutrients or have a history of or current eating disorder. These groups may be even more negatively impacted by restrictive eating or fasting, susceptible to nutrient deficiencies and require more energy for growth and development.
Take home message
Intermittent fasting might be an efficient way to lose weight, but not necessarily sustainable long term. Though the diet trend has shown potential benefits in healthy individuals, people with IBS or any other medical conditions should be wary. Fasting does not heal or reverse any IBS symptoms. Instead, aim to eat a healthy range of low FODMAP plant foods – fruits, vegetables, grains, legumes, and other foods high in fibre. It is also important to talk to a qualified Dietitian who can support you and offer a personalised approach if you choose to go down this pathway.
Written by Sara Weedon (Nutritionist)
Reviewed by Kiarra Martindale (Accredited Practising Dietitian)