Intermittent Fasting

A new diet trend has been making waves in the media for some time: intermittent fasting. We have researched what it means, how it works, and what it can do for blood pressure.

16:8 - 16 hours of fasting per day

Intermittent fasting refers to a dietary approach where no food is consumed for a certain period. This can be done daily in the 16:8 variant, where fasting occurs for 16 hours and eating is allowed during the remaining eight hours. Another variant is 5:2, where normal eating occurs for five days a week and fasting, meaning nothing or almost nothing (maximum 500 kcal), occurs for two days. A stricter variant is Alternate Day Fasting, where fasting occurs every other day.

Each of the mentioned forms has the significant advantage that this dietary approach is easier for most people to maintain than conventional diets. In the 16:8 method, it is relatively simple to extend the fasting period to 16 hours by skipping breakfast or dinner. Most people sleep at night and do not consume food during that time. One variant could be to eat until 7:00 PM, skip breakfast the next day, and then eat again from 11:00 AM. Or to have breakfast at 6:00 AM, eat lunch, and then fast from 2:00 PM until the next day at 6:00 AM.

During this limited time, if one eats normally and not more than usual, fewer calories are naturally consumed. This makes it relatively easy to achieve a calorie deficit that leads to weight loss.

In addition to the expected weight loss, intermittent fasting is also said to have a generally positive effect on the body. The long fasting period stimulates autophagy (the body's own "maintenance program"). This removes damaged or dead cells, while other cells are "cleaned" and renewed. It is essentially the cell's own cleaning and tidying crew. Autophagy also supports the immune system by eliminating pathogens that have entered the cell.

This cell-cleaning program requires certain conditions in the body to function. Glycogen stores must be empty, and no additional carbohydrates should be available for the energy supply of the cells. This is achieved, among other things, through the fasting periods of intermittent fasting. Physical activity also helps to deplete the stores. However, prolonged fasting over days or weeks has the opposite effect: it paralyzes the work of the cells, as they lack the necessary energy for cleaning and renewing.

Insulin also plays a role in autophagy. If small meals are consumed regularly throughout the day, the insulin level remains relatively stable. However, insulin inhibits autophagy. This means that during times when the insulin level is kept at a consistently high level, the cell-cleaning program cannot function. To initiate autophagy, the insulin level must drop, which happens when no further food is provided.

Many of the positive effects of intermittent fasting have only been demonstrated in animal studies so far. There are currently no reliable data on how these results can be transferred to humans.

In addition to the positive influence on blood pressure due to weight loss, a mini-study with eight overweight men diagnosed with prediabetes also showed a reduction in blood pressure values independent of weight loss. However, the study is not truly representative due to the small number of participants and their health status. It is worth mentioning that the participants, despite not losing weight as expected due to the consistent calorie intake during the shortened time frame, still experienced a decrease in blood pressure. After five weeks of intermittent fasting, their systolic blood pressure values had decreased by an average of 11 mmHg, and diastolic values decreased by an average of 10 mmHg. Insulin metabolism also improved, with a reduced insulin secretion observed after the observation period, which in turn benefited blood pressure.

Whether intermittent fasting is truly superior to other dietary or diet forms is a matter of debate. There are still hardly any long-term research results available. A study from 2017 compared 100 metabolically healthy overweight individuals. They were divided into three groups. One fasted according to the conventional method of calorie restriction (75 percent of daily energy needs), the second group observed fasting days according to alternate day fasting (25 percent of daily energy needs on fasting days and 125 percent on eating days), and the third group continued their usual diet. After a one-year observation period, no significant advantages were observed for either of the fasting groups. Both lost approximately the same amount of weight.

Intermittent fasting is therefore a method that is relatively easy for most people to implement in order to save calories overall and thus lose weight. There is no need to count calories, nor is a complete abstinence from certain foods necessary. This makes it easier for many to maintain the fasting period. However, a clear advantage over daily calorie restriction has not yet been demonstrated.

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By Sabine Croci. This article is medically reviewed. Last updated (03/2024).
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Intermittent Fasting

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