Whether after Carnival, during Ramadan, or for health reasons: fasting and consciously avoiding certain meals or foods is becoming increasingly common, especially among young people. At the top of the list of things to avoid are alcohol, sweets, and meat. Who can benefit from fasting to improve metabolic health, and what should people with diabetes keep in mind? Here’s an overview of the latest findings.
Is fasting healthy? – Short answer
Fasting can have health benefits under certain conditions, particularly when it results in a calorie deficit. However, the evidence from studies is mixed: while some effects, such as weight loss, are well documented, there is a lack of clear evidence for long-term improvements in metabolic health for many fasting methods. For people with Diabetes Fasting is possible, but should always be supervised by a doctor.
What types of fasting are there—and how do they differ?
There are various ways to fast. Intermittent fasting is particularly common. This involves deliberately taking breaks between meals. The most popular methods are 16:8—fasting for 16 hours and eating for 8 hours—and 5:2—eating normally for 5 days and reducing calorie intake to about 500 to 600 kilocalories for 2 days. The goal is to boost metabolism and lose weight.
The Buchinger therapeutic fast is also widely practiced; in addition to calorie-free beverages such as water and tea, it allows only vegetable broth and small amounts of protein. A scientific study on the effects of the Buchinger therapeutic fast confirms that fasting alters metabolism and mobilizes energy stored in adipose tissue. This can lead to weight loss, a reduction in waist circumference, and lower cholesterol and triglyceride levels.[1]
One of the best-known and increasingly studied methods is water fasting—a complete abstinence from solid food for several days, during which one consumes mainly water (supplemented with electrolytes if necessary). Prof. Dr. Peter Schwarz, a diabetologist and one of Germany’s leading experts in preventive medicine, describes in his book on water fasting the effects that prolonged periods of fasting can have on metabolic processes and inflammatory responses in the body.[7]
It is important to note that the body of research on fasting is still insufficient or only partially comparable. It has therefore not been fully scientifically proven that certain fasting methods, such as intermittent fasting, are superior to others and lead to a better quality of life. Nevertheless, it is generally recommended that people who are overweight or obese lose weight to reduce health risks.[2]
Water fasting as a radical approach: The perspective of Prof. Dr. Peter Schwarz
takes a much more radical stance Prof. Dr. Peter Schwarz, a diabetes specialist and head of prevention at Dresden University Hospital. While many approaches focus on moderate calorie restriction or time-restricted eating, he is specifically investigating the effects of a complete, multi-day water fast.
It is worth noting that Schwarz was initially skeptical of the topic himself. In his book, he describes how fasting was long considered a fringe practice in medicine—and that it was only through his own observations and studies that he came to explore it more deeply. Among other things, imaging tests that showed how drastically liver fat can change within a short period of time served as a catalyst.
His approach is based on a clear hypothesis: Many metabolic diseases—in particular Type 2 diabetes – are closely linked to fat deposits in organs such as the liver. While traditional diets often take time to produce results in this area, Schwarz sees water fasting as a much faster way to influence metabolism.
He describes fasting not as an exceptional state, but as part of our evolutionary heritage: the human body is designed to alternate between periods of food intake and periods of deprivation. During longer periods of fasting, the body increasingly draws on stored energy, and metabolic processes undergo fundamental changes.
At the same time, Schwarz himself points out that fasting is not a “miracle cure.” What matters, he says, is gaining a better understanding of the underlying mechanisms and applying the method in a targeted and controlled manner. His book “Water Fasting: Overcome Diabetes and Other Inflammatory Diseases in Just 14 Days” (Original title) offers insight into this way of thinking and is aimed at people who want to explore the biochemical changes that occur during prolonged periods of fasting in greater depth.
Important: The effects described by Schwarz are based in part on clinical observations and new research approaches that are currently being further investigated.
Note: Longer periods of fasting, especially water fasting lasting several days, should only be undertaken under medical supervision in cases of diabetes.
These different approaches show that fasting is viewed very differently in research—ranging from moderate dietary approaches to more radical interventions. It is therefore important to take a nuanced view of its benefits and limitations.
How healthy is fasting?
The effects of fasting remain scientifically controversial. A new study by the German Institute of Human Nutrition (DIfE) and Charité shows that while time-restricted eating shifts the body’s internal clock when calorie intake remains constant, it does not lead to measurable improvements in metabolic or cardiovascular parameters.[3] Specifically, the study examined a form of intermittent fasting in which the daily eating window lasts a maximum of ten hours and the fasting window lasts at least 14 hours.
According to the study, an eight-hour eating window can Insulin sensitivity, do not clinically significantly alter blood sugar, blood lipids, inflammatory markers, or other cardiometabolic parameters. Therefore, the key to losing weight or improving metabolism is not a shorter eating window, but rather the energy balance—that is, the actual reduction in calorie intake.
This means that if you eat just as much as usual during your eating window while intermittent fasting, you won’t see any measurable metabolic benefits. The effect isn’t caused by skipping meals per se, but by the resulting calorie deficit.
How healthy is fasting for people with diabetes?
Even people with diabetes—whose condition is well-managed—can fast and benefit from it. Specifically, people with Type 2 diabetes lose weight under certain conditions because they consume fewer calories overall during the fasting phase. Another positive effect: During fasting, less or no glucose is absorbed from food, which can lower insulin levels or the body’s need for insulin. The cells then become more sensitive to the body’s own Insulin – so-called insulin sensitivity may improve.
However, everyday life shows that many people tend to reach for sweet snacks when they start to feel hungry or experience slight fluctuations in blood sugar during long breaks between meals or while intermittent fasting. The resulting craving for sweets can trigger additional appetite and undermine the actual goal—to eat more mindfully and in a more controlled manner.
An alternative could be neutral-tasting carbohydrate sources that are used specifically and without a pronounced sweet taste. Products such as Hyporest® This is exactly where they come in: They provide readily available carbohydrates in specific amounts without the typical “craving effect” that often leads to uncontrolled overeating. Especially during longer breaks between meals or structured fasting periods, this can be a practical way to consume carbohydrates without triggering additional hunger pangs.
In addition, fasting can trigger a process known as autophagy, a form of cellular recycling in which damaged or unnecessary cellular components are broken down and recycled. This process is currently the subject of intensive research and is associated with positive long-term effects on metabolism and inflammatory processes.[4] However, the extent to which this effect is clinically relevant in humans has not yet been conclusively determined.
For people with type 2 diabetes who want to lose weight, fasting can therefore be a useful tool—provided that blood sugar levels and medication are closely monitored and adjusted. In a large British study, significant weight loss even led to remission of type 2 diabetes.[6]
What are the risks of fasting when you have diabetes?
Those affected should be especially careful when fasting. With Type 1 diabetes You should only fast if your blood sugar is closely monitored and you have consulted with your healthcare team. The risk of hypoglycemia (Hypoglycemia) is elevated; at the same time, hyperglycemia and, in extreme cases, ketoacidosis can occur—especially if insulin doses are not adjusted properly. It is important to note that basal insulin should not be discontinued on one’s own initiative, even during fasting.
Although modern technologies such as Insulin pumps and continuous glucose monitoring systems (CGM) Fasting is safer—these systems allow for continuous monitoring of blood sugar levels and enable early intervention. Nevertheless, fasting is not a standard approach for people with type 1 diabetes, but rather an individual decision made under medical supervision. For example, it should be determined in advance at what blood sugar levels or symptoms fasting should be stopped immediately.
Fasting is generally possible for people with type 2 diabetes, but their treatment may need to be adjusted to accommodate changes in mealtimes. Here, too, it is essential to discuss dosages and timing with a doctor or endocrinologist. For example, taking blood sugar-lowering medications on an empty stomach can be problematic. At the same time, you should not stop taking medications that help stabilize blood sugar on your own. Some medications must be taken at specific times of day or with a meal—incorrect administration can either enhance or reduce their effect or lead to side effects.[5]
Tremors, dizziness, extreme fatigue, or frequent urination should be taken seriously: they may indicate low blood sugar or very high blood sugar levels. This is the body’s way of signaling that fasting is not agreeing with it. In this case, you should stop fasting immediately and consume fast-acting carbohydrates—for example, glucose – be supplied.
Women with [condition] should not fast at all Gestational diabetes and people with diabetes who frequently experience hypoglycemia. Fasting is also not recommended for people with poorly controlled diabetes.
Diabetes and Fasting at a Glance
| Topic | Assessment |
|---|---|
| Intermittent fasting (16:8 / 5:2) | Possible if diabetes is well-controlled; consultation with a doctor is recommended |
| Therapeutic fasting according to Buchinger | Only under medical supervision; evidence of weight loss is available |
| Water fasting | Only under strict medical supervision; limited research data available |
| Type 1 diabetes | High risk of hypoglycemia; CGM and medical supervision are mandatory |
| Type 2 diabetes | In principle, this is possible; medication must be adjusted |
| Gestational diabetes | Fasting is not recommended |
| Key to weight loss | Calorie restriction – it’s not just about the time window |
Frequently Asked Questions About Diabetes and Fasting
Can fasting improve or cure diabetes?
Fasting can improve insulin sensitivity and lower blood sugar levels over the long term in people with type 2 diabetes. In some cases, remission has been reported following significant weight loss.[6] However, fasting alone is not a cure in the medical sense—any changes to treatment must always be supervised by a doctor.
What happens to blood sugar levels during fasting?
During fasting, the body absorbs less or no glucose from food. Insulin levels drop, and the cells’ sensitivity to insulin may increase. However, in people with diabetes—especially those on insulin therapy—blood sugar levels can drop sharply and trigger hypoglycemia.
Is intermittent fasting beneficial for people with type 2 diabetes?
Yes, under medical supervision and with appropriate medication. However, the effect only occurs with an actual reduction in calorie intake—not simply because of the shorter eating window.
What should you do if you experience hypoglycemia while fasting?
Stop fasting immediately and consume fast-acting carbohydrates—such as glucose (Glucose). Check your blood sugar again after 15 minutes. If it hasn't returned to normal, consume more carbohydrates and seek medical help.
How long can you fast if you have diabetes?
This depends on the type of diabetes, medication, and individual blood sugar levels. The shorter the fasting window, the lower the risk. In general, longer fasting periods should only be undertaken under medical supervision if you have diabetes.
Sources
- Wilhelmi de Toledo F, Grundler F, Bergouignan A, Drinda S, Michalsen A. Safety, health improvement, and well-being during a 4- to 21-day fasting period in an observational study involving 1,422 participants. PLoS One. 2019;14(1):e0209353. https://aerztegesellschaft-heilfasten.de
- German Society for the Study of Obesity. S3 Guideline on Obesity – Prevention and Treatment [Internet]. AWMF; 2014 (updated 2023) [accessed Jan. 2024]. Available at: https://www.awmf.org/leitlinien/detail/ll/050-001.html
- German Center for Diabetes Research. Intermittent fasting without calorie restriction does not improve metabolic health, but it does shift the body’s internal clock [Internet]. DZD; 2024 [accessed Jan. 2024]. Available at: https://www.dzd-ev.de
- Levine B, Kroemer G. Autophagy in the pathogenesis of disease. Cell. 2008;132(1):27–42. https://doi.org/10.1038/nrm2696
- German Diabetes Society. Clinical Practice Guidelines of the German Diabetes Society [Internet]. Berlin: DDG; 2023 [accessed Jan. 2024]. Available at: https://www.ddg.info/leitlinien-empfehlungen/leitlinien
- Lean MEJ, Leslie WS, Barnes AC, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomized trial. Lancet. 2018;391(10120):541–551. https://doi.org/10.1016/S0140-6736(17)33102-1
- Schwarz, P. Water Fasting: Overcoming Diabetes and Other Inflammatory Diseases in Just 14 Days – The Latest Medical Findings. 1st ed. 2022. ISBN 978-3-7558-0080-4.
Medical Note: This article is intended solely for general informational purposes and is not a substitute for individual medical advice. People with diabetes should always consult a qualified healthcare professional (diabetologist, primary care physician) before making any changes to their diet, fasting methods, or medication. If you experience symptoms of hypoglycemia, take immediate action and seek medical help if in doubt.
