How Are 0 Calories Possible? The Truth About Zero-Calorie Foods and Drinks

November 5, 2025 •

4 min read

According to U.S. food labeling regulations, a product can be labeled "zero calories" if it contains fewer than 5 calories per serving. This surprising fact reveals that the perception of zero-calorie foods and drinks is often influenced by legal rounding, clever food science, and substances our bodies cannot metabolize.

Quick Summary

Zero-calorie products are possible due to FDA rounding rules, the use of highly potent non-caloric sweeteners, and the inclusion of indigestible substances like certain fibers. The body cannot derive usable energy from these ingredients, resulting in negligible or no caloric impact per serving.

Key Points

FDA Rounding Rule: Products with fewer than 5 calories per serving can be labeled as zero-calorie by law.
Artificial Sweeteners: High-intensity sweeteners like sucralose and aspartame are used in such small, non-metabolized quantities that they contribute virtually no calories.
Indigestible Fiber: Insoluble fiber passes through the digestive system undigested, providing zero calories to the body.
Water Content: Many low-calorie foods like celery are mostly water, a substance that contains no calories.
No Negative Calories: The concept of "negative calorie" foods that burn more energy to digest than they contain is a myth not supported by science.
Metabolic Pathway Bypass: Non-nutritive sweeteners are not processed by the body's energy-yielding metabolic pathways, so no energy is released.
Potential Trace Calories: Be aware that zero-calorie items are not always absolutely free of calories, and overconsumption of multiple servings can add up.

The Science of Calorie-Free Consumption

For many, the concept of a zero-calorie product seems like a health-conscious dream. Whether it's a can of diet soda or a packet of artificial sweetener, these items offer a sweet taste without the energetic cost. The truth behind how 0 calories are possible involves a combination of food regulations, advanced food science, and a simple understanding of how our bodies process energy.

The FDA Rounding Rule: Not Quite Zero

One of the most significant reasons products can claim "zero calories" is the Food and Drug Administration's (FDA) rounding regulations. This rule allows manufacturers to list a product as having zero calories if a single serving contains less than five calories. This is why a single mint or a spritz of cooking spray can carry a zero-calorie label, even though it may contain small, trace amounts of energy from sugars or fats. When consumed in moderation, these minimal calories are virtually insignificant. However, over-consuming multiple servings can add up, turning a "zero-calorie" item into a small caloric intake.

The Role of Non-Nutritive Sweeteners

Many zero-calorie beverages and food additives rely on high-intensity sweeteners that provide sweetness without a significant caloric load. These compounds are hundreds or even thousands of times sweeter than sugar, so only a minuscule, calorically insignificant amount is needed to achieve the desired flavor.

Sucralose (Splenda): Derived from sugar through a chemical process, sucralose is not metabolized by the body for energy. Most of it is excreted without absorption.
Aspartame (Equal, NutraSweet): Composed of two amino acids, aspartic acid and phenylalanine, aspartame is broken down and absorbed. However, because it's so intensely sweet, the quantity used is so small that the caloric contribution is negligible.
Stevia: A natural, plant-based sweetener, stevia leaf extracts are not absorbed or metabolized for energy in the upper digestive tract. Gut bacteria ferment some of it, but the resulting caloric value is minimal.
Acesulfame-K: This synthetic sweetener passes through the body unchanged and is not metabolized for energy.

Indigestible Fiber and Water-Rich Foods

Besides sweeteners, some foods gain their low-calorie status from components our bodies cannot fully break down. Water is the purest form of a zero-calorie substance, and many fruits and vegetables are mostly water. Additionally, fiber plays a crucial role.

Insoluble Fiber: Known as "roughage," insoluble fiber adds bulk but is not digested by the human body, providing effectively zero calories.
Soluble Fiber: While some soluble fiber is fermented by gut bacteria, which produces a few calories, its impact is still minimal compared to other carbohydrates.

These indigestible elements help explain why foods like celery, while containing some energy, result in a very low net calorie gain because of the energy expended to digest their tough, fibrous structure.

The Myth of "Negative Calorie" Foods

The idea that some foods burn more calories to digest than they provide is a common but unproven theory. While the thermic effect of food (the energy used to process it) is real, it is not powerful enough to create a negative calorie balance. For example, the energy required to digest celery is significantly less than the small number of calories it contains. Therefore, a food like celery can be low-calorie, but it doesn't create a caloric deficit simply by being consumed.

Low-Calorie vs. Zero-Calorie: A Comparison


Feature	Low-Calorie Products	Zero-Calorie Products
Calorie Content	Contains 40 calories or less per serving.	Contains less than 5 calories per serving due to rounding.
Primary Sweeteners	May use a combination of low-calorie and zero-calorie sweeteners, or reduced sugar.	Reliant on high-intensity, non-nutritive sweeteners like sucralose or stevia.
Key Ingredients	Typically contain more substantive ingredients like real fruit or sugar alcohols which contain some calories.	Often centered around water, air, or indigestible fibers.
Fullness Factor	Can contain fiber and other nutrients that promote satiety.	Often provide less satiety, as they lack protein, fat, and significant carbohydrates.

Conclusion: The Final Verdict on Zero Calories

In summary, the possibility of a "zero-calorie" product is not a dietary paradox but a carefully regulated reality based on science and law. Our bodies are unable to derive significant energy from non-nutritive sweeteners and indigestible fibers, making their caloric contribution negligible. Paired with FDA rounding rules that allow for less than five calories per serving, this results in products that can be legally labeled as zero-calorie. While most of these items are safe for consumption, understanding the components that make them "calorie-free" empowers consumers to make more informed dietary choices. For truly no-calorie intake, plain water remains the only real option. For further reading on the FDA's specific regulations, see the Electronic Code of Federal Regulations.

Frequently Asked Questions

No, under FDA regulations, a product can be labeled "zero calories" if it contains fewer than 5 calories per serving. The amount is legally rounded down, not necessarily a true zero.

Artificial sweeteners are much sweeter than sugar, so only a tiny, negligible amount is needed. Additionally, many are not metabolized by the human body for energy and pass through the digestive system unused.

No, the concept of negative-calorie foods is a myth. While celery is very low in calories, the energy your body uses to digest it is significantly less than the calories it provides.

Zero-calorie drinks often rely on water and non-nutritive sweeteners. Solid foods, even low-calorie ones, contain some level of macronutrients and fibrous material that provides a small caloric count, even if rounded down.

Most zero-calorie sweeteners are considered safe by regulatory authorities within recommended daily limits. However, ongoing research explores their long-term health effects, and personal tolerance can vary.

Some fibers, particularly insoluble fiber, are not digestible by the human body and therefore contribute no calories. Soluble fiber can be partly fermented by gut bacteria, but the caloric yield is still very low.

While replacing high-calorie items with zero-calorie options can help reduce overall calorie intake, weight loss depends on your total diet and lifestyle. Relying exclusively on zero-calorie products may not provide essential nutrients and can sometimes increase cravings for other sweets.