Is Anything Truly Zero Calories? Debunking the Myths

December 27, 2025 •

4 min read

According to nutrition science, a calorie is a unit of energy derived from macronutrients like carbohydrates, fats, and proteins. This fundamental principle means that any substance providing these nutrients contains energy, leading many to question: is anything truly zero calories?

Quick Summary

Pure water is the only substance with zero calories, but some foods are so low in energy they are considered 'negligible' for intake. The 'negative calorie food' concept is a popular myth, and diet drinks achieve their low-calorie status through non-nutritive sweeteners.

Key Points

Water is the only true zero-calorie substance: It contains no macronutrients and provides no energy to the body.
'Negative calorie foods' are a myth: While some vegetables are very low in calories, the energy required to digest them is less than the energy they provide.
Diet products use non-nutritive sweeteners: Manufacturers achieve zero-calorie labels on sodas and other products by using artificial sweeteners that your body does not metabolize for energy.
FDA labeling allows rounding down: The FDA permits products with fewer than 5 calories per serving to be labeled as zero-calorie, which is why things like cooking spray can be marked as such.
Focus on nutrient density, not just zero calories: A healthy diet is built on a variety of whole foods, not a single-minded pursuit of calorie-free items. Low-calorie, nutrient-dense foods like fruits and vegetables are beneficial but should not be your sole focus.
Beware of the health risks of restrictive diets: Relying entirely on zero-calorie products can lead to a restrictive and unsustainable eating pattern that results in nutritional deficiencies and other health issues.

The Science of Calories: Why Food Contains Energy

To understand if anything is zero calories, you must first grasp what a calorie is. A calorie is a unit of energy that your body uses to function. This energy comes from the three main macronutrients found in food: carbohydrates, proteins, and fats.

Carbohydrates: Contain approximately 4 calories per gram.
Protein: Also contains approximately 4 calories per gram.
Fat: Is the most energy-dense macronutrient, with about 9 calories per gram.

Food and drinks are composed of varying amounts of these macronutrients. Therefore, any edible substance that provides nutritional support, by definition, must contain some calories. The exceptions to this rule are substances that lack these macronutrients entirely or are not metabolized for energy by the human body.

The Sole Exception: Water

Water is the one definitive answer to the question of whether anything is truly zero calories. Composed solely of hydrogen and oxygen, water contains no carbohydrates, protein, or fat. It provides no energy to the body, but it is absolutely essential for survival and plays a crucial role in regulating numerous bodily functions, including digestion, temperature regulation, and nutrient absorption. Flavored sparkling waters, as long as they contain no added sugars or caloric sweeteners, can also be classified as zero-calorie.

Debunking the 'Negative Calorie Food' Myth

A popular dieting belief revolves around the idea of "negative calorie foods"—items that supposedly require more energy to digest than they provide, resulting in a net calorie deficit. Foods like celery, cucumbers, and grapefruit are often cited as examples.

While your body does expend energy to digest food, a process known as the thermic effect of food (TEF), this energy expenditure is only a fraction of the food's total caloric content. The TEF for carbohydrates is about 5–10%, while for protein it's higher at 20–30%. Even for low-calorie, high-fiber foods, the energy required for digestion is far less than the energy the food contains. Therefore, the concept of negative calorie foods is a myth, although these items remain excellent low-calorie, nutrient-rich additions to a healthy diet.

List of Foods Often Mistaken for Negative Calories

Celery: Approximately 14 calories per 100 grams, composed mostly of water and fiber.
Cucumber: Only about 8 calories per half-cup, extremely high in water.
Lettuce: Around 5 calories per cup, another high-water, low-calorie vegetable.
Broccoli: Contains about 54 calories per cup and is packed with vitamins and minerals.

The Role of Artificial and Non-Nutritive Sweeteners

In the modern food landscape, many products are labeled as "zero-calorie" or "diet." These typically contain non-nutritive sweeteners, which are chemical compounds that provide a sweet taste but are not metabolized by the body for energy. The Food and Drug Administration (FDA) in the United States allows products with less than five calories per serving to be labeled as zero-calorie.

Comparison Table: Sweeteners


Sweetener Type	Caloric Content	Sweetness (vs. Sugar)	Common Brands
Sugar (Sucrose)	~16 calories/tsp	1x	Table Sugar
Aspartame	0 calories/tsp*	200x	NutraSweet, Equal
Sucralose	0 calories/tsp*	600x	Splenda
Stevia	0 calories/tsp*	200-300x	Truvia, PureVia
Sugar Alcohols	Low calories/g	Varies	Xylitol, Sorbitol

*While technically containing traces of calories, the amount used is so small that the caloric impact is negligible and can be legally labeled as zero.

The Health Debate Surrounding Artificial Sweeteners

While useful for reducing caloric intake, the long-term health effects of artificial sweeteners are still debated. Some studies suggest a link to increased appetite and potential cardiometabolic risks, while major health organizations consider them safe for moderate consumption. For individuals with a rare genetic disorder called phenylketonuria (PKU), products containing aspartame must be avoided.

Making Smart Choices for a Healthy Diet

Focusing solely on zero-calorie foods is not a sustainable or healthy long-term strategy. The body requires essential macronutrients for energy and function. A balanced diet should prioritize whole, nutrient-dense foods, including those with calories from healthy sources. Very low-calorie foods, especially water-rich fruits and vegetables, can be beneficial for satiety and weight management when part of an overall healthy eating pattern. These foods help you feel full with fewer calories and provide vital nutrients.

Conclusion: The Final Verdict on Zero Calories

In conclusion, the only truly zero-calorie substance is pure water. The idea of "negative calorie foods" is a myth, although many vegetables are incredibly low in calories and nutrient-dense. Manufactured diet products achieve their zero-calorie status by using non-nutritive, artificial sweeteners, which provide sweetness without being metabolized for energy. Ultimately, a balanced and varied diet of whole foods is more important for long-term health than an obsessive focus on finding zero-calorie options. Incorporating plenty of water and nutrient-rich, low-calorie produce is a smart strategy, but it should not come at the expense of other essential nutrients.

How to incorporate healthy, low-calorie foods into your diet

Integrating low-calorie foods can increase satiety and provide nutrients without significantly increasing your total calorie intake. Try filling half your plate with non-starchy vegetables at each meal, or use high-volume, low-calorie ingredients to bulk up soups and salads. For an easy way to stay hydrated, infuse water with fruits like lemon or cucumber for flavor without added calories. For more on the benefits of increased fiber, see this 2015 study from Harvard's Annals of Internal Medicine.

What happens if you only eat zero-calorie foods?

Attempting to subsist solely on zero-calorie items would be detrimental to your health, leading to malnutrition and severe energy deficiency. Your body needs macronutrients to function, and without them, you would experience significant health problems. A diet focused purely on water and artificial sweeteners lacks the vitamins, minerals, fiber, and protein necessary for life.

Frequently Asked Questions

No, the idea that celery and other similar vegetables are 'negative calorie foods' is a myth. While celery is very low in calories, the energy your body expends to digest it is significantly less than the calories it contains.

For all practical purposes, yes. Diet sodas contain artificial sweeteners that are not metabolized by the body for energy. The FDA also allows products with fewer than 5 calories per serving to be labeled as zero-calorie, which covers any negligible amount of energy present.

Yes, high-intensity sweeteners like aspartame and stevia provide a sweet taste without providing calories. They are so potent that only a tiny, negligible amount is needed to sweeten food and drinks.

Water is composed of only hydrogen and oxygen and does not contain any of the macronutrients—carbohydrates, fats, or proteins—that provide energy to the body. This makes it the only substance without any caloric content.

While many vegetables are low in calories due to high water and fiber content, they all contain some energy from carbohydrates. Some starchy vegetables, like potatoes, have significantly more calories than leafy greens or celery.

Yes, incorporating low-calorie and nutrient-dense foods (like vegetables) into your diet can aid weight loss by promoting a feeling of fullness with a minimal caloric load. However, they should be part of a balanced diet, not the only foods you eat.

Cooking sprays can contain trace amounts of oil and therefore calories. The 'zero-calorie' label is possible because the serving size is so small (e.g., a quarter-second spray) that the calorie count falls below the FDA's threshold of 5 calories per serving.