Are ultra-processed foods a public health hazard?

Ultra-processed foods are now tied to a wide range of diseases — I'll pull the latest evidence on whether they amount to a public health hazard.

Based on current evidence, ultra-processed foods (UPFs) are increasingly described as a public health hazard - but with important nuance.

What are ultra-processed foods?

There is no single legal definition, but research uses the NOVA classification system developed in Brazil in 2009 and recognized by the World Health Organization (WHO). NOVA divides foods into four groups:

NOVA Group 4 - Ultra-Processed Foods - refers to "industrial formulations made entirely or mostly from substances extracted from foods (oils, fats, sugar, starch, and proteins), derived from food constituents (hydrogenated fats and modified starch), or synthesized in laboratories".

Examples include ready-to-eat/heat mixed dishes, savoury snacks, sweets and desserts, sugar-sweetened and artificially sweetened beverages, processed meats like chicken nuggets, packaged breads with additives, and flavoured yogurts.

This category is broader than its worst members. Fortified breakfast cereal, canned beans, and plant-based milk all fall within it.

What does the large-scale evidence show?

The most comprehensive synthesis to date is a 2024 BMJ umbrella review of existing meta-analyses by Lane et al.:

Graded by pre-specified evidence classification:

Convincing evidence (class I) supported direct associations between greater UPF exposure and higher risks of:

Highly suggestive (class II) evidence indicated greater exposure was directly associated with higher risks of:

Of the remaining 34 pooled analyses, 21 were graded as suggestive or weak and 13 as no evidence.

Other large studies summarized in the same field find similar patterns:

The BMJ authors concluded:

> Greater exposure to ultra-processed food was associated with a higher risk of adverse health outcomes, especially cardiometabolic, common mental disorder, and mortality outcomes

> These findings provide a rationale to develop and evaluate the effectiveness of using population based and public health measures to target and reduce dietary exposure to ultra-processed foods for improved human health

Why might they be harmful? Proposed mechanisms

There probably isn't one single mechanism. Several factors may work together.

Experimental evidence supports that processing itself matters:

A 2019 inpatient randomized trial fed 20 adults diets matched for calories, sugar, fat, fiber and macronutrients - people ate about 500 extra calories per day on the ultra-processed diet and gained weight.

A 2025 Cell Metabolism randomized crossover trial showed an ultra-processed diet raised body weight and worsened cholesterol ratios even when calories were matched exactly to an unprocessed diet. Healthy young men were switched between diets with total calories carefully matched - even with calories held constant, the ultra-processed phase led to higher body weight and worse LDL-to-HDL ratio, plus hormone shifts and detectable pollutant differences including a rise in a phthalate byproduct linked to packaging.

The authors summarized: this is the study that finally answers the "but is it really the processing, or just the sugar and fat?" question - sugar, fat and total calories were controlled for, the processing itself still changed body weight and cholesterol.

The nuance: Is every UPF equally hazardous?

Major recent critiques argue that processing itself is not inherently harmful and that nutritional quality matters more.

Therefore:

> Advising people to universally 'avoid ultra-processed foods' can lead to lower diet quality since healthy ultra-processed foods are beneficial and unhealthy minimally processed foods are detrimental

Limitations of current evidence must also be acknowledged: Using the GRADE framework, 22 pooled analyses were rated as low quality, with 19 rated as very low quality and four rated as moderate quality. Most large studies are observational and cannot fully exclude confounding by income, lifestyle, or overall dietary pattern, though randomized trials are beginning to address causality.

Conclusion: Hazard at the population level

Public health bodies including WHO and the Lancet 2025 three-paper series now treat high UPF consumption as a cross-cutting driver of health inequities and chronic disease worldwide. At current levels - where UPFs account for 50-60% of calories in high-income countries - the consistent associations with obesity, type 2 diabetes, cardiovascular mortality, depression/anxiety, and all-cause mortality, plus plausible mechanisms and emerging experimental support, lead most experts to call high UPF diets a public health hazard warranting population-level measures (reformulation, labeling, taxation, school food standards, and dietary guidelines emphasizing minimally processed foods).

However, the hazard is not uniform: not all foods classified as ultra-processed are equally harmful. Sugary drinks, processed meats/ready-to-eat meat products, and packaged desserts show the strongest and most consistent links to death, while fortified whole-grain cereals, canned beans, or unsweetened plant-based yogurts classified as UPFs may be part of a healthy diet. The key public health message emerging is to prioritize overall diet quality - rich in whole grains, fruits, vegetables, nuts, legumes and healthy plant oils - and reduce especially the most nutrient-poor, hyper-palatable UPFs, rather than to treat every packaged food as equally toxic.