How is it possible for something to be 0 calories?

October 31, 2025 •

3 min read

According to the Food and Drug Administration (FDA), a product can be labeled 'zero calorie' if it contains fewer than 5 calories per serving. This surprising fact reveals that most so-called 'zero calorie' items aren't truly devoid of energy, but rather contain an insignificant amount that regulatory agencies allow to be rounded down. So, how is it possible for something to be 0 calories, or close enough to be labeled that way?

Quick Summary

The possibility of zero-calorie foods lies in low-energy ingredients, indigestible components, and specific labeling regulations. Substances like water, non-caloric sweeteners, and high-fiber foods offer minimal or no metabolizable energy. Labeling laws permit rounding down to zero if a serving contains less than 5 calories, explaining how some products carry the label despite trace amounts of energy.

Key Points

Labeling Regulations: Products with fewer than 5 calories per serving are legally allowed to be labeled as '0 calories' by the FDA, a key reason for their existence.
Indigestible Ingredients: The human body cannot extract energy from certain compounds, such as dietary fiber or the molecules in many artificial sweeteners, making them effectively calorie-free.
Water Content: Many low-calorie vegetables contain high percentages of water, which is naturally calorie-free and adds bulk, contributing to their low energy density.
Artificial Sweeteners: These non-nutritive compounds mimic the taste of sugar but are not metabolized by the body, so they provide sweetness without energy.
Serving Size Manipulation: Manufacturers can define a serving size small enough to ensure the calorie count falls below the 5-calorie threshold, allowing for a '0 calorie' claim.
Not Always Nutrient-Free: While processed zero-calorie foods offer no nutrients, many naturally low-calorie, high-fiber vegetables still provide essential vitamins and minerals.

The Science of Calories and Energy

To understand how something can be '0 calories,' we must first grasp what a calorie is. A calorie is a unit of energy derived from food. The macronutrients that provide energy—carbohydrates, proteins, and fats—contain a specific number of calories per gram. If a substance lacks these energy-yielding macronutrients in a form our bodies can digest, it provides zero or near-zero calories.

Indigestible Compounds and Artificial Sweeteners

One primary method for creating zero-calorie products is using compounds that our digestive systems cannot break down for energy. Artificial sweeteners are a perfect example. While they stimulate the taste receptors on our tongue to perceive sweetness, their chemical structures prevent the body from metabolizing them into usable energy. For instance, sucralose is a modified sugar molecule where specific hydroxyl groups are replaced with chlorine atoms, making it indigestible yet hundreds of times sweeter than regular sugar.

The Role of Fiber and Water

Fiber and water are two naturally occurring components that contribute to the near-zero calorie status of many foods. Water is essential for hydration and contains no calories. Fiber, particularly the indigestible kind, is a type of carbohydrate that our bodies cannot fully process. While it provides bulk and aids digestion, humans lack the necessary enzymes to extract significant energy from it, meaning much of it passes through our system without being converted to calories. This is why foods like celery, lettuce, and cucumbers, which are high in water and fiber, are often cited as 'almost zero-calorie' foods.

Labeling Laws and the 'Rounding Down' Rule

The FDA allows food manufacturers to list a product as '0 calories' if it contains fewer than 5 calories per serving. This regulatory guideline is a major reason behind the existence of zero-calorie items. For example, a single Tic Tac mint has less than 0.5 grams of sugar per serving, which rounds down to zero calories on the nutritional label. Similarly, cooking sprays and other condiments may be able to list zero calories due to a very small suggested serving size.

Natural vs. Artificial Zero-Calorie Options


Feature	Natural Zero-Calorie Options	Artificial Zero-Calorie Options
Source	Derived from plants (stevia) or are naturally indigestible (water, fiber in vegetables).	Synthetically created or modified in a lab (sucralose, aspartame).
Caloric Value	Truly zero (water) or contain minimal, indigestible calories (high-fiber vegetables).	Effectively zero per serving due to high potency and low quantity, or by being non-metabolizable.
Effect on the Body	Provide hydration and fiber, supporting digestive health and satiety.	Trick the brain into perceiving sweetness, which can potentially confuse metabolic processes.
Nutritional Content	Often rich in vitamins and minerals (leafy greens, vegetables).	Offer little to no nutritional value beyond taste.
Examples	Water, celery, iceberg lettuce, cucumber, shirataki noodles, stevia.	Diet sodas, sugar-free gum, diet dressings, some flavored gelatin.

The Health Implications

While zero-calorie foods and drinks can assist in managing calorie intake, it is crucial to understand their nutritional value. Natural options like water and fibrous vegetables are beneficial due to their hydrating and digestive properties. However, relying heavily on processed, artificially sweetened products can have drawbacks. Some studies suggest that the artificial sweetness can confuse the body, potentially impacting appetite and leading to cravings for more calorically dense foods. Furthermore, these products rarely offer the essential nutrients found in whole foods. A balanced approach incorporating nutrient-dense, low-calorie options is generally healthier than solely seeking out zero-calorie processed foods.

Conclusion

In summary, the possibility of something being 0 calories is rooted in two main principles: regulatory rounding and the use of indigestible compounds. Most so-called 'zero calorie' foods, aside from water, contain trace amounts of calories that are legally rounded down on nutrition labels. Processed zero-calorie items rely on artificial sweeteners that the body cannot metabolize for energy. Natural, nearly zero-calorie foods like vegetables contain high amounts of indigestible fiber and water. While these options can aid in weight management, a critical understanding of both labeling regulations and the source of the 'zero calories' is essential for making informed dietary choices.

: https://www.reddit.com/r/explainlikeimfive/comments/6vjoja/eli5_how_can_a_food_have_0_calories/ : https://www.reddit.com/r/explainlikeimfive/comments/3pdt47/eli5_how_does_diet_soda_have_0_calories/ : https://waldenfarms.com/blogs/blog-posts/understanding-zero-calorie-vs-trace-calorie-labels-what-you-need-to-know : https://www.medicalnewstoday.com/articles/263028

Frequently Asked Questions

No, most products labeled 'zero calorie' are not truly calorie-free. According to regulations in the US, manufacturers can legally label a product as '0 calories' if it contains fewer than 5 calories per serving.

A product can be 'zero calorie' by containing ingredients that the human body cannot metabolize for energy, such as indigestible fibers, water, and artificial sweeteners like sucralose and aspartame.

Diet sodas and other drinks sweetened with artificial sweeteners contain an insignificant amount of calories. Since these sweeteners are hundreds of times sweeter than sugar, only a tiny amount is needed, keeping the total calorie count per serving below the legal threshold for rounding to zero.

Natural zero-calorie options, like water and fibrous vegetables, often provide other nutritional benefits and rely on indigestible components. Artificial options use synthetically created sweeteners that offer no nutritional value beyond taste.

No, you cannot survive or lose weight healthily by eating only zero-calorie foods. A varied diet with adequate protein, fats, and carbohydrates is necessary for all bodily functions. Relying solely on zero-calorie foods can lead to nutrient deficiencies and health problems.

Some vegetables, like celery and cucumber, are often called 'zero calorie' because they are mostly water and indigestible fiber. While they do contain a few calories, the amount is so low that it is sometimes colloquially, and misleadingly, described as zero.

The concept of 'negative calorie' foods is a myth. While the body does expend some energy to digest food, known as the thermic effect of food, this amount is not high enough to create a negative calorie balance. The energy burned is always less than the energy contained in the food itself.