Intermittent Fasting: What Effect Does It Have on Health, Weight Loss or Sports Performance and Who Is It Good For?

Intermittent fasting is a way of eating in which periods of fasting and eating alternate throughout the day. It has built up a good reputation, especially as an effective and quick way of losing weight, which can easily lead you to the figure of your dreams. In addition, its positive effects on the brain, concentration or better control of hunger or blood sugar (glycaemia) are also said to be beneficial. Is intermittent fasting right for you if the traditional way of eating or losing weight does not suit you? And what else can you gain from intermittent fasting?

In this article you will read about the positive impact of intermittent fasting on these specific areas:

In this article you will also read about the negative impact of intermittent fasting on these specific areas:

What is intermittent fasting?

Intermittent fasting (IF) is a way of eating that alternates periods of fasting for different lengths of time with periods of eating. In fact, it is possible that you may be practising it yourself and not even know it. For example, if you skip breakfast and do not have your first meal until around lunchtime, this is a form of intermittent fasting.

In fact, this form is not unknown to mankind today. Your ancestors did not have food available all the time, as is the case today. They ate at times when they hunted or gathered it, and the intervals between meals were disproportionately longer compared to what you are used to today. At the same time, fasting is also known of in many religions.

Today, even though there is no longer a need to hunt for food and no spiritual reasons for fasting, there is a gradual return to a form of less frequent eating. Intermittent fasting is gaining popularity mainly because of its promising health benefits. Not only is it proving to be an effective method of weight loss, but it is also being used to improve blood sugar levels or pave the way to longevity.

What forms of intermittent fasting are known to us?

1. Alternate-Day Fasting – ADF

It is a form of intermittent fasting in which days of fasting and normal food consumption alternate daily. Thus, one day is spent fasting and the next day is spent eating a normal diet throughout the day. These days are repeated regularly. The fasting days can be moderated by consuming 25% of your normal daily calorie intake. ^[1]

2. Twice-Weekly Fasting – TWF

It is practically a full-day fast for two days a week. It is also known as the 5:2 fast. These can be any day you choose, and they may or may not be consecutive. As in the previous case, it is possible to consume 25% of your normal energy intake on the days designated for fasting. ^[1]

3. Time-limited intermittent fasting within one day

This form is perhaps the best known and most popular. It is not based on all-day fasting, but on time windows that are set aside for food intake and fasting. Within 24 hours, typically 16-20 hours are set aside for fasting and in the remaining 4-8 hours it is possible to eat. Within this short period of time, it is desirable to take in your daily optimal amount of calories and nutrients. Since this is the most common form, it is the one we will address later in this article.

The most common form is the 16:8 protocol, where you fast for 16 hours and can consume food for 8 hours. Into which part of the day you spread these hours depends on your preferences.

• You can start your day with breakfast, have your last meal in the afternoon and not eat any food until the next morning.
• On the other hand, you can skip breakfast and snacks, and start with lunch, for example, and eat until evening. ^[1]

Your chronotype will help you choose the right approach. If you’re an owl and like to sleep in the morning and live in the evening, it may be better for you to indulge in your first meal later in the day. Early birds, on the other hand, seem to be more appreciative of a hearty breakfast and limiting their meals to later in the afternoon. For one thing, it will be easier for you to control hunger, but your body and digestive system will also appreciate it if you adjust your food intake to your daily routine.

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How does intermittent fasting work?

Intermittent fasting is also popular for its simplicity. It sets precise boundaries for when foods can be eaten and when they can no longer be eaten. It focuses more on the timing of food consumption than on the choice of food. When used for weight loss, it helps to limit food intake so that it is easier to achieve a calorie deficit. You simply can’t fit as much food into eight hours as you eat in an entire day. Of course, a properly planned healthy diet is also important in this case. With sweets, sweetened drinks and other highly processed foods, it is very easy for you to exceed your optimum daily energy intake, even in those short eight hours. So even with intermittent fasting, in order to lose weight, you need to burn more calories per day than you take in.

Research shows that this way of eating also affects hormone production and function. For example, it leads to lower insulin levels, which can alleviate insulin resistance and therefore control blood sugar levels. There is also an increase in adiponectin, which is a hormone that helps increase tissue sensitivity to insulin. These and other changes in hormone levels are consequently responsible for many of the benefits associated with intermittent fasting. ^[14]

What are the health benefits of intermittent fasting?

1. Can facilitate weight loss

Dieting and calorie deficit can sometimes make you really uncomfortable. Weight loss often fails because the amount of calories allowed is too low, food portions are too small and the day is endlessly long. Hunger haunts you and it is difficult to stick to a diet. It is possible that you too have tried different ways to lose weight, but they have all failed.

Intermittent fasting is not a miracle method that will help you shed kilograms magically. However, in its own way, it can make losing weight easier. By cramming your daily intake into a smaller portion of the day, you’ll be able to indulge in larger portions of food. These can help you fight off hunger more effectively and keep you feeling fuller for longer. If you’re also one of those people who prefer a lesser frequency between meals and larger portions, intermittent fasting could just do you a world of good for weight loss. ^[9]

2. Assists to reduce hunger and cravings

It is not only during dieting that people are often haunted by hunger and never-ending sweet cravings. This can be caused by an incorrectly formulated diet, but also by inappropriate distribution of meals. As always, it is individual. However, many people, of which you may be one, have the experience that cravings and hunger are worse when food is spread out over the day. So naturally they try to look for a more functional plan for them.

This is where intermittent fasting appears to be able to help with this problem. For example, it may lead to an increase in peptide YY. This is a hormone that is secreted in the digestive system in response to food intake and triggers feelings of satiety. It also seems to reduce levels of ghrelin, the hormone that signals hunger. The combination of these factors thus leads to less hunger and a greater feeling of satiety after eating. ^[13,17]

Research is largely in agreement that to control appetite as effectively as possible, it is preferable to reserve a window of time for food intake earlier in the day. Have breakfast as your first meal and start fasting in the afternoon. This is probably related to the body’s circadian rhythms. These are processes in the body that repeat daily and are influenced by the alternation of day and night. This is how the performance of the digestive system or the levels of certain hormones change, for example. If you start eating in the morning and have your last meal in the afternoon, you are adapting your food intake to these natural rhythms more than if you started eating at lunch and finished in the evening. In this way, you can learn to better control your hunger and appetite. However, this is not a rule, and again, something different may suit everyone. You’ll do best to try out for yourself which option is right for you. ^[13,17]

If you are regularly plagued by sweet cravings and would appreciate tips on how to get rid of them, don’t pass over our article How to Get Rid of Constant Hunger and Cravings? 

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3. Affects blood sugar levels

Are you haunted by sweet cravings or constantly plagued by a lack of energy? This can also be a sign of blood sugar (glycaemia) fluctuations. These are not just exclusive to diabetics, but can also make life unpleasant for healthy people. When glycaemia is not under control, it can drop sharply. Then the body loses an immediate fuel load, which manifests itself in a feeling of lack of energy. At the same time, cravings for sweets appear as the body naturally wants to replenish these stores quickly.

It turns out that intermittent fasting is one way that could help keep blood sugar levels in check. This is because it promotes the movement of glucose from the blood to the muscles and other parts of the body, or helps the body store glucose more efficiently as glycogen. ^[9,19]

People with type 2 diabetes or those who have prediabetes (a precursor to diabetes) may also benefit from this diet. It has also been observed in studies that this restricted dietary intake leads to lower insulin secretion. This may help improve insulin sensitivity, leading to better glycaemic control overall. ^[12]

4. Positive effect on cardiovascular health

Cardiovascular disease is the leading cause of death worldwide. People commonly suffer myocardial infarction, stroke or ischaemic heart disease (a condition where the heart is not sufficiently coagulated). At the origin of these problems is atherosclerosis, in which cholesterol and various blood components build up in the blood vessel wall. This causes it to thicken and gradually clog the blood vessels. You also know that if you want to live to a ripe old age, you need to take care of your heart and blood vessels. It is thus important to prevent high cholesterol or blood pressure.

Today, it is known that a diet with adequate calories, plenty of unsaturated fats or fibre will help you. Conversely, you should limit highly processed foods full of sugar, salt or trans fats. However, intermittent fasting also has a positive effect on cardiovascular health. For example, studies describe a positive effect on lowering blood pressure, LDL (bad) cholesterol or triacylglycerols in the blood. In addition, a reduction in pro-inflammatory substances, which also contribute to atherosclerosis, has also been observed. ^[11,17]

5. It has an anti-carcinogenic effect

Cancer is the second leading cause of death after cardiovascular disease, with breast and lung cancer being the most common. A number of factors are involved in the development of these diseases, including those beyond your control, such as genetics or environmental influences. However, several others, including nutrition, are in your hands. By changing them, you will certainly do well to try to reduce your risk of developing cancer as much as possible. ^[4]

Sources suggest that intermittent fasting could help. In fact, thanks to several mechanisms, it has promising anti-carcinogenic properties. For example, its anti-inflammatory effects, possible support for the immune system or the alleviation of oxidative stress play a role in this. Some studies even suggest that intermittent fasting could increase sensitivity to chemotherapy in an already ongoing disease. However, the evidence is far from clear-cut and it is still the case that a person with cancer should follow a nutrient-rich diet. ^[14,16]

6. It affects the brain and cognitive function

Who wouldn’t want to have a healthy and efficient brain? In this day and age, when people face more and more pressure to perform, this demand is all the more pressing. Thus, people try to look for ways to improve concentration and memory or to keep their brains functional and healthy for as long as possible.

Interestingly, studies looking at intermittent fasting also observe these positive effects when it is being followed. It turns out that it can help improve or maintain cognitive functions such as the ability to learn or the aforementioned memory and concentration. There are several mechanisms of action behind this effect. One of these is the so-called metabolic switch, which can occur after prolonged fasting.

This is a phenomenon in which the body begins to prefer fat as a source of energy over glucose (which is the body’s natural preference). When this occurs, the fats are further converted down to ketone bodies, which become a source of energy for the brain during fasting. In addition, they are also involved in the function of brain neurotrophic factor, which is important for the protection and resilience of nerve cells. They are also involved in neuronal plasticity, which is essential for learning and memory. IF may thus be a way to kick-start these brain functions. ^[6] 

Research has also reported the positive effect of intermittent fasting on the risk of developing neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease. This way of eating could thus serve to help prevent these health problems in old age. ^[2,6]

If you want to do more for your brain’s performance, read our article Nootropics: Substances to Improve Concentration and Memory. Which are the best?

7. Has anti-ageing properties

The anti-ageing approach together with the concept of healthy ageing are becoming more and more important. In fact, life expectancy has almost doubled over the last century. Hand in hand with this, however, has come an increase in the incidence of age-related diseases. Today, virtually everyone will encounter some form of cardiovascular, neurodegenerative or, for example, cancer in old age. So many people are trying to look after themselves so that these problems can be prevented as much as possible. Moreover, everybody desires to be not only healthy, but also forever beautiful and ideally young. While nothing can guarantee eternal youth and health, there are ways to help you reduce the signs of ageing.

Intermittent fasting seems to be one such helper. For example, it has been shown to reduce oxidative stress, which is implicated in the development of various chronic diseases. It can apparently help with protection against brain damage or, for example, metabolic diseases (e.g. type 2 diabetes) that appear with age. As part of prevention against various health problems, this is one way that could help you age with better health. ^[9]

If you are interested in learning more about how to stay healthy for as long as possible, don’t miss our article Anti-Ageing and Healthy Ageing: How to Take Care of Your Body and Stay Healthy and Youthful? 

8. Has a positive effect on women’s health

A healthy and happy female body is largely related to healthy levels of sex hormones. These influence a myriad of physiological functions, and if their levels are disturbed, they make themselves known through health problems. One such inconvenience that is caused by an imbalance of female sex hormones is polycystic ovary syndrome (PCOS). Women with this condition have excessive levels of the female sex hormone oestrogen, but also of the male sex hormone androgens. This manifests itself with excessive body hair, acne or amenorrhoea (skipping periods), for example.

Research shows that intermittent fasting may also have a role in PCOS therapy. Results of studies conducted so far suggest that it may lead to a reduction in oestrogen and androgens. Although this effect would be undesirable in healthy people, in PCOS, when these hormones are in excess, it is an effect that may help to alleviate the symptoms of the disease.

Being overweight or obese usually goes hand in hand with PCOS, along with insulin resistance. As we have already discussed, these are also problems for which intermittent fasting can have a positive effect. If this is a condition that is troubling you, changing your diet might be worth a try. However, it is always advisable to consult a doctor and nutritionist before embarking on such a change. ^[3]

Does intermittent fasting have an adverse effect on health?

1. May impair sports performance

The effect of a particular dietary pattern on sports performance depends on the type of activity, its duration or intensity. This is also true for intermittent fasting, which has a different effect on endurance athletes compared to strength athletes. In general, however, this type of dieting has been shown to have a rather negative effect on sports performance.

What effect does it have on different types of sports?

• From studies done so far, it seems that if you are into bodybuilding, triathlon, weightlifting or other strength disciplines, intermittent fasting is not the ideal way of eating for you. In fact, it turns out that not only does it not lead to better performance, but it can actually make it worse.^[8]
• In high-intensity sports such as sprinting, the negative effects of intermittent fasting have been observed. This is because in this type of sport the body is dependent on the immediate availability of a carbohydrate load, which is often not available in IF. ^[8]
• Even in endurance sports, there is a deterioration in performance. Thus, IF can negatively affect, for example, running, cycling or swimming. However, some studies report a slight improvement in performance after a prolonged period of intermittent fasting. Thus, researchers hypothesise that the body may adapt and draw energy primarily from fat stores after a period of time. However, there are not yet enough studies to confirm that intermittent fasting actually has this effect in endurance sports. In general, however, during aerobic exercise, you get more energy per unit of oxygen from carbohydrates than you do from fat. ^[8,10,20]

2. Complicates the building of muscle mass

Available research finds that intermittent fasting is not the ideal way to eat when trying to build muscle mass. In fact, today’s recommendations tell you that you need to consume sufficient calories and protein to grow muscle. A daily dose of protein should range from 1.6 – 2 g/kg body weight. It is best to consume a dose of 20 – 40 g of protein every 3 – 4 hours in order to best promote proteosynthesis (the formation of new body proteins).

You can meet these requirements with a conventional diet, but intermittent fasting does not allow you to spread your protein intake evenly throughout the day. Moreover, it is quite complicated to take in a complete daily dose of protein within the time window allotted for food intake. Thus, according to today’s knowledge, it seems that if you want to achieve maximum muscle growth, it is preferable to choose a different dietary path. ^[7,8]

3. At risk of inadequate energy and nutrient intake

Although there are fewer hours of food intake with intermittent fasting, your body still needs the same amount of energy, protein, carbohydrates, fats or vitamins and minerals. Long-term deficiencies of these nutrients could lead to unhealthy weight loss, muscle loss, excessive fatigue or a range of health problems associated with nutritional deficiencies (such as weakened immunity due to vitamin deficiencies). Therefore, it is important to have a good plan in place to ensure that your diet is of a good quality and balanced, even with this way of eating.

4. Negatively affects testosterone levels

Testosterone is the main male sex hormone that is important for sperm production, muscle growth, libido, and other functions of the male body. Its optimal level is thus essential for male health. Intermittent fasting, however, has been shown to be able to reduce the production of this hormone, even with both short-term and long-term experiences with this dietary regimen. ^[3]

5. Increases the risk of hypoglycaemia

If you are not used to restricting your food intake for such a long part of the day, as is usual with intermittent fasting, your body may have to get used to it. Low blood sugar can be uncomfortable, especially at first, which occurs naturally after a period of fasting. It may manifest itself, for example, with headaches or dizziness.

Over time, however, the body is able to adapt to this state and starts to use mechanisms that prevent such low blood sugar levels. Healthy adults can thus afford to experiment with this pattern. However, diabetics and people diagnosed with impaired glucose tolerance should consult their doctor, especially if they are taking medication to control their glycaemia.^[1,15]

6. May have a negative effect on mental health

Research shows that intermittent fasting can be risky for people who suffer from eating disorders such as anorexia nervosa, bulimia nervosa or binge eating. For some, it can also increase the risk of developing these problems. This adverse effect seems to be most common in adolescent girls and young women. ^[15]

7. Causes a reduced sense of thirst

Restricted dietary intake may be associated with lower fluid intake, due to a lowered sense of thirst. However, this may not reflect the actual need for fluid. Some people experience minimal thirst, but their body still needs water to function properly. Therefore, even in times of fasting, when feelings of thirst are lower, it is important to make sure that you are drinking enough. ^[1]

Our article How Insufficient Drinking Affects Your Health explains how insufficient drinking affects your health and how much fluid you should drink per day.

8. May cause digestive problems

Intermittent fasting can cause digestive discomfort, especially when you are starting out. Typically, constipation, for example, can occur. The body, including the digestive system, is still getting used to the new regime and may take a few days to adjust. In this case, it is also important to make sure that you drink enough, get enough fibre and exercise. ^[5,17]

For whom is intermittent fasting suitable?

As you have already discovered, intermittent fasting may suit some people, but it is certainly not suitable for everyone. It all depends on everyone’s individual needs and preferences. Who can benefit from it?

• Healthy people who are not comfortable with a traditional diet and prefer to eat only at certain times of the day.
• People with flexible lifestyles who can fit this specific way of eating into their daily routine.
• Individuals who want to lose weight or are looking for a way to learn to control hunger and sweet cravings.
• People who want to experience for themselves the possible positive effects on the brain, concentration, cholesterol or blood sugar levels and its other benefits.

Intermittent fasting is suitable for both men and women. However, women should be particularly careful to ensure that they are able to take in the optimum amount of calories. They are more sensitive to an insufficient intake than men. Active women who take in less energy than their bodies need over a long period of time and over train can develop the so-called female athletic triad. This combines low energy availability, menstrual dysfunction and reduced bone density.

If you want to read more about the female athletic triad, don’t miss our article How to Combat Menstrual Loss and Other Symptoms of the Female Athletic Triad? 

For whom is intermittent fasting not suitable?

Intermittent fasting is not suitable for everyone. There are certain situations in which it may pose a risk. What are they?

• During pregnancy and breastfeeding, women should rather not take up this way of eating. For example, there is a risk that fasting may adversely affect breast milk production. In addition, there are no studies that have looked at the effect of intermittent fasting during these periods of life. ^[18]
• When working shifts, it can be a problem to maintain this specific routine in the long term.
• People who suffer from eating disorders are at risk of worsening the course of their disease.
• For specific health problems, intermittent fasting could pose a risk. For example, cancer is demanding of calorie and protein intake, which a person with this type of diet would probably not be able to take in.
• Taking medication that needs to be taken with meals and at certain times of the day may also be a problem.
• This method of eating is not suitable for children either. ^[17]

Is intermittent fasting healthy?

Intermittent fasting has its health benefits, so we can say that for some people it is a healthy way of eating. However, the condition is that only those people for whom it is safe should try it. At the same time, it is important to ensure that you have the right diet composition and adapt your routine so that it is sustainable.

On the other hand, we cannot claim that this is a miracle that will solve all your problems. It cannot be considered a better way of eating than the classic rational diet typically spread out over the whole day. In fact, with it too, you can lose weight healthily, lower your blood sugar or cholesterol levels and improve your overall health. So, again, each one of you is different and you should choose a method that best suits you.

How to get started with intermittent fasting?

Have you decided that intermittent fasting is right for you and you would like to try it? Then make sure you go about it the right way. How should you proceed?

• Ideally, consult a nutritionist, i.e. a nutritional therapist or nutrition consultant. They are best equipped to advise you on how to get your diet just right.
• Choose an appropriate form of intermittent fasting. It should be consistent with your regular daily routine and lifestyle.
• Make sure you are receiving sufficient energy and nutrients.
• Follow a drinking routine. 
• Monitor your progress. You can record not only what you eat, but also your weight, the length and quality of your sleep, and your training performance.
• For example, you could try one of the apps that are designed specifically for intermittent fasting.
• Do not neglect getting sufficient sleep and physical activity.
• Observe your body. If you start to become aware of, for example, excessive fatigue or poor recovery after a workout, you may need to make a change somewhere. ^[1,14]

Which foods are allowed during intermittent fasting?

The concept of intermittent fasting does not dictate which foods are or are not appropriate. Practically, this means that no foods are forbidden. However, it is important to remember that if you want to reap the benefits that this diet offers, it is not enough just to do the fasting itself. It is also important to follow a varied and balanced diet, with plenty of all the essential nutrients.

Sample intermittent fasting diet for a woman

Let’s take a look together at what a diet might look like for a healthy adult woman who wants to maintain her weight while following the 16:8 intermittent fasting protocol. The example diet is for a 30-year-old woman with a body weight of 65 kg and a height of 170 cm, who has a sedentary job, walks roughly 10 000 steps a day and goes to the gym three times a week. Her total daily energy intake is roughly 2000 kcal and she should consume roughly 120 g of protein, 67 g of fat, 230 g of carbohydrates and 25-30 g of fibre per day.

Daily food	Time	Food	Serving
Lunch	12 midday	grilled chicken breast rice (cooked) vegetable salad	150 g 200 g 150 g
Afternoon snack	15 hours	white yoghurt oatmeal banana raspberries walnuts	150 g 40 g 110 g 40 g 30 g
Dinner	18 hours	baked trout potatoes (boiled) broccoli	120 g 150 g 100 g
Second dinner	20 hours	wholemeal toast ham cheese with 30% fat cherry tomatoes	2 pieces 2 slices 2 slices 100 g

Sample intermittent fasting diet for a man

Now let’s imagine a diet that is suitable for a healthy adult male. This man is also thirty years old, weighs 80 kg and measures 180 cm. He also walks about 10,000 steps a day, does sedentary work and strength training three times a week. His total daily energy intake is roughly 2500 kcal and his nutrient intake should consist of roughly 150 g protein, 83 g fat, 290 g carbohydrates and 25-30 g fibre.

Daily food	Time	Food	Serving
Lunch	12 midday	grilled chicken breast rice (cooked) vegetable salad	190 g 250 g 150 g
Afternoon snack	15 hours	white yoghurt oat flakes banana raspberries walnuts	150 g 40 g 110 g 40 g 30 g
Dinner	18 hours	baked trout potatoes (boiled) broccoli	150 g 200 g 100 g
Second dinner	20 hours	wholemeal toast ham cheese with 30% fat cherry tomatoes	4 pieces 4 slices 3 slices 100 g

What supplements can be taken during intermittent fasting?

Sometimes we can’t get all the nutrients we need, so we can appreciate the help of nutritional supplements. You can use these even if you are intermittently fasting. However, to do it right, you should take them within the time window allotted for food intake. Which supplements are suitable?

• Whey protein is great for supplementing protein when you can’t manage to consume it in the form of food. For vegans or those who avoid dairy, plant-based proteins are ideal.
• Gainer will be appreciated when gaining weight, but also when you need to replenish calories and carbohydrates, but food servings are too big for you. In this case, a complex blend of nutrients such as FueGain is ideal.
• Fibre comes in handy when your diet is lacking in it.
• Vitamins, minerals and omega-3 fatty acids can also help support your health.
• Supplements can also add to the aforementioned benefits of intermittent fasting. Anti-ageing action can be supported with anti-ageing supplements and brain or concentration with popular nootropics.

Is it permitted to drink while fasting?

You don’t have to avoid liquids during the window of time you are fasting. You can enjoy any non-caloric beverages such as water, unsweetened tea, coffee without milk or sugar, or beverages sweetened with artificial sweeteners. Sugar-sweetened beverages, milk, juices and others that contain calories should be consumed during the time you have set aside for eating.

What should you remember?

Intermittent fasting is a way of eating that is popular with many, especially because of its flexibility. It allows you to concentrate your meals into smaller portions throughout the day, which also proves to be beneficial for weight loss or hunger control. In doing so, it also has other health benefits, such as a positive effect on the heart or brain. If you’ve decided that this way of eating might be right for you, go about it the right way. Don’t forget a well-rounded diet with plenty of energy and nutrients.

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Sources:

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