To fast or not to fast? All your questions about intermittent fasting, answered

Intermittent fasting is making waves in the wellness world, but beyond the hype what are the real advantages of time-restricted eating? We take a look at the dietary method to see if it’s really all it’s cracked up to be.

The term “intermittent fasting” has taken the wellness and dieting worlds by storm. Variations of calorie-restricted eating and fasting windows have been rising in popularity as both a weight-management tool and a long-term nutrition plan.

Touted as having health benefits ranging from weight loss to reduced inflammation and brain protection, it is no wonder that so many people have adopted the intermittent fasting trend.

With a growing abundance of books, apps, methods and even calorie-restricted dieting kits to support the dietary method, there is no doubt that intermittent fasting is here to stay.

Intermittent fasting is less about implementing a new way of eating and more about returning to the way humans consumed food for centuries.

Despite its popularity, many people are still mystified about the exact ins and outs of the method. Whether you are an experienced intermittent faster, have dabbled in it or are a total novice, you might be wondering if an eating pattern can really live up to such impressive claims. Or could it in fact have adverse consequences?

It’s worth noting that every person responds differently to nutrition, and there is never a one-size-fits-all answer.

Here we go beyond the intermittent fasting trend and delve deeper into the various methods, the pros and cons and who should steer clear of intermittent fasting.

What exactly is intermittent fasting?

One of the most confusing aspects about intermittent fasting (IF) is the many different forms it can take. A popular method is the 16:8 method, which involves fasting for 16 hours and consuming all meals and calories during the other eight hours in a 24-hour day. This could mean skipping breakfast, eating your first meal around midday and ensuring your last meal is finished by 8pm. For people who prefer to eat breakfast, the first meal could be consumed around 10am and dinner finished by 6pm. During the fasting period, water and low-calorie beverages such as black coffee and teas without milk or sugar added are generally allowed as they do not interrupt the fasting state of the body. Many people also find that this helps them feel satiated while in their fasting window.

Other commonly practised IF methods include the 5/2 Diet, where calorie intake is restricted to 500 calories a day during two days of the week and a normal healthy diet is consumed on the remaining days. Some prefer to implement a 24- to 36-hour fast once a week. The Fasting Mimicking Diet, which provides a five-day kit of nutritionally formulated foods to achieve the same benefits as traditional fasting, has also recently gained popularity in the IF world.

The benefits

What do all these methods have in common? Whichever form of IF appeals to you, they all promise the same highly desirable benefits, such as positively influencing longevity, improved heart health, weight loss and increased cellular repair processes. Research shows that periods of fasting can be used as an overall health tool to improve insulin sensitivity, irregular glucose levels, high blood pressure and disproportionate percentages of body fat, as well as reduce inflammation. IF has also been positively linked to a reduction in ectopic fat, which is the unhealthy fat that surrounds organs, typical of type-2 diabetes.

IF is less about implementing a new way of eating and more about returning to the way humans consumed food for centuries. The indulgent food culture of the modern world has given rise to many health complications and lifestyle diseases. As Dr Jason Fung, a proponent of the intermittent fasting movement, summarises in his book The Obesity Code: “This is the ancient secret. This is the cycle of life. Fasting follows feasting. Feasting follows fasting. Diets must be intermittent, not steady.”

The physiology of intermittent fasting

If all the perks of time-restricted eating sound almost too good to be true, a further exploration of the physiological mechanisms behind IF, namely ketosis and autophagy, will help illustrate how this dietary approach can yield such a plethora of covetable wellness benefits.

Ketosis
Ketosis is a natural metabolic state in which the body produces ketone bodies out of fat that are used as the body’s energy source, instead of carbohydrates. Glucose (blood sugar) from carbohydrates is the preferred fuel source for most cells in the body; however, by following a high-fat, very low carbohydrate “ketogenic diet” or through fasting, you can force your body to switch over into ketosis. Experts generally suggest you need to fast for a minimum of 12 hours in order to transition into this ketogenic metabolic state where you begin calling on ketone bodies (essentially molecules derived from fat) in conjunction with free fatty acids as the body’s primary fuel.

The presence of ketones may help to prevent the development of many chronic diseases through reducing oxidative stress and inflammation. In addition, research has shown that being in ketosis can regulate appetite, normalise blood sugar and insulin response and support weight loss.

Autophagy
Autophagy is a process activated further into periods of fasting, which triggers many of the remarkable health rewards attributed to fasting. Although autophagy has been on the radar since the 1960s, it was not until recent years that scientists have been able to study and understand it more closely. In 2016, Dr Yoshinori Ohsumi was awarded the Nobel Prize in Physiology and Medicine for his discoveries of the mechanisms for autophagy.

Practising IF as an eating pattern that includes regular, short-term fasts has become a popular lifestyle choice, propelled by the potential benefits such as weight loss, improved body composition, disease prevention, longevity and overall wellbeing.

The word itself is rooted in the Greek words auto-, meaning “self”, and phagein, meaning “to eat”, literally translating to “self-eating”. The process it describes is exactly that: an evolutionary self-preservation mechanism where your cells self-devour (or remove) damaged parts. It is essentially the key way the body instigates cellular and tissue regeneration, by cleaning out and recycling these damaged cellular components, such as misfolded proteins.

So what happens when your cells are unable to initiate autophagy? It seems to give rise to accelerated ageing and neurodegenerative diseases. Generally, the more we age, the more autophagy is reduced. That’s where the longevity aspects attributed to fasting come in. Fasting can be used to activate a pathway that inhibits what is called mTOR activity, which ultimately induces a state of autophagy. In order to achieve this result, however, glucose levels must begin to deplete substantially along with a significant drop in insulin levels.

According to the limited research available, you need to fast for at least 24 hours to experience deeper states of autophagy. In food-deprived mice, autophagy increases after 24 hours, with the full effect magnified in liver and brain cells at the 48-hour mark. In human studies, autophagy has been detected in neutrophils (a type of white blood cell that helps to heal damaged tissues, an important part of the immune response) once 24 hours of fasting is reached. Therefore, in order to reap the benefits of fasting-induced autophagy, you would need to follow one of the variations that involves longer fasting periods.

Potential downsides

Although it would seem that IF is a holy grail for weight loss and wellbeing, it’s important to explore the ways in which it can be detrimental to health and sustainable weight management for some individuals. Following any form of controlled diet can come with psychological consequences that may create a complex relationship with food.

Clinical nutritionist and author of The Healthy Life Jessica Sepel believes that fasting can cause people to feel restricted and deprived, which can be counter-intuitive for both physical and emotional wellbeing. As she explains, “Dieting with methods such as fasting often backfires with the other extremes of overeating or binge eating as the brain does not like to feel restricted.” So while from a research perspective there are clear benefits of fasting, Sepel says it’s important to assess whether IF is an approach that you can healthily maintain or whether it could in fact be encouraging an unhealthy relationship with food and your body.

Disordered eating, even without weight loss, has been associated with menstrual irregularities in females and secondary amenorrhea. Chronic dieting, fad dieting, fasting and skipping meals are all classified as unhealthy dieting strategies, so it is important to assess whether practising IF could cause some psychological issues.

On the flip side, some individuals may find that simply following a time-restricted eating regimen allows them the freedom from other dieting tropes such as counting calories or avoiding and limiting certain foods, and the pros of this may outweigh the cons.

Putting hormones in the equation

It is also important to consider that women and men have different bodily operating systems, due to hormones and composition, which can also influence whether IF is a suitable dietary protocol to follow. There is some evidence that IF may not be as beneficial for women as it is for men. One study actually showed that blood sugar control became worse in women after three weeks of IF, which was not reflected in men.

Following any form of controlled diet can come with psychological consequences that may create a complex relationship with food.

Especially for women in their reproductive years, it may be problematic as female bodies are very sensitive to calorie restriction. IF could potentially result in low calorie intake due to fasting for too long or too frequently, in turn affecting a part of the brain called the hypothalamus. This can disrupt a series of hormones essential for a healthily functioning reproductive system, including luteinising hormone (LH) and follicle-stimulating hormone (FSH). If communication between these reproductive hormones and the ovaries is interrupted, hypothalamic amenorrhoea (loss of menstrual periods) can ensue, as well as irregular cycles, infertility and lowered bone density.

Fasting and dieting in general could also cause both physical and psychological stress on the body, leading to a spike in cortisol, the stress hormone. A research study tested the hypothesis that dieting is not effective as it raises stress and cortisol production; it concluded that restricting calories raised total cortisol and simply monitoring calories increased perceived stress. Since all hormones work in connection to each another, this impacts the overall working of the endocrine system. So if you have struggled with irregular periods, it could be a sign that IF may not be well suited to you at this time of your life. “People struggling with period loss need to try to calm down the stress response and therefore fasting would not be ideal for their bodies,” explains Sepel.

A sustainable, balanced approach

Practising IF as an eating pattern that includes regular, short-term fasts has become a popular lifestyle choice, propelled by the potential benefits such as weight loss, improved body composition, disease prevention, longevity and overall wellbeing. The research certainly supports the positive results that fasting can have. However, you should always seek medical advice before starting a fasting program. Experts generally agree that there are some people who should not attempt intermittent fasting, such as children, the elderly and those with medical conditions, nutritional deficiencies or a history of eating disorders or who are underweight.

Other instances where IF may have adverse consequences are when it leads to or encourages an unhealthy relationship with food, is practised in a way that is unsustainable for you, or if you are a woman — especially if you are in your reproductive years. Unfortunately, there is not enough research available yet to draw any definitive conclusions; however, women who wish to follow a time-restricted eating lifestyle may benefit from choosing a modified approach to traditional forms of IF, such as shorter fasting periods (12 hours) or fewer fasting days.

We are all individual, and what works for you may be completely different from others’ experience. The pot of gold at the end of the rainbow isn’t about adhering to strict time frames and dietary rules, it’s about feeling great, enjoying life and thriving. Whatever tools you use to get there, tread cautiously, make sure they are sustainable and allow for balance in your life.