Why do unhealthy foods have more calories?

January 8, 2026 •

3 min read

A 2019 study published in Cell Metabolism found that people eating an ultra-processed diet consumed around 500 more calories per day compared to those on an unprocessed diet. This reveals the undeniable fact: unhealthy foods are often packed with more calories, but why do unhealthy foods have more calories?

Quick Summary

Unhealthy foods are higher in calories because of their high fat and sugar content and lower water and fiber volume, which increases calorie density. Processing removes nutrients and adds caloric additives, encouraging overconsumption and quicker eating, which contributes to weight gain.

Key Points

Calorie Density: Unhealthy foods have more calories per gram because they are high in fat and sugar, and low in water and fiber.
Fat and Sugar Content: Fat contains more than double the calories per gram compared to carbohydrates or protein, making fat-laden foods very calorie-dense.
Less Fiber and Water: Processing removes water and fiber from foods, reducing their volume and concentrating the caloric content, which reduces satiety.
Faster Absorption: Less digestive energy is needed for processed foods, leaving more net calories for the body to absorb compared to whole foods.
Hyper-Palatability: Food is engineered to be highly palatable, encouraging a faster eating rate and overconsumption by overriding natural satiety signals.
Empty Calories: Many unhealthy foods provide significant energy but little to no essential nutrients, leading to increased cravings and nutrient deficiency.

Understanding Calorie Density: A Matter of Weight and Energy

Calorie density is the number of calories in a specific weight of food. Foods with high calorie density pack many calories into a small serving size, while low-calorie-density foods offer fewer calories for the same weight, or even more volume of food. Unhealthy foods are engineered to be highly calorie-dense, primarily through the addition of fat and sugar, and the removal of water and fiber.

The Macronutrient Culprits: Fat and Sugar

Not all macronutrients are created equal when it comes to caloric load. Fat contains 9 calories per gram, while protein and carbohydrates both provide 4 calories per gram. Unhealthy foods, especially highly processed snacks and fast food, are often loaded with inexpensive fats to enhance flavor and texture. This significantly increases their caloric content without adding much volume, leading to higher energy intake per bite. The prevalence of unhealthy fats and high sugar levels in junk food is well-documented.

The Impact of Water and Fiber Removal

Whole, healthy foods like fruits and vegetables are high in water and fiber, which adds weight and volume without adding calories. This helps you feel full and satisfied. The processing of unhealthy foods, however, often involves removing these elements. Dehydrating and refining ingredients, such as turning potatoes into chips or grains into white flour, removes water and fiber, concentrating the calories in a smaller, lighter package. This makes it easier to overeat before your body's satiety signals are triggered.

The Effect of Processing on Digestion

Food processing not only alters the composition of food but also how your body uses energy to digest it. The 'thermic effect of food' (TEF) is the energy your body uses to digest and absorb food. Your body expends more energy digesting minimally processed, high-fiber whole foods than it does digesting ultra-processed foods. A highly processed food, with its components already broken down, requires very little digestive effort. This means more of the calories consumed are available for energy or storage, whereas the same number of calories from a whole food results in fewer 'net' calories after digestion.

Comparison Table: Healthy vs. Unhealthy Foods


Characteristic	Unhealthy (e.g., Chips)	Healthy (e.g., Baked Potato)
Calorie Density	High	Low to Medium
Fat Content	High (Often unhealthy fats)	Low (Natural fats)
Sugar Content	Often added sugars	Natural sugars only
Water Content	Low (Dehydrated)	High
Fiber Content	Low (Removed during processing)	High (Concentrated in skin)
Satiety	Low (easy to overeat)	High (slower digestion)
Digestive Energy	Low (Less thermic effect)	High (More thermic effect)

The Vicious Cycle: Palatability and Overconsumption

Food manufacturers meticulously formulate unhealthy foods to be 'hyper-palatable,' a perfect combination of fat, sugar, and salt that triggers reward centers in the brain. This intense sensory experience, combined with the faster eating rate facilitated by soft texture, overrides natural satiety cues and drives you to consume more calories than needed. This cycle of high palatability, low satiety, and faster consumption is a key reason for excessive calorie intake when eating junk food.

Conclusion: The Unhealthy Calorie Paradox

The central reason why do unhealthy foods have more calories is not a mystery, but a result of deliberate design and food science. The combination of high-energy macronutrients like fats and sugars, the removal of satiating components like water and fiber, and the engineering of hyper-palatable textures all conspire to make these foods incredibly dense in calories and easy to overeat. Opting for less-processed, whole foods reverses this equation, offering a higher volume of food with more nutrients and less energy, which leads to better health outcomes and sustainable weight management. Making informed choices about the foods we eat involves understanding these fundamental principles of food composition and processing. For more details on ultra-processed diets and their effects, you can refer to research from the National Institutes of Health.

Frequently Asked Questions

Calorie density is the measure of calories in a specific weight or volume of food. High calorie density foods, like most junk food, have many calories in a small package, while low calorie density foods, like vegetables, have fewer calories for the same volume.

Fast food is typically lower in fiber and water and engineered to be eaten quickly. This combination means you consume more calories before your body's satiety signals have a chance to register, making you feel less full.

While not always, processing often increases calorie density. Methods like frying replace water with oil, concentrating calories. Removing fiber also packs more energy into a smaller serving.

Fats contain 9 calories per gram, more than double the 4 calories per gram found in carbohydrates and protein. Unhealthy foods use high amounts of fat to enhance flavor, significantly increasing the overall calorie load.

No. Some high-calorie foods, like avocados, nuts, and salmon, are also nutrient-dense and provide healthy fats, proteins, and vitamins. The key distinction is between 'calorie-dense but nutrient-rich' and 'calorie-dense but nutrient-poor' foods.

Empty calories refer to energy provided by foods that have little to no nutritional value, such as vitamins, minerals, and fiber. Common examples include soda, candy, and many processed baked goods.

A good strategy is to focus on low-calorie-density foods like fruits, vegetables, and whole grains. These are high in water and fiber, filling you up on fewer calories. Limiting processed foods and cooking more at home also gives you control over ingredients.