How is it possible for something to have zero calories?

December 7, 2025 •

4 min read

According to the U.S. Food and Drug Administration (FDA), a product can be labeled as "zero-calorie" if it contains fewer than 5 calories per serving. This regulatory nuance is one of the key ways it is possible for something to have zero calories, alongside ingredients our bodies can't metabolize, such as certain fibers and artificial sweeteners.

Quick Summary

This article explores the scientific principles and regulatory rules behind zero-calorie products, explaining how indigestible compounds, regulatory rounding, and water content result in minimal or no energy for the human body.

Key Points

Regulatory Rounding: The FDA permits food products with fewer than 5 calories per serving to be legally labeled as having zero calories, a practice that enables many low-calorie items to bear the claim.
Indigestible Molecules: Artificial sweeteners like sucralose and saccharin are not metabolized by the body's digestive system, providing a sweet taste without any caloric energy.
Fiber's Role: Insoluble fiber, found in many vegetables and whole grains, passes through the digestive tract largely untouched, meaning the body cannot extract any calories from it.
Minimal Absorption: Certain sugar alcohols, such as erythritol, are poorly absorbed by the body, resulting in a very low caloric value compared to traditional sugars.
Water as the Baseline: As an inorganic substance without energy-providing macronutrients, pure water serves as the only substance that is a true and absolute source of zero calories.
Informed Choices: It is crucial for consumers to understand the distinction between truly zero-calorie items and those labeled as such due to serving size regulations to make truly informed decisions about their dietary intake.

A common point of curiosity for many people, the concept of a "zero-calorie" food or drink seems almost counter-intuitive, yet it is a well-established fact in the modern diet. The answer lies in a combination of food science, human biology, and government regulation. There isn't just one reason why this is possible; rather, a few different mechanisms contribute to the creation and labeling of these products.

The Regulatory "Rounding Down" Rule

One of the most significant reasons a product can carry a zero-calorie label is a regulation-driven loophole. The U.S. Food and Drug Administration (FDA) allows food manufacturers to list a product as having zero calories if it contains fewer than five calories per serving. For example, a single Tic Tac mint has less than 0.5 grams of sugar, allowing it to be rounded down to zero calories per serving. Similarly, tiny servings of cooking spray contain a minuscule amount of fat, allowing them to be labeled as calorie-free. The total calories from an entire container could be significant, but the per-serving rule permits the zero-calorie claim.

Indigestible Compounds That Trick Your Taste Buds

Another major factor in creating zero-calorie products is the use of substances that taste sweet but are not metabolized for energy by the human body. These substances are often a key component of diet sodas, sugar-free candies, and other low-calorie options.

Artificial Sweeteners and Non-Nutritive Sweeteners

Artificial sweeteners, also known as non-nutritive sweeteners (NNS), provide intense sweetness with virtually no calories. Their molecules are designed to bind with the sweet taste receptors on your tongue, sending a signal to the brain that the food is sweet. However, unlike sugar, their molecular structure is generally not recognizable by the enzymes in our digestive system. Common examples include:

Sucralose (Splenda): A modified sugar molecule that passes through the body largely undigested.
Saccharin (Sweet'N Low): A long-used sweetener that is not metabolized for energy.
Aspartame (NutraSweet, Equal): While it does contain calories (4 kcal/gram, like sugar), it is so intensely sweet (200 times sweeter than sugar) that only a tiny amount is needed to achieve the desired sweetness, making its caloric contribution negligible per serving.

The Role of Fiber

Fiber is a type of carbohydrate that our bodies cannot fully digest. It comes in two main forms, with different caloric impacts:

Insoluble Fiber: This fiber does not dissolve in water and passes through the digestive tract largely intact. Because it is not broken down or absorbed, it provides zero calories. It adds bulk to food and aids in digestion. Foods high in insoluble fiber include wheat bran and certain vegetables.
Soluble Fiber: This fiber dissolves in water and is fermented by bacteria in the large intestine. This fermentation process produces short-chain fatty acids, which our bodies can use for a small amount of energy. A general rule of thumb is to count about 2 calories per gram of soluble fiber. However, this is significantly less than the 4 calories per gram from other carbohydrates and is often already accounted for in nutrition labels.

Low-Calorie Sugar Alcohols

Another category of sweeteners, sugar alcohols (or polyols), contain a fraction of the calories of regular sugar due to poor absorption. Common sugar alcohols include Erythritol, Xylitol, and Sorbitol. For instance, Erythritol provides only about 0.2 calories per gram because it is mostly absorbed in the small intestine and then excreted unchanged in urine. Other sugar alcohols are incompletely absorbed and metabolized, resulting in fewer calories per gram than sugar, but generally not zero.

The Truest Zero: Water

At the most fundamental level, the simplest and most common zero-calorie substance is water. As an inorganic compound, it does not contain any of the macronutrients—carbohydrates, proteins, or fats—that our bodies break down for energy. It is essential for life but provides no energy, making it a true zero-calorie substance.

Comparison of Zero-Calorie Mechanisms


Mechanism	Examples	How it Works	Caloric Impact	Common Concerns
Regulatory Rounding	Diet soda, cooking sprays, low-calorie mints	FDA rule allows products under 5 calories/serving to be labeled as zero.	Technically low-calorie, but labeled zero due to serving size.	Consumer deception over actual total calories if multiple servings are consumed.
Indigestible Sweeteners	Sucralose, Saccharin, Stevia	Molecules are not metabolized by the body for energy, passing through undigested.	Truly zero calories, as no energy is extracted.	Potential impact on gut health and long-term health effects are still being studied.
Insoluble Fiber	Wheat bran, celery	Passes through the digestive system without being broken down or absorbed.	Truly zero calories, as no energy is extracted.	Can cause digestive discomfort in large amounts.
Low-Absorbed Sugar Alcohols	Erythritol	Poorly absorbed by the small intestine, providing minimal energy.	Very low calories, but not truly zero.	Can cause bloating, gas, and diarrhea if consumed in excess.
Water	Plain water	Inorganic compound with no energy-providing macronutrients.	Truly zero calories.	None, besides potential for electrolyte imbalance with extreme overconsumption.

Conclusion

The ability for something to have zero calories is a nuanced topic that combines scientific reality with regulatory flexibility. It is possible due to the use of compounds our bodies cannot digest for energy, like certain sweeteners and insoluble fiber, and due to government rules that allow for the rounding down of low-calorie products. While these items can be useful tools for managing calorie intake, it is important to remember that they are not a substitute for a balanced diet rich in nutrient-dense, whole foods. As research continues on the long-term effects of artificial ingredients, understanding the science behind the label is key to making informed dietary decisions.

For additional information on nutrition labeling, you can review the FDA's guidance on the topic.

Frequently Asked Questions

The health effects of artificial sweeteners are a topic of ongoing research and debate. While health authorities generally consider them safe for consumption in moderation, some studies raise questions about their impact on gut health and metabolism. It is best to consult a dietitian for personalized advice.

No, it's not advisable to over-rely on zero-calorie foods. Some, like celery or cucumbers, can add nutrients and hydration, but heavily processed zero-calorie items often lack beneficial nutrients. Consuming too many can also lead to digestive issues and, paradoxically, increase cravings for sweets and other foods.

The zero-calorie label on diet soda is due to the tiny amount of intensely sweet artificial sweetener used. While a packet of aspartame does contain a small amount of carbohydrates (and thus calories), the amount used in a single can of diet soda is negligible enough to be rounded down to zero per serving according to FDA regulations.

No, the concept of a 'negative calorie' food is a myth. While it's true that your body uses a small amount of energy to digest food (the thermic effect of food), it's never enough to negate the calories provided by even very low-calorie items like celery. These foods are simply very low in caloric density.

Sugar alcohols like xylitol and sorbitol contain calories because they are partially metabolized by the body. Their absorption is incomplete, so they provide fewer calories per gram than regular sugar, but they are not calorie-free.

Yes, water is the only truly zero-calorie substance and beverage. It provides no energy because it is an inorganic compound, unlike the organic macronutrients (carbohydrates, fats, and proteins) that provide energy.

In many countries, nutrition labels already account for the small number of calories from digestible fiber. While insoluble fiber (zero calories) passes through, the caloric contribution from soluble fiber is typically included within the total carbohydrate count, so you don't need to deduct it yourself.