Updated: Jan 2
It may seem that intermittent fasting is a recent health trend, however, it has actually been used since the beginning of time, and may have been used as an ancient secret to good health.
What is intermittent fasting?
Intermittent fasting is a way of eating that switches between incorporating extended time periods with no food intake, typically between 16 and 48 hours, with periods of normal food intake, on a recurring basis.
There are different forms of fasting, which all come under the definition of abstinence or limitation of food and/or drink.
Intermittent fasting is different from time restricted fasting, which is where a person refrains from eating, generally for a 16-hour window, and eats during the remaining 8 hours. This method is otherwise known as the 16:8 diet. Whereas an example of intermittent fasting is the 5:2 diet, which entails eating less than 500 calories for two days a week, consecutively or non-consecutively. Both of these diets have been shown to be beneficial for weight loss, blood sugar regulation, and reducing inflammation.
Other forms of fasting include prolonged or periodic fasting, which can be less than 3 days (short-term), or prolonged fasting (more than 3 days), which is thought to have anti-ageing effects.
Our ancestral predecessors learned to function at a high level, for long periods of time in a fasted state, because food was scarce. They adapted to their environment, with physical and cognitive benefits. This is quite unlike modern humans, who typically eat at least three times a day.
This overconsumption of food can very often lead to metabolic dysfunction, including weight gain, and insulin resistance, particularly when it’s associated with a sedentary lifestyle (1).
Some studies show that intermittent fasting can have profound beneficial effects on health, and most importantly weight loss, preventing diabetes and cardiovascular disease (2).
Furthermore, animal studies have shown that intermittent fasting can counteract disease processes such as cancer, stroke, Alzheimer’s disease and Parkinson’s disease (1), unfortunately though, human studies are sparse.
A more recent randomised controlled trial (2018) on human subjects with Multiple Sclerosis found beneficial changes in immune inflammatory parameters and gut flora in the fasting group. Interestingly, this study indicated that the beneficial effects were in part due to changes to the gut microbiome (3).
Another reported health benefit of fasting is that it can trigger autophagy. Autophagy is an innate immune system process of breaking down and removing old and damaged cells, to be recycled for energy. The word autophagy literally means to eat oneself. This process has been found to restrict viral infections and remove pathogens and cancerous cells, as well as protecting the body from toxicity and chronic inflammation (4).
How does intermittent fasting help with weight loss?
Without a supply of glucose to burn, the body is forced to use up its’ glucose stores, namely glycogen, which is mainly stored in the liver and muscle cells. As these stores go down, our body starts burning its' own fat for fuel and begins to produce ketones, the body’s alternative energy source.
When this process occurs regularly, we become fat adapted, which is our body’s ability to burn fat on a regular basis. This helps with metabolic flexibility, meaning that we can switch between burning glucose from carbohydrates, to burning fat when we are not consuming carbohydrates. An increased metabolic rate ultimately leads to fat and weight loss.
The benefits from fasting won’t usually be immediate as it is necessary for our bodies to adapt to fasting, which may take a week or two of intermittent fasting. What is important is that when you finish your fast, you eat a nutrient dense meal. Don’t expect to experience health benefits if you are bingeing on junk food after your fast.
Intermittent fasting alone won't necessarily help those with diabetes, it's important that they are consuming a low carbohydrate diet and incorporating daily exercise before embarking on a fast.
While fasting may help a large number of people with reducing inflammation and chronic disease processes, there are certain population groups where fasting may not be the best strategy.
· Anyone with a history of eating disorders
· Pregnant and breastfeeding women
· Young children
· Type 1 Diabetics
· Anyone who is severely underweight
· Those on certain medications
Always consult a healthcare professional before embarking on a fasting diet.
1. Mattson et al. 2017. Impact of intermittent fasting on health and disease processes. Ageing Research Reviews. doi: 10.1016/j.arr.2016.10.005.
2. Horne, B.D., Muhlestein, J.B. & Anderson, J.L., 2015. Health effects of intermittent fasting: Hormesis or harm? A systematic review. American Journal of Clinical Nutrition.
3. Cignarella et al. (2018) ‘Intermittent Fasting Confers Protection in CNS Autoimmunity by Altering the Gut Microbiota’, Cell Metabolism. doi: 10.1016/j.cmet.2018.05.006.
4. Alirezaei et al. (2010) ‘Short-term fasting induces profound neuronal autophagy’, Autophagy. doi: 10.4161/auto.6.6.12376.