Intermittent fasting (IF) is one of the most popular diets going round at the moment. From celebrities to athletes to every day people, many are raving about the benefits of intermittent fasting! But what exactly is intermittent fasting? And are there any real benefits?

Let's go back in time to when our ancestors didn't consume your typical three meals a day. Instead they would have wait for their next meal based on their environmental circumstances. They could perhaps go hours, days, or weeks without a meal. Fast-forward to 2020 and you will typically find westerners eating a regular, timely spaced 3 meals a day. But has this change in eating patterns hindered some of the beneficial roles of fasting in the body?

1. How does intermittent fasting work?

Predominantly in western diet, the cells in our body primarily use glucose (sugar) from carbohydrates as our main fuel source. However, when we fast we switch from using glucose to using fatty acids and ketones (fats) for fuel. Ketones are not just fuel used during periods of fasting; they are potent signalling molecules with major effects on cell and organ functions that influence health and ageing (1). Fasting periods can induce increased anti-oxidant effects, improved stress response, DNA repair, and reduce inflammation (2).

2. How to do intermittent fasting?

One of the most popular types of intermittent fasting is by eating within an 8-hour window, with the other 16 hours of the day considered to be in a ‘fasted’ state. For example, your 8-hour window starts at midday and finishes at 8 pm, outside of those hours you would be considered fasting (even if you’re sleeping!). There are also other popular types of intermittent fasting such as the 5:2 diet and alternate day fasting.

3. Intermittent fasting and longevity

One of the major claims of intermittent fasting is that it can increase lifespan. While this claim has been found in some studies, this has mostly been in studies involving mice and rats. One of the reasons why intermittent fasting may have had these results is believed to be that these rats and mice where in a calorie restriction (eating less food than required) (3). Whether it’s caloric restriction or intermittent fasting that may increase longevity is still a hot debate and it’s still too early to say for sure! (4).

4. Intermittent fasting and weight loss

You’ve probably met someone recently bragging about how they’ve lost so much weight doing intermittent fasting… is this some kind of magical fat loss diet? A study of young men who fast daily for 16 hours lost fat while maintaining muscle mass during 2 months of resistance training (5), while another study of 16 healthy participants also saw a reduction in weight and fat mass over 22 days (6). What could explain these results? When you intermittent fast this can improve insulin sensitivity and can result in less food cravings or naturally eating less. Furthermore, by eating in a time restricted frame you may just naturally eat less! 

5. Intermittent fasting and brain health

One of the interesting effects of intermittent fasting is on brain health. Studies in humans have confirmed that intermittent fasting can enhance both brain function and memory (7). This is an interesting notion, as a decline in brain health in part of ageing and could be used as a potential intervention in older adults. Intermittent fasting has also showed positive benefits in neurodegenerative conditions such as Alzheimer’s disease and Parkinson’s disease (8).

6. Intermittent fasting, diabetes and heart disease

As we previously mentioned, intermittent fasting can help to improve insulin sensitivity. Insulin sensitivity is a strong indicator of the development of diabetes. Low rates of both obesity and diabetes have been found in the island of Okinawa where they participate in intermittent fasting as part of their culture (9). Another two recent studies showed that daily caloric restriction or intermittent fasting reversed insulin resistance in patients with prediabetes or type 2 diabetes (10) (11).

Intermittent fasting has also been found to improve multiple indicators of heart disease such as blood pressure, heart rate and cholesterol levels (12)!

7. Intermittent fasting and inflammation

Many chronic health conditions are characterised inflammation. Interestingly, intermittent fasting has demonstrated to have anti-inflammatory properties (13). In the case of multiple sclerosis (MS), intermittent fasting managed to reduce symptoms in as little as two months (14). Based on these results, it’s been suggested that intermittent fasting could be beneficial in other autoimmune conditions such as rheumatoid arthritis.

The bottom line?

Intermittent fasting has shown to have many benefits for many health conditions such as obesity, diabetes, heart disease, cancers and brain health. However, many of these results have typically been found in animal studies, and are typically short-term.  We are still learning about exactly how these intermittent fasting can produce these results. In saying that, intermittent fasting is relatively safe and could prove to be beneficial for human health and certain conditions. Just remember that a diet that works for one person may not work for another.

References:

1. https://pubmed.ncbi.nlm.nih.gov/28826372/
2. https://pubmed.ncbi.nlm.nih.gov/21840335/
3. https://pubmed.ncbi.nlm.nih.gov/21388497/
4. https://www.nature.com/articles/ncomms14063
5. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-016-1044-0
6. https://pubmed.ncbi.nlm.nih.gov/15640462/
7. https://pubmed.ncbi.nlm.nih.gov/19171901/
8. https://pubmed.ncbi.nlm.nih.gov/29321682/
9. https://www.researchgate.net/publication/6973476_Caloric_restriction_and_human_longevity_What_can_we_learn_from_the_Okinawans
10. https://casereports.bmj.com/content/2018/bcr-2017-221854
11. https://pubmed.ncbi.nlm.nih.gov/29754952/
12. https://www.nejm.org/doi/full/10.1056/nejmra1905136
13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1859864/
14. https://pubmed.ncbi.nlm.nih.gov/27239035/