Intermittent fasting (IF) is a dietary approach that cycles between periods of eating and fasting, focusing on when you consume calories rather than what you eat. This practice encourages the body to enter a metabolic state where it shifts from burning glucose to burning stored fat, a process known as ketosis. A central goal of fasting is to keep insulin levels low, as insulin is the hormone that signals the body to store energy and halts the fat-burning state. Cold brew coffee, which is a concentrate of coffee beans steeped in cold water, is a popular beverage, making its impact on the fasted state a frequent question for those following an IF protocol.
Plain Cold Brew Does Not Break a Fast
Plain, black cold brew coffee is generally safe to consume during a fasting window because it contains a negligible amount of calories. A standard 12-ounce serving of unsweetened black cold brew typically contains between 15 and 20 calories, with minimal fat or protein content, and often less than one gram of total carbohydrate. These minimal calories are not enough to trigger a significant insulin response, which is the mechanism that breaks the fast and signals the body to stop burning fat for fuel.
The absence of sugar and protein is particularly important, as carbohydrates and proteins are the macronutrients most likely to stimulate insulin secretion. By not causing a significant insulin spike, black cold brew allows the body to continue its metabolic shift toward utilizing stored body fat for energy. Cold brew’s low caloric density means it maintains the metabolic environment required for processes like ketosis to continue largely uninterrupted.
Furthermore, the caffeine content in cold brew offers an advantage during a fast, as it can help suppress appetite and enhance fat oxidation. This effect helps make the fasting window more manageable by reducing hunger pangs. For individuals whose goal is weight loss and metabolic improvement, consuming black cold brew is compatible with their fasting routine.
Caloric Additions That Immediately Break the Fast
Any addition to cold brew that introduces a significant number of calories or macronutrients will immediately halt the fasted state. Consuming anything over a threshold of 50 calories, and often even less, will break a fast intended for metabolic benefits. This is because the body registers the caloric intake and begins the digestive process, causing an insulin response.
The most common culprits are sugars, syrups, and dairy products. A single teaspoon of sugar or flavored syrup can contain 15 to 20 calories, often entirely from carbohydrates, which cause a rapid spike in blood glucose and subsequent insulin release. Dairy milk and cream contain both carbohydrates (lactose) and protein, both of which are potent insulin stimulators. Adding just a splash of whole milk or half-and-half can easily push the calorie count past the accepted threshold, ending the fast.
Plant-based milks, such as oat, soy, and many almond milks, must be checked carefully, as they often contain added sugars and emulsifiers that contribute to the calorie and carbohydrate count. Even small amounts of these additions will signal the body to exit the fasted, fat-burning state and revert to using the ingested calories for energy. For those fasting, the goal should be to keep the cold brew strictly black and unsweetened to avoid this metabolic shift.
Navigating Non-Caloric and Borderline Additives
The use of zero-calorie sweeteners and pure fats presents a more nuanced discussion for fasters, as their impact depends heavily on the individual’s specific fasting goals. Non-caloric sweeteners like sucralose, aspartame, Stevia, and Monk Fruit do not contain energy, so they do not technically break a fast based purely on calorie intake. However, the intense sweetness can trigger a cephalic phase insulin response, a phenomenon where the body anticipates incoming sugar and releases a small amount of insulin.
For fasters focused on weight loss and metabolic health, the minor or non-existent insulin response from most zero-calorie sweeteners may be acceptable, but those seeking maximum benefits should exercise caution. Furthermore, some research suggests that artificial sweeteners may negatively impact the gut microbiome, which can indirectly affect glucose metabolism over time. Stevia and Monk Fruit are often preferred by fasters because they are considered less likely to provoke a significant metabolic reaction than artificial options.
Pure fats, such as MCT oil, coconut oil, or butter, are sometimes added to cold brew. While these fats are high in calories—a tablespoon of MCT oil contains around 100 calories—they contain zero carbohydrates or protein, meaning they do not cause a significant insulin spike. This practice maintains the state of ketosis, allowing the body to continue burning fat, but it does break a caloric fast. The intake of any calories will inhibit the cellular repair process known as autophagy, which is a goal for many stricter fasters.
Non-caloric flavor enhancers like vanilla or almond extract and ground spices such as cinnamon or nutmeg are considered safe, provided they are used in tiny amounts and do not contain any added sugar. For the strictest fasts, however, even the flavor of these items is avoided to ensure no metabolic or digestive response is triggered. The best approach for a clean fast is plain, black cold brew.