By Entela Celiku, PhD in Natural Products Chemistry & Food Chemistry Graduate
Intermittent fasting has become a buzzword among wellness enthusiasts, biohackers, and even doctors. From detox teas to time-restricted meals, fasting is being presented as a miracle strategy for weight loss, longevity, and metabolic health. But behind the glossy headlines, what does science actually say about fasting? And more importantly, is it safe for everyone?
Fasting isn’t something new. People have done it throughout history, sometimes because there wasn’t enough food, other times as a spiritual practice. Today, it’s being promoted as a health trend. But is it right for everyone? What does science say? And what have I learned through my own life and work?
What Is Intermittent Fasting?
Fasting means taking regular breaks from eating. Intermittent fasting (IF) isn’t one strict rule, but rather a pattern of eating. Some people fast daily by limiting food intake to a set time window, such as eating only between noon and 8 PM. Others follow the 5:2 method, eating very little (around 500 calories) on two non-consecutive days each week. There’s also alternate day fasting, 24-hour fasts once or twice a week, or longer fasts supervised by medical professionals.
Another more flexible approach is intuitive fasting, listening to your body and skipping a meal when you simply aren’t hungry. This could be after a heavy dinner, for example. Contrary to popular belief, it’s not harmful to skip a meal now and then. In some cases, it’s better than forcing yourself to eat something processed or nutritionally poor.
What Happens in Your Body When You Fast?
When you fast, your body first uses up stored sugar (called glycogen). After 12 to 24 hours without food, it begins burning fat to produce ketones, an alternative fuel that powers your brain and muscles. This switch to fat-burning is called ketogenesis, and many people report feeling more alert and energized once it kicks in. This process can also bring about physical side effects. Some people feel tired, irritable, or even nauseous as their bodies adapt. To support your system, staying well hydrated, about 2 to 2.5 liters of water per day, is essential. Your body releases more waste during fasting, and water helps flush it out. Fasting also supports pathways related to cellular repair and longevity, similar to how NAD+ works in the body. Learn more about NAD+ and how it fuels your cells here.
Another powerful effect of fasting is the activation of autophagy. This is your body’s natural cleaning system that breaks down and recycles damaged cells. It’s a key reason why fasting is being explored for its potential to reduce the risk of age-related diseases such as Alzheimer’s and Parkinson’s.
The Benefits of Fasting (According to Science)
Scientific studies suggest fasting may help regulate insulin, reduce inflammation, and support weight loss, especially in people who are overweight. Some studies have shown improvements in cholesterol and triglyceride levels. In animal research, fasting has been linked to longer lifespans and reduced cancer risks. However, these results are not always mirrored in human studies. Benefits depend on many factors, including what kind of fasting you do, your body type, lifestyle, and underlying health conditions.
Fasting and Cancer, A Critical Perspective
In recent years, some research have claimed that fasting can “starve” cancer cells. While the idea may sound compelling, it’s far from simple. Cancer is already a state of low energy. The body is working hard and often struggling to access or produce energy properly. Fasting can add more stress, pushing the body to use up muscle and organ tissue for fuel, and increasing levels of stress hormones like cortisol.
Meanwhile, cancer cells are incredibly adaptive. When glucose is low, they don’t just die, they shift to using fats or amino acids. In practice, I’ve seen people with cancer lose precious strength trying to restrict their food. Rather than starving the body, we should be nourishing it. Healing requires energy: for the immune system, for rebuilding tissues, for thinking clearly and staying active. Recovery is about restoration, not deprivation.
Is Fasting for Everyone?
One important consideration, especially for women, is how fasting can affect hormonal health. In some cases, prolonged or restrictive fasting may lead to menstrual irregularities or even loss of the menstrual cycle altogether. This is because the female body is highly responsive to changes in energy availability. When calorie intake drops too low or fasting windows are too long, the body may interpret this as a state of stress and reduce the production of reproductive hormones. This can result in amenorrhea (the absence of menstruation), which is a clear sign that the body is not receiving enough support to maintain normal functions. Some common signs that your body may not be tolerating fasting well include loss or irregularity of menstrual cycles, persistent fatigue, feeling cold or sluggish, reduced libido, changes in mood, and in long-term cases lower bone density. These are important signals that your body needs more energy and support. If you experience any disruptions in your menstrual cycle during fasting, it’s essential to reassess your approach and prioritize nourishment and hormonal balance.
Fasting isn’t suitable for everyone. Children, teens, and women who are pregnant or breastfeeding need regular nourishment for growth and development. People with type 1 diabetes, eating disorders, or chronic illnesses should also avoid fasting unless under medical guidance. Even in healthy individuals, starting a fast can come with side effects like fatigue or mood swings. It’s important to start slowly, pay attention to how your body reacts, and never ignore symptoms.

What Does the Research Actually Show?
So far, most clinical studies on fasting in humans are short-term. In 13 trials lasting from two weeks to six months, the majority showed modest weight loss ranging from one to eight percent of body weight. Some participants had better insulin control or lower markers of inflammation. However, results varied based on the method used and who was participating. Many people found strict fasting methods difficult to maintain, especially alternate-day fasting.
The Role of Circadian Rhythms and Meal Timing
Emerging science suggests that when we eat may be just as important as what we eat. Animal studies show that eating in line with the body’s natural circadian rhythm, during daylight hours, helps prevent weight gain and metabolic issues. In humans, this might mean avoiding late-night snacking and keeping meals within a set daytime window. Aligning with our internal clock seems to support better sleep, energy, digestion, and long-term health.
My Personal Philosophy on Fasting
I’ve always been guided by the words of Hippocrates, the father of modern medicine: “Let food be thy medicine.” For me, health comes from balanced, consistent nourishment. I eat three complete meals every day, filled with plants, healthy fats, and clean proteins. My dinner is always at 6:30 PM. This simple habit naturally gives my body a 13- to 14-hour overnight fasting period. It’s not extreme. It’s sustainable. And it’s something I recommend to many people who want to support their health without going to extremes.
Gentle, Safe Fasting: How to Begin
If you’re curious about trying fasting, the safest place to start is by moving your dinner a little earlier and delaying your breakfast by an hour or two. Focus on eating real, nourishing foods, plenty of vegetables, whole grains, protein from fish or legumes, and good fats like olive oil, nuts and butter. Make sure to drink water throughout the day, and avoid skipping meals if it makes you feel light-headed or weak.
Always consult a doctor before beginning any new diet, especially if you have a medical condition or take medication.
The Kungul Approach to Wellness
At Kungul, we believe knowledge is the key to health. Whether you’re choosing a toothpaste, a face cream, or a new supplement, understanding the ingredients and how they affect your body is the first step. Download the Kungul app to scan your products, learn about hidden ingredients, and receive health-conscious recommendations. We’re here to support you in making informed, balanced choices without fear, and without extremes.
Stay curious. Stay nourished. And always, listen to your body.