Intermittent Fasting For Weight Loss and Improved Health

Although the act of fasting has been practiced for many years in religious and cultural settings, it has recently become popularised as an anti-aging and weight loss strategy by many health and fitness influencers. Fasting means to abstain from consuming food and drink for a given period of time. This in fact means that each of us fasts during the night when we sleep, and we break our fast in the morning when we eat breakfast, which is in fact when the name comes from. As mentioned in a previous post, this natural behaviour is governed by our circadian rhythm, which is responsible for preparing our body for food during the day and for rest at night.

Intermittent Fasting for Longevity

This period of allowing the body to rest and digest is a natural adaptation to our environment. It is during fasting that our body is able to repair and regenerate. The process responsible for this is known as autophagy, which can be summarised as the degradation and recycling of damaged proteins within our cells. This function is important for removing potentially problematic waste material that could damage cells and lead to improper functioning (1). For this reason, going without food for part of the day is promoted as a way to slow down ageing and is commonly referred to as intermittent fasting.

Intermittent Fasting: an Evolutionary Adaptation

The extension of this fasting widow assists the body in depleting its glucose stores in the form of glycogen in the liver and muscles and instead mobilise fatty acids from body fat as an alternative energy source. This process is called ketogenesis and is an evolutionary adaptation to times of scarcity of food. As pointed out by the paleoanthropologist Miki Ben-Dor, being able to fast for long periods of time was a necessity as larger and fattier animals were harder to come by (2). What’s interesting is that relying on fat for fuel, as opposed to carbohydrates found in food, helps to focus the mind and stabilise mood, which may have given humans an upper hand in search of food in the past. Nowadays, food is always available, which means these cognitive benefits are often not experienced, which is another reason why intermittent fasting is often promoted.

This improvement in cognition is due to the brain’s utilisation of ketones. Ketones are produced when your body is deprived of glucose and switches to using stored energy in the form of body fat as fuel. Ketones are considered as an alternative fuel source for the brain when glucose levels are low. As ketones are longer lasting and are not influenced by insulin levels, they provide a steady flow of energy to the brain. Increasing the brain’s ketone levels is thought to help mitigate cognitive decline in those suffering from early-stage dementia or cognitive impairment. As the underlying pathology of these conditions are linked to a decrease in glucose supply to the brain, intermittent fasting may have some benefits (3).

Intermittent Fasting for Weight Loss

Although intermittent fasting usually involves reducing one’s calorie intake for the day, as there is less time to eat, this is not the main reason it helps with weight loss. Instead, it is the condensing of food intake into a smaller time frame, typically 8 to 12 hours, which assists the body in burning fat and for this reason, its often called ‘time restrictive feeding’. For most people who practice intermittent fasting, eating three meals per day is still possible, and the same number of calories can be consumed. Multiple studies show that 8-12 hours of time restrictive feeding without intentional calorie restriction results in weight loss in both overweight and healthy participants (1). Although studies comparing intermittent fasting to a diet focusing on calorie restriction show similar levels of weight loss, intermittent fasting seems to have more of a beneficial effect on insulin sensitivity, meaning a reduced risk of diabetes and improved blood sugar regulation. This may explain why, at least anecdotally, many report feeling less hungry and more satiated when intermittent fasting as opposed to restricting their calorie intake. This is not surprising, considering that intermittent fasting is about adjusting your eating habits to align with your primordial physiology and therefore is a more sustainable way to lose weight.

Transitioning to eating within a specific timeframe can be challenging at first, which is why I recommend a wider eating window of 12 hours to start with. As your body begins to adapt, shortening your eating widow to 8 hours may be best if you are looking for faster weight loss. Discipline, at least initially, is needed and therefore it will help to stick to a regular eating schedule each day. So, for instance, you may decide not to eat 2-3 hours after you wake up and before you go to bed.

Intermittent Fasting for Gut Health

Intermittent fasting may help those who suffer from digestive symptoms. The absence of food provides time for your colon to heal and repair. This is particularly the case for those who experience inflammatory conditions such as inflammatory bowel disease and ulcerative colitis. This is because food aggravates the lining of the large intestine, leading to inflammation and discomfort. Mice models show that short periods of fasting help improve the integrity of the gut lining and reduce inflammation (4) (5). Studies looking at humans are few and far between, however.

Recent research reveals the bacteria that reside in the gut, which are collectively referred to as the gut microbiome, follow a circadian rhythm, as do the cells in our bodies. This means species diversity shifts during the day and night. Each species has a different role to play in relation to our health, which is why a healthy gut is generally one which is diverse (6). For instance, the key species akkermansia muciniphila is important for maintaining the health of the mucus lining that covers the large intestines. Without this protective layer the gut can become inflamed, leading to a plethora of health issues. This particular species has been shown to increase following periods of fasting, which is another reason why intermittent fasting may be helpful (7).

Intermittent fasting may also help those who experience constipation, with animal studies showing an increase in bile acid secretion following time-restrictive feeding (8). Bile is produced in the liver and stored in the gall bladder. Its job is to help lubricate the gut and assist the breakdown of fats and assimilation of fat-soluble nutrients such as vitamin A, D, E and K.

To summarise, implementing intermittent fasting into your life may help those looking to enhance weight loss alongside a change in diet. For those who suffer from chronic digestive problems, intermittent or extended fasting periods may have favourable outcomes as well as promoting longevity. Although it may seem challenging at first, with a little will power it won’t be long before you see the benefits and the discipline gained by this style of living, which may also carry over to other aspects of your life.