In recent years, intermittent fasting has become increasingly popular. According to Google Trends, the number of online searches for ‘intermittent fasting’ has increased by 10,000 percent since 2010.
Supporters of the eating habit claim that fasting leads to weighloss and is more sustainable than traditional diets.
What is intermittent fasting?
Intermittent fasting is an eating pattern that cycles between periods of eating and fasting. There is no standard duration for fasting – it can range from a number of hours to a few days.
Fasting is not a new concept. Intermittent fasting has historically been present in human eating habits for a number of reasons, including as a result of food scarcity and for religious purposes such as Ramadan, Yom Kippur and Vrata. While supporters believe that fasting is more sustainable than traditional diets, many struggle to restrict their eating to smaller windows and the dropout rate for fasting is high.
How does intermittent fasting work?
The aim of fasting is to allow the body to use its stored energy to burn excess body fat. This process is a normal evolutionary trait in humans as excess body fat acts as reserved food energy. Therefore, not eating will cause your body to simply use its reserved fat energy.
The body exists in two states: fed and fasted. In the fed state, insulin is higher and food is stored as energy reserves. In the fasted state, insulin is lower and reserved energy is burned. The theory, therefore, is that when the two states are balanced, there should be no net weight change. Intermittent fasting is said to lose weight by keeping the body in the fasted state for longer.
Benefits to intermittent fasting can include:
- Fat loss
- Lowered blood insulin and sugar levels
- Reduced insulin resistance
- Reduced inflammation
- Increase in longevity.
Although certain benefits of caloric restriction have been demonstrated in animal studies, similar benefits of intermittent fasting in humans have not been observed. There is no concrete evidence that intermittent fasting is a better weight loss method than others when considering the amount of weight lost, compliance rates and decreases in appetite. While many benefits to fasting have been anecdotally observed, further long-term and randomised control trials are required to confirm health benefits and effectiveness of fasting.
House Call Doctor experts warn that all diets contain risks. Risks to intermittent fasting can include:
- Changes in mood
- Low energy
- Binge eating behaviour
- Obsessive thoughts about food.
There is some evidence that women do not benefit from intermittent fasting as well as men do. One study found women experienced worsened blood sugar control from fasting. Anecdotal reports have also shown menstrual cycles were affected during fasting but returned to normal when a regular eating pattern was adopted.
People who are underweight or have a history of eating disorders should not consider extreme dieting. Intermittent fasting is also not appropriate for those with conditions that require food at regular intervals due to metabolic changes caused by medications. This includes those with diabetes types 1 and 2, those taking medication that requires food consumption, and women who are pregnant or breastfeeding.
There are a number of methods to intermittent fasting:
The 16/8 Method
The 16/8 method involves fasting for 16 hours each day and restricting eating to an 8-hour window. This typically means two to three meals are consumed between 12pm and 8pm. It is important to note that women see more success with slightly shorter periods and are recommended to fast for 14-15 hours rather than 18.
The 5:2 Method
The 5:2 method involves eating normally for five days each week and restricting calories for two days. On restricted calorie days, women are recommended an intake of 500 calories and men are recommended 600.
This method involves a 24-hour fast either once or twice each week. It is important that you eat normally during the eat periods and eat the same amount as if you hadn’t been fasting, rather than binge eating because you are hungry.