Understanding the NOVA Classification System: Why Food Processing Matters for Mental Health

Understanding the NOVA Classification System: Why Food Processing Matters for Mental Health

When we hear the term processed food, it often carries a negative connotation. But the truth is that food processing itself is not the problem. In fact, many foods must be processed to make them safe, edible, and available year-round.

The real question is how much processing has occurred and what has been added during that process.

To better understand these differences, researchers developed the NOVA Classification System, which categorizes foods according to the extent and purpose of processing. This framework has become an important tool in nutrition research, helping scientists examine how different levels of food processing may influence both physical and mental health.

Why Do We Process Food?

Humans have processed food for centuries. Processing helps preserve food, prevent spoilage, improve food safety, and make certain foods edible.

For example, cassava — a staple food in many parts of the world — contains naturally occurring compounds that release cyanide if eaten raw. Through peeling, soaking, and cooking, cassava becomes safe and nutritious.

Similarly, methods such as drying, freezing, pasteurization, and canning help preserve fruits, vegetables, fish, and meat so they remain available throughout the year.

These examples remind us that food processing is both necessary and beneficial. The key difference lies in how foods are processed.

What Is the NOVA Classification System?

The NOVA Classification System groups foods into four categories based on the degree and purpose of processing.

Group 1: Unprocessed or Minimally Processed Foods

These are natural foods that have undergone minimal changes to improve safety or storage without substantially altering their nutritional value.

Examples include:

• Fresh fruits and vegetables
• Whole grains
• Eggs
• Milk
• Fresh meat and fish
• Frozen vegetables
• Pasteurized milk

These foods remain as close as possible to their natural state.

Group 2: Processed Culinary Ingredients

These ingredients are extracted from Group 1 foods and are primarily used for cooking and seasoning.

Examples include:

• Vegetable oils
• Butter
• Sugar
• Salt

Although processed, they are typically consumed in small amounts as part of meal preparation rather than on their own.

Group 3: Processed Foods

These foods are produced by combining minimally processed foods with culinary ingredients such as salt, sugar, or oil.

Examples include:

• Cheese
• Freshly baked bread
• Canned vegetables
• Canned fish
• Fruits preserved in syrup

These foods generally contain only a few added ingredients and still retain much of their original food structure.

Group 4: Ultra-Processed Foods (UPFs)

Ultra-processed foods are industrial formulations made mostly from refined ingredients, food extracts, and additives rather than whole foods.

They often contain:

• Artificial colors
• Flavor enhancers
• Preservatives
• Emulsifiers
• Non-sugar sweeteners
• Stabilizers and other additives

Many manufacturing processes used to produce these foods, such as extrusion, hydrogenation, and hydrolyzation, cannot be replicated in a home kitchen.

Common examples include:

• Soft drinks
• Artificially sweetened beverages
• Instant noodles
• Packaged snacks
• Sugary breakfast cereals
• Frozen ready meals
• Processed meats
• Sweetened desserts

These products are typically designed to be highly convenient, inexpensive, and appealing while offering relatively low nutritional value.

Why Are Ultra-Processed Foods Receiving So Much Attention?

Research has consistently linked diets high in ultra-processed foods with an increased risk of obesity, type 2 diabetes, cardiovascular disease, and several types of cancer.

Today, ultra-processed foods contribute more than half of daily calorie intake in many high-income countries, including the United States, Canada, and the United Kingdom. In several middle-income countries, they account for approximately 20–33% of daily calorie intake, and their consumption continues to increase each year.

As these foods become a larger part of modern diets, researchers are also investigating their potential effects on mental health.

What Did the Research Find?

A large prospective study by Chatpol Samuthpongtorn and colleagues examined whether long-term consumption of ultra-processed foods was associated with depression.

The study followed 31,712 women participating in the Nurses’ Health Study II between 2003 and 2017. Participants, aged 42 to 62 years at the beginning of the study, completed food frequency questionnaires every four years based on the NOVA Classification System. Researchers also collected information about depression diagnoses, antidepressant use, body weight, physical activity, smoking, alcohol intake, chronic diseases, and other lifestyle factors.

The findings showed that participants who consumed the highest amounts of ultra-processed foods were generally more likely to:

• Have a higher body mass index (BMI)
• Smoke more frequently
• Exercise less
• Have diabetes, hypertension, and dyslipidemia

More importantly, participants with the highest ultra-processed food intake had:

• 34% higher likelihood of depression using the study’s stricter definition.
• 49% higher likelihood of depression using the broader definition.

These associations remained significant even after researchers accounted for numerous health and lifestyle factors and examined dietary habits years before depression developed.

Which Ultra-Processed Foods Were Most Strongly Linked to Depression?

Among the different categories of ultra-processed foods, two stood out:

• Artificially sweetened beverages
• Artificial sweeteners

These products showed the strongest association with an increased likelihood of depression.

The researchers also found encouraging evidence that participants who reduced their ultra-processed food intake by at least three servings per day had a lower risk of depression compared with those whose intake remained stable.

Why the NOVA Classification Matters

The NOVA Classification System provides more than a way to organize foods — it offers researchers and healthcare professionals a practical framework for studying how different levels of food processing affect health.

Rather than labeling all processed foods as unhealthy, NOVA helps distinguish between beneficial processing that improves food safety and preservation and ultra-processing that often results in products high in refined ingredients and additives.

Understanding these differences empowers individuals to make more informed dietary choices while helping researchers continue exploring the important relationship between nutrition and mental health.

Key Takeaway

Food processing is an essential part of our food system, but not all processing has the same impact on health. The NOVA Classification System helps us distinguish between minimally processed foods and ultra-processed products, providing valuable insight into how modern diets may influence both physical and mental well-being.

Research suggests that regularly consuming large amounts of ultra-processed foods — particularly artificially sweetened beverages and artificial sweeteners — is associated with a higher likelihood of depression. While more research is needed to better understand the underlying mechanisms, these findings reinforce the importance of choosing more minimally processed, nutrient-rich foods whenever possible to support long-term brain and mental health.

Read full research article on The Center for nutritional psychology.