Fasting involves abstaining from caloric intake to shift the body into a metabolic state that relies on stored energy. The primary goal is to keep the hormone insulin low and stable, signaling the body to burn fat and initiate cellular cleanup processes. Since drinking is permitted, the focus must be on liquids that do not trigger a digestive response or increase insulin levels. The acceptability of any beverage hinges entirely on its caloric and macronutrient content.
Essential Zero-Calorie Options
The most straightforward and universally accepted liquids during a fast are those with zero or near-zero calories, ensuring no metabolic disruption occurs. Plain water, in both still and sparkling forms, is the foundation of any fasting regimen and is entirely safe. Proper hydration supports physiological functions and helps manage hunger pangs.
Black coffee is another reliable option, provided it is consumed without additions like sugar, cream, or milk. Coffee contains compounds that may support the fasting state, with some research suggesting regular consumption is associated with reduced fasting insulin levels. The negligible caloric content ensures it will not activate the digestive system.
Similarly, plain, unsweetened tea—whether herbal, green, or black—is safe to drink. These calorie-free beverages contain beneficial antioxidants and phytochemicals that do not interfere with metabolic goals. Adding any form of sugar, honey, or milk will compromise the fasted state. Ensure that herbal tea does not contain dried fruit pieces or added flavorings that might contribute unexpected sugars.
Navigating Low-Calorie Additives and Broths
This category consists of liquids and additions that introduce a minimal caloric load, creating a gray area regarding the definition of “breaking a fast.” Bone and vegetable broths are frequently utilized, especially during longer fasts, because they offer a supply of electrolytes and minerals. A typical cup of bone broth contains a small amount of calories, often between 40 and 50, primarily from protein and fat.
While these calories technically break a strict, zero-calorie fast, the minimal caloric and protein content often does not significantly disrupt fat-burning. Broth is helpful for improving compliance and reducing lightheadedness, as the sodium content helps maintain electrolyte balance. However, for those fasting specifically for cellular renewal (autophagy), the presence of protein and calories may be enough to signal the growth pathway mTOR and interrupt the process.
Non-caloric artificial sweeteners present ambiguity because their impact is less about calories and more about the potential for an insulin response. Sweeteners like sucralose, aspartame, and stevia contain zero or very few calories. However, the sweet taste can still cause a debated cephalic phase insulin release in some individuals. Furthermore, some zero-calorie sweeteners may affect the gut microbiome, potentially impacting glucose metabolism over time.
Because of this uncertainty, it is generally recommended to avoid artificial sweeteners entirely or use them sparingly for compliance. Small additions are typically acceptable, such as a squeeze of fresh lemon or lime juice, a dash of cinnamon, or a teaspoon of apple cider vinegar mixed into water. These additions are unlikely to cause a measurable insulin spike because the volume of fruit juice adds negligible sugar, and apple cider vinegar is calorie-free.
Beverages That Will Break Your Fast
Any drink containing a significant number of calories, especially from carbohydrates, will definitively break a fast by triggering the body’s digestive response. Carbohydrate consumption, such as sugar, causes a rapid rise in blood sugar, prompting the pancreas to release a surge of insulin. This rise in insulin abruptly ends the fasted state and shifts the body out of fat-burning mode.
This category includes all regular sodas, sports drinks, and fruit juices, even fresh-pressed varieties, due to their high sugar content. Beverages containing protein or fat will also interrupt a fast because these macronutrients stimulate digestion and activate growth pathways. Therefore, avoid milk (dairy or plant-based alternatives like oat or soy) and any coffee or tea containing creamers, sugar, or syrups. Alcohol also breaks a fast because the body prioritizes metabolizing ethanol, pausing the fat-burning process.