In recent years, intermittent fasting has slowly become a mainstream diet . Many people rely on longer meal intervals to control their weight. Many are surprised to find it much more sustainable and less restrictive than traditional diets like keto, calorie counting, and many others.
Because of the benefits of intermittent eating, which improve overall health, reduce the risk of disease, and increase metabolic health , intermittent eating is also of interest to those who are not necessarily seeking to lose weight.
In addition to weight loss, there are other surprising health benefits, such as lowering insulin and blood sugar levels.
In this article we will take a closer look at:
- whether intermittent fasting actually works.
- what effects intermittent fasting can have on our body.
- how to do intermittent fasting correctly and safely.
- how to measure success.
The basic idea of intermittent fasting
What exactly is intermittent fasting?
Regardless of the specific approach, intermittent fasting involves restricting the time window during which you eat. The most popular approaches are 16:8, 20:4, and 5:2. The numbers refer to the hours between fasting and eating in a day (16:8 and 20:4) or the days between eating and fasting in a week (5:2).
Where does intermittent fasting come from?
The practice of intermittent fasting was inspired by prehistoric times seeking solutions to a modern problem. Thousands of years ago, food wasn't available in the abundance many of us are accustomed to today. Therefore, the human body adapted to be able to continue functioning during the hours, days, or even weeks it took our ancestors to find food.
When we don't eat, our blood sugar levels drop, which can be problematic because our brain relies on blood sugar as fuel to function. However, the human body has developed defense mechanisms that prevent this from affecting our cognitive and metabolic functions, allowing us to continue searching for (and eventually finding) food to survive.
Fasting activates alternative energy sources stored in the body, such as fat, and triggers the production of ketone bodies to fuel the brain. In overweight people, fasting promotes a reduction in insulin levels (a hormone that helps transport glucose from the blood into the cells), ultimately leading to weight loss. During fasting, the body is also more sensitive to certain hormones, meaning the body is more responsive and better able to absorb nutrients from food when the fast is finally broken.
When do you start fasting?
The good news is that, whether you realize it or not, you're probably already reaping some of these benefits by practicing intermittent fasting during sleep! Eating your last meal a few hours before bed and your morning meal an hour or two after waking up will result in a fasting period of 12-13 hours.
However, intermittent fasting, as discussed in this article, is about more than just abstaining from late-night snacks. Intermittent fasting refers to the additional observance of fasting periods during which overweight people or those with type 2 diabetes abstain from food during the day to lower insulin and blood sugar levels and support weight loss. Here's how it works.
How exactly does intermittent fasting work?
When should you eat and when not?
The most common intermittent fasting model is 16:8. This means you go 16 hours without eating anything, while maintaining an 8-hour window in which you consume all the food and (calorific) drinks you would normally eat throughout the day.
Many people interpret this to mean they can indulge in any high-calorie snacks they want. Or they believe that the 16:8 diet means they should simply skip breakfast. Prof. Dr. Herzig, Director and Scientific Director of the Helmholtz Diabetes Center, however, points to studies that show that skipping breakfast is not the best way to practice intermittent fasting, but still leads to results:
"Eating early in the morning, having lunch, and then having the last meal in the late afternoon is better in terms of health parameters than skipping breakfast. However, everyone can ask themselves what they would prefer and whether it is easier for them in everyday life to skip breakfast or dinner." (Dr. Stefan Herzig)
For most people, replacing dinner with a late-afternoon meal is more difficult than skipping breakfast, because dinner is a social event shared with friends and family. It might be awkward if someone invites you over for dinner and you sit there with just a glass of water, politely refusing to try any of the food. Prof. Dr. Herzig says that while it's not optimal to practice intermittent fasting if you start the 8-hour eating window later in the day, thus skipping breakfast, it's " still beneficial ."
How much should I eat during intermittent fasting?
However, intermittent fasting isn't about skipping meals or reducing calorie intake. The idea is that you still consume the same number of high-quality calories your body needs each day, but in a smaller, set time window, rather than binge-eating and snacking throughout the day.
What should you eat during intermittent fasting? What should you pay attention to?
There is no standard protocol for intermittent fasting, to promote health and longevity. But many plans limit total calorie intake, making food quality the top priority.
We recommend planning the most nutritious meals and snacks. This means mixing up processed foods and focusing on fresh, healthy, and colorful foods. Yes, you can eat cake, but it's much better as a snack after a meal rich in fiber, protein, and fat, rather than on an empty stomach when breaking your fast. You'll notice this in your blood sugar levels and feel better overall.
The first meal of the day counts
It depends on how you break your fast.
A high-carbohydrate breakfast can put you on a glucose roller coaster for the rest of the day. It really sets the tone. If your first meal contains fat and protein (before the carbs), your blood sugar will be more stable than if you start with a high-sugar meal that causes a glucose spike. Here are some recipes for blood sugar-friendly breakfast ideas .
How long does the effect of intermittent fasting last?
When you stop intermittent fasting, your body returns to its original state almost immediately. This means that the benefits of intermittent fasting only become apparent when you actively practice it. However, if you stop and start intermittent fasting again, the benefits return very quickly.
This means it's very easy to take a break from intermittent fasting, such as a weekend or a week, and then get back into it. As Prof. Dr. Herzig explains, "It's a very responsive thing that happens, and therefore the longer and the more consistently you do it, the better."
Is intermittent fasting suitable for everyone?
In addition to weight loss, intermittent fasting has been shown to be effective in reducing insulin resistance in people who are overweight or have type 2 diabetes. However, if you're already at a healthy weight and don't have type 2 diabetes, some studies have shown that intermittent fasting can actually lead to unhealthy metabolic consequences.
Although healthy participants in one study lost weight, intermittent fasting also led to increased insulin resistance, fasting glucose, and lipids.
There is therefore limited evidence that intermittent fasting is more effective than a healthy, nutritionally balanced, and calorie-controlled diet for healthy people within their desired weight range.
Should women do intermittent fasting?
As mentioned above, intermittent fasting has become very popular, especially skipping breakfast and eating two more substantial meals. However, intermittent fasting is not the best diet for every woman.
When should women not do intermittent fasting?
First, for women with hormonal imbalances, especially PCOS, a good breakfast is very important for lowering insulin and testosterone and improving ovulation. This is important not only for fertility but also for long-term health.
Second, intermittent fasting can trigger eating disorders, as women may be prone to overeating during the eating window. This deserves special attention, as studies have shown that up to 23 percent of women with PCOS are prone to eating disorders.
Intermittent fasting can also place additional stress on the body during menopause. Many women practice intermittent fasting to lose weight during menopause . However, while the body is subject to significant hormonal fluctuations, intermittent fasting may not provide optimal support.
Intermittent fasting is also probably not a good idea for pregnant and breastfeeding women. The natural calorie restriction created by intermittent fasting can negatively impact fetal development. Since the mother's diet largely depends on what she eats, a restricted diet during breastfeeding can lead to less nutritious milk and thus affect the development of the newborn.
What might this look like in real life?
Along with a hearty and filling breakfast, a gap of at least 12 hours between dinner and breakfast the next morning can improve insulin sensitivity.
A 12-hour gap shouldn't be too difficult to achieve. For example, a woman could choose to fast between 7 p.m. and 7 a.m. She would then have to finish dinner before 7 p.m. and wait until 7 a.m. to have breakfast, but would sleep most of the time in between.
The benefits of intermittent fasting
Lower insulin & weight loss
Aside from the (optional) limited calorie intake, the idea is that when you don't eat, your insulin levels drop, allowing your fat cells to release their stored sugar for energy and keep your blood sugar levels steady. You could say your body flips a metabolic switch.
This increases insulin sensitivity and allows your body to respond better to insulin secretion. Less insulin is needed to transport the glucose in your blood to the cells, where it is used as energy.
Lowering insulin will help you lose weight. Too much insulin can inhibit fat burning and thus make weight loss more difficult.
When you eat constantly, your body doesn't need to access energy stores in the form of fat because it has energy available in the form of glucose—its preferred fuel. Learn more about this in our blog post on weight control and blood sugar .
Reduce inflammation
Eating less frequently can also help reduce inflammation , which is good because it also reduces insulin resistance. Here's why:
When you eat constantly, especially on a high-carbohydrate diet, your body constantly releases insulin, triggered by glucose intake. Over time, insulin builds up in the body, and cells can no longer use it as effectively as before—a phenomenon known as insulin resistance. The cells become "numb" in their use of insulin, which is important for storing glucose. This, in turn, leads to higher blood sugar levels and inflammation.
So, if you limit your calorie intake to a smaller time window AND eat healthier, you can reduce your risk of diseases such as cancer , diabetes, cardiovascular disease, and Alzheimer's.
Strengthens our circadian rhythm
Another notable benefit of intermittent fasting is that it boosts our natural circadian rhythm. Deep within every person's brain, there's a master clock that stimulates our body to engage in certain activities based on external cues like sunlight.
This so-called circadian rhythm is comparable to a smartphone with a whole day's worth of preset alarms—wake up, eat lunch, etc.—only much less annoying. Our circadian rhythm also includes a glucose/insulin timer. Sensitivity to insulin decreases throughout the day.
Our bodies take longer to process a piece of bread at 9 p.m. than at lunchtime. So eating dinner earlier in the day (for example, by following a 16:8 schedule and only eating between 10 a.m. and 6 p.m.) increases the circadian effectiveness of insulin.
This circadian rhythm also explains why blood sugar levels rise and fall during sleep , even when you don't eat. Besides the circadian rhythm, there are other factors that influence our blood sugar at night :
- Dreams and REM sleep : Non-REM sleep is associated with a rise in blood sugar levels, while REM sleep is associated with stable blood sugar levels. Therefore, blood sugar levels can depend on the sleep phase.
- Meals eaten during the day : High-carb meals lead to higher fluctuations throughout the day. That's why at Hello Inside, we believe food quality and meal order are crucial to avoiding the blood sugar roller coaster that continues into the night.
Long-term effects
Intermittent fasting can be a viable, consistent way to increase insulin sensitivity and lower average blood sugar levels. By shifting our eating window earlier in the day, we align our food intake with the time when our body is naturally most sensitive to insulin, thus lowering peak insulin and blood sugar levels.
Your blood sugar levels can have a significant impact on how your body feels and functions. Therefore, stable blood sugar levels can be an important factor in your overall well-being and guide your own eating habits. So let's take a final look at some ways you can make IF work for you.
Accompanying intermittent fasting with a continuous glucose monitor (CGM)
If you want to start intermittent fasting, monitoring your blood sugar levels is especially important. This way, you can ensure that intermittent fasting is working and monitor your metabolism . It's also important to pay attention to whether your blood sugar levels drop too much. If this is the case, you should modify your intermittent fasting to stabilize them. High blood sugar levels aren't the only immediate negative side effects. If your blood sugar levels are too low, it can lead to short-term symptoms such as dizziness, cravings, fatigue, and difficulty concentrating. As always, if in doubt, it's best to consult a doctor.
In the long term, intermittent fasting can not only support your metabolism but even help you lose weight, as described above.
Firstly, because you may consume fewer calories in the shorter time window. And secondly, because you ideally stabilize your blood sugar, thus improving your insulin sensitivity and thus reducing cravings, for example.
5 tips to get started with intermittent fasting for better blood sugar balance
If you haven't tried intermittent fasting yet:
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Plan healthy, nutritious meals in advance
While you may be tempted to indulge in your favorite snacks and delicious meals once your fast is over, you should stick to a healthy diet rich in protein, fruits, and vegetables.
Choose a hearty meal to break your fast (e.g., eggs, tofu, avocado, cheese). Make sure your meals are colorful and high in fiber so you get all the nutrients you need and stay full longer. Eat sugar and refined grains last or for dessert. Here's a blood sugar-friendly shopping list . -
Drink enough
Make sure you stay well hydrated, especially during fasting periods. This includes water, herbal teas, and calorie-free flavored drinks. -
Move
Let your body burn fat between meals. Don't snack. Stay active throughout the day. Build muscle. Exercise and movement are important for a healthy metabolism and blood sugar balance. -
Start with a modified schedule
Start with a schedule that's realistic for you and your routine, and then gradually increase the intensity and duration. You don't have to dive headfirst into the program right away. Consider a simple form of intermittent fasting that works for you. Test out which fasting phases are easiest for you to maintain and which make you feel best. -
Listen to your body
Keep track of how your body responds to your diet changes by monitoring your blood sugar levels with a continuous glucose monitor (CGM). Hello Inside lets you track your blood sugar levels over time with a CGM so you can see if your lifestyle supports a healthy life.
Keep in mind that intermittent fasting may not be the right solution for you if you are already within a healthy weight range or do not have type 2 diabetes.
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