Is Fasting Good For You?
Fasting diets have shot to fame for their potential weight loss benefits - you've probably heard of the 5:2 diet which has been in and out of the news over recent years. However, the idea of fasting isn't a new fad or trend - while the weight loss benefits have grabbed most of the headlines, many people don't fast to lose weight. Instead, they fast to promote good general health or spiritual well-being.
While intermittent fasting is not for everyone, if you've struggled to stick to long-term calorie-restricted diets in the past, you may find fasting to be a useful tool to lose or maintain weight as it allows more control over your food choices. There is also plenty of evidence to show that, when done properly, intermittent fasting can reduce the risk of diseases such as diabetes and heart disease, and may even help you live longer.
What is Intermittent Fasting?
Solid fasting or long-term low-calorie diets are not particularly beneficial for health. Eventually, the body's metabolism slows down to preserve energy in response to the reduced calorie intake. When the diet ends and calorie intake increases, the metabolism takes a while to recover and any weight loss often goes straight back on. In contrast to this, intermittent fasting involves cutting back on calories for much shorter periods of time, which means that the body never becomes accustomed to the lower calorie intake.
There are different methods of intermittent fasting so it's important to find an eating pattern that suits your lifestyle:
- Daily – This involves fasting for around 16 hours every single day. You consume no food during fast hours and eat a normal diet during the eight non-fast hours. Many people find that extending the overnight fast by skipping breakfast (or eating it later in the morning) is the easiest way to do this. Water, coffee and tea are fine during the fast, as long as they contain no milk or sugar.
- Weekly – The 5:2 diet is perhaps the best known, which involves fasting for two nonconsecutive days each week. You eat a normal diet five days of the week and then restrict your calorie intake to 25% on fast days - 500 calories for women and 600 calories for men. Another option is alternate day fasting, which reduces calorie intake to 25% every other day.
What Happens When You Fast?
When you are fully fed, it can be hard for the body to burn fat because insulin levels are typically high for three to five hours after eating. When the body is deprived of food for more than eight hours, blood insulin levels drop and the body starts to break down and burn stored fat to produce energy. Fasting also increases the release of human growth hormone, which further facilitates fat burning and muscle gain.
Technically we all fast at night when we sleep. We go around eight hours without food, which is plenty of time for the body to absorb all the nutrients from the previous meal. But increasing this period to at least fourteen hours may improve the body's fat burning potential. The initial transition to fasting can be a jolt to the system, leaving you feeling grouchy, low on energy, and hungry. The body is used to receiving food every few hours so fasting involves retraining your brain.
Over time (often within a few days or weeks) your body will become accustomed to fast days and will continue to function at its optimal level with regards to cognitive performance, activity levels, energy levels, sleep, and mood.
The Benefits of Fasting
Many supporters of fasting claim that from an evolutionary standpoint, our bodies are designed for periodic cycles of feast and famine, as our ancestors didn't eat three square meals a day. And there is now compelling evidence to suggest that periods of fasting can be good for health.
May Promote Weight Loss
In addition to the obvious benefit of consuming fewer meals and calories, intermittent fasting also helps the body to burn through fat cells more effectively. It increases the body's metabolic rate by lowering insulin levels and increasing growth hormone levels, which means that the body uses fat as its primary source of energy instead of sugar. This enhanced hormone function facilitates weight loss.
A review in 2014 found that intermittent fasting accelerated weight loss by as much as 8% over a 3 to 24 week period, particularly belly fat, which is the most harmful type of fat. The review also found that intermittent fasting resulted in less muscle loss than constant calorie restriction, which is why many athletes use it to reach low body fat percentages and a lean body. Other studies have found that daily intermittent fasting can result in significant weight loss despite the same daily calorie intake. Participants simply ate all their calories within an eight-hour window as opposed to spreading over the whole day.
May Lower the Risk of Diabetes
Intermittent fasting lowers insulin levels and blood sugar levels and so may offer some protection against type 2 diabetes. Studies show that intermittent fasting can reduce fasting blood sugar levels by 3% to 6%, and fasting insulin by 20% to 31%. This is because intermittent fasting helps the body to tolerate carbohydrates better. If you suffer from or are at risk of type 2 diabetes then please consult with a medical professional before trying a fasting diet.
May Help Your Heart
Intermittent fasting has a beneficial effect on several markers of heart disease including blood pressure, cholesterol levels, triglycerides, and blood sugar levels. There is human evidence to suggest that it reduces the build-up of fatty plaques along blood vessel walls and lower the risk of clogged arteries. However, further study is needed.
May Reduce Inflammation
A certain amount of inflammation is needed to repair damage in the body. However, when inflammation becomes chronic, it can increase the risk of asthma, allergies, autoimmune disease, heart disease, cancer and many other diseases. Poor diet and an overworked digestive system are two common causes of chronic inflammation, and intermittent fasting has been shown to reduce the number of inflammatory markers they cause.
A couple of large scales studies have found 12-hour fasting - fasting from noon to night – significantly reduced markers of inflammation, including interleukin-6 (IL-6), C-reactive protein (CRP) and homocysteine levels during the fast, which lasted for around twenty days after the fasting period. During the studies, there was no difference in caloric intake between the individuals fasting and the control group. When the fasting group was free to eat, they consumed as many calories as the group eating three meals a day. Therefore, it was fasting that reduced inflammation rather than calorie restriction.
May Increase Brain Function
When the brain is overfed, it can experience uncontrolled excitation, which impairs its function. Many nutrition experts believe that fasting improves cognitive function due to the neurochemical changes that occur in the brain when we fast. It is thought that that fasting shifts stem cells from a dormant state to a state of cell renewal and enhances the ability of nerve cells to repair DNA.
May Improve Energy Levels
Many of the body's toxins are stored in fat cells, which are dissolved and removed from the body during fasting. This process helps to rejuvenate and repair the body and boost energy levels.
May Extend Your Lifespan
There is a belief that the less you eat, the longer you live. The theory goes that a higher food intake leads to a higher metabolic rate, which increases energy expenditure by the body, leading to quicker ‘wear and tear' and a shortening of the lifespan. Basically, the more we eat, the harder our bodies have to work.
During fasting, the body goes into a cleansing phase that destroys old damaged cells and stimulates the production of new cells through the release of human growth hormone. This generates healthier neurons and better communication processes, and potentially increases the body's resistance to age-related diseases. While there is extensive animal-based research to support this theory, more human data is needed before we can say conclusively that intermittent fasting delays ageing in humans.
How Often Should You Fast?
Choosing a time or day of the week to fast is specific to the individual. Some people fast by avoiding food completely for certain periods every day such as from 8 pm to 12 pm the following day. Others choose to limit their calorie intake for an entire day. Some people find it easier to fast on busy work days when they are constantly distracted from food. Others find that fasting zaps valuable energy on these demanding days, and so opt to fast at the weekend when they can relax and reduce their energy expenditure.
In order for fasting to be effective, you need to find the right balance. If you fast too often, you risk depriving the body of certain nutrients and fasting yourself into depletion. If you don't fast enough, you won't feel the benefits. Generally, the longer the fast, the longer the recovery period needed before the next one. If you fast for 16 hours, you can then you should be safe to fast daily. If you fast for 24 hours, you should wait at least another 24 hours before starting your next fast.
Most importantly, listen to your body. If you constantly feel exhausted and lethargic, chances are you are doing too much. Fasting diets are fairly simple and straightforward when you learn how much you can eat on fast days, and many people find they provide much more freedom than long-term calorie-restricted diets. Plus, they are flexible; if something comes up and you miss a fast day, reschedule it for later in the week.
On fast days, eat foods that are high in protein and fibre such as fish, meat, veggies as these are the most filling. Staying well hydrated will make your fast days easier to get through. Water, tea and coffee are all fine but bear in mind that added milk, sugar or juice concentrates all add to your calorie intake. It's important to avoid refined carbs and sugars, as these are particularly calorific.
Can Fasting be Dangerous?
Many of the potential dangers aren't specific to fasting but apply to abusing dieting and exercise in general. Intermittent fasting appears to be appropriate for most people. However, some people should seek medical advice before starting a fast diet, including pregnant women, diabetics, those with low blood pressure, those with an eating disorder, those with thyroid disorders, and those taking prescription medications. Women of a healthy weight who are trying to maximise fertility are also advised to avoid fasting.
Some experts warn that fasting shouldn't be the first step to weight loss as it may make people too relaxed about eating healthily during non-fast periods. Instead, individuals should focus on eating a healthy and balanced diet first. If you choose to fast, then it's important to do so sensibly, as if you fast for too long, the body may start to break down muscle proteins to create energy.
If you eat a balanced diet on non-fast days, then intermittent fasting should be safe. However, if you use non-fast days as an opportunity to indulge in vast amounts of unhealthy foods then it is unlikely to offer any health benefits. The yo-yo effect of going from a strict fasting diet to a diet rich in processed fatty foods can be hard on the body and have negative outcomes such as headaches, moodiness, and difficulty concentrating. Also, don't eat a calorie-restricted diet on non-fast days.
Whilst you shouldn't overindulge, it can be dangerous if you are already dieting and cutting your calorie intake. For a healthy fast, you should ensure that non-fast days are packed with antioxidant-rich fruit and vegetables, protein, good fats, and whole grains.
Is Fasting the Right Choice for You?
Fasting is not a diet but a pattern of eating that can have incredible benefits when done sensibly, particularly for weight management, blood glucose levels, and heart function. Evidence shows that intermittent fasters lose more weight than those on long-term low-calorie diets, retain more muscle mass, and see improvements to glucose levels. Plus, it also counteracts the negative inflammatory effects of constantly snacking between meals.
Fasting can be much easier than dieting. You don't have to follow a strict diet every day of the week, which many people find easier to maintain long term. It shouldn't really change what you eat, it just changes when you eat them, so you can still eat out and dine with friends without too much concern for your calorie intake. However, fasting isn't a magic pill. If you generally eat poorly and do little exercise, you can't expect fasting to solve all your problems. In reality, you will see the best benefits when you adopt a balanced approach to food, making healthier food choices every time you eat.