The Types
Lab studies have shown that these three types of fasting can improve health and longevity:
Time-Restricted Feeding
This method limits calorie intake to a specific window that matches our circadian rhythm—our body clock that tells us when to sleep, wake, and eat. For example, eating only during an 8-to-12-hour period, such as from 10 a.m. to 6 p.m., aligns with this rhythm. When our body systems stay in sync, they work better. Late-night snacking disrupts this natural repair cycle. Fasting longer gives the body more time to heal, which improves health.
Intermittent Calorie Restriction
This means cutting calorie intake on certain days. Research often focuses on a two-day diet where you reduce calories by half and limit carbs. This short, intense approach acts like a therapy for the body. It also teaches us that we don’t need to eat constantly. When we do eat, we can choose wisely and maintain normal activities and exercise on reduced fuel.
Periodic Fasting That Mimics Diets
This type limits calories for three to five days, pushing the body to use stored glycogen and enter ketosis. While some fast without food, that can be risky. A safer option is a five-day diet with about 1,000 calories per day, which mimics fasting without losing nutrients. This method may be better than the two-day fast because it allows the body to cleanse and detoxify more deeply.
Health Benefits of Fasting
Fasting can be challenging and sometimes uncomfortable, but it has been shown to:
-
Boost cognitive performance
-
Protect against obesity and chronic diseases
-
Reduce inflammation
-
Improve overall fitness
-
Support weight loss
-
Lower the risk of metabolic diseases
-
Help cancer patients
For example, fasting during chemotherapy can stimulate the immune system and make cancer cells more vulnerable. Traditionally, cancer patients are told to increase calories during treatment, but this advice is now under review.
The Idea
Normally, our cells use glucose (a form of sugar from food) for energy. However, fasting deprives them of this fuel, forcing them to find other energy sources.
Short-term fasting, once seen as unhealthy, now shows great promise for weight management and disease prevention. However, it is important to fast safely and properly.
The Science
Fasting cleanses the body and forces cells to adapt. During fasting, the body starts gluconeogenesis, a process where the liver converts non-carb materials like lactate, amino acids, and fats into glucose. Because the body conserves energy, it burns calories more efficiently at rest, which lowers heart rate and blood pressure.
Later in the fast, ketosis begins. The body burns stored fat for energy, which aids weight loss and stabilizes blood sugar.
Fasting puts mild stress on the body, making cells stronger and more resilient—similar to how exercise strengthens muscles and the cardiovascular system. Like exercise, fasting requires proper rest and recovery, so short-term fasting is recommended.
