Have We Bitten Off More Than We Can Chew?

Processed foods have been around for millions of years, since early hominoids first cooked meat over open fires. Humans later learned processing techniques to make food safer, tastier, and longer lasting.

But with the advent of ultraprocessed foods (UPFs), we may have reached the turning point where modern food production methods are coming at an unsustainably steep cost to our health.

UPFs are more durable, cheaper products, but they are often nutrient-deficient and high in calories, sugar, fat, salt, and a host of additives. Emerging evidence suggests that greater UPF consumption can increase the risk for several noncommunicable diseases and related mortality.

Here’s a primer on some of the latest data around UPFs and their potentially adverse role in gastrointestinal (GI) health.

An Increasingly Dominant Food Source

The term UPF was introduced in 2009 by Brazilian nutritionist Carlos Monteiro. Monterio and colleagues established the NOVA classification system, which divides foods into four categories: Unprocessed or minimally processed foods, processed culinary ingredients, processed foods, and UPFs.

Processed foods are manufactured with minimal alterations from their natural state, such as by adding salt, sugar, or oil. Examples include fruit preserved in syrup and vegetables preserved in vinegar or by pickling.

UPFs are highly modified products created through industrial processes. They typically contain multiple additives, preservatives, and artificial ingredients. These foods, built for long shelf lives, include sugar-sweetened beverages, highly processed meat products, flavored yogurts, packaged snacks, and breakfast cereals.

The NOVA system has its critics, though. In a 2022 debate sponsored by the American Society for Nutrition, some experts cautioned that the system was ambiguous and confusing and included otherwise healthy foods, such as plant-based burgers.

Consumption of UPFs is increasing worldwide, with the highest daily energy intake from UPFs among adults occurring in the United States (58%) and the United Kingdom (57%). Among youth, these numbers may be even higher. A large cross-sectional study of US National Health and Nutrition Examination Survey data showed that from 1999 to 2018, the percentage of total energy consumption from UPFs increased from 61.4% to 67% in people aged 2-19 years.

The specific components in UPFs that contribute to various GI diseases remain to be determined. However, preclinical studies have shown that common food additives (eg, sweeteners, coloring agents, emulsifiers, microparticles, or nanoparticles) may adversely affect the gut, including intestinal permeability, intestinal inflammation, and the microbiome.

Risk for Overweight/Obesity and Metabolic Health

The link between UPFs and overweight/obesity has been noted in several studies. One of the first of its kind was a small trial from 2019, in which participants were randomized to either a UPF or minimally processed diet for 2 consecutive weeks, then switched to the alternate diet. It found that during the UPF diet period, patients consumed approximately 500 more calories a day and gained around 2 pounds.

The increased risk for weight gain may even be conveyed to children during pregnancy. A 2022 study of 19,958 mother-child pairs found that the offspring of those who consumed the most UPFs had a 26% higher risk for overweight/obesity than those who consumed the least.

Children who consume high levels of UPFs also have significant alterations in their metabolome, potentially leaving them vulnerable to poorer metabolic health and increased risk for overweight/obesity, according to a 2021 study.

Certain UPFs are associated with an increased risk for type 2 diabetes and therefore may make people susceptible to related GI conditions, such as metabolic dysfunction-associated steatotic liver disease (MASLD). A recent review of several prospective studies found that UPF consumption may be a risk factor for MASLD.

A Compelling Link With Inflammatory Bowel Disease (IBD)

In the United States, the prevalence of IBD has increased over the past decade, with UPF consumption identified as one of the potential causes. This is backed up by a recent meta-analysis, which reported that consuming high levels of UPFs can increase the risk for IBD by 47% in adults.

Higher UPF consumption appears to increase the risk for Crohn’s disease (CD) more than ulcerative colitis (UC). A 2023 meta-analysis established a 71% increased risk for CD associated with high UPF consumption but found no such association with UC. This discrepancy is also apparent in several large prospective studies. Separate studies of 245,112 US health professionals, 187,854 individuals in the UK Biobank, and 413,590 healthy volunteers from eight European countries all found a significant association between higher UPF consumption and CD, but not UC. The health professional analysis found that the UPFs with the strongest correlations with CD risk included ultraprocessed breads and breakfast foods, ready-to-eat/heat meals, and sauces, cheeses, spreads, and gravies.

UPF consumption may also worsen symptoms in those who already have established IBD. A recently published study looked at 135 adults with IBD (34.8% with UC and 65.2% with CD) who consumed 45% of their calories from UPFs. Over 1 year of follow-up, researchers found significantly higher episodes of active disease (14.2 vs 6.2) and active inflammation (1.6 vs 0.6) among patients with UC in the higher tertile of UPF consumption than those in the lower tertile. Unlike the other studies, there was no such association in those with CD.

In a presentation at the annual Crohn’s & Colitis Congress, James D. Lewis, MD, of the University of Pennsylvania in Philadelphia, outlined research pointing to several food additives, including the emulsifiers carboxymethyl cellulose, polysorbate 80, and carrageenan, as potential causes of GI inflammation and IBD.

Most recently, the American Gastroenterological Association issued a clinical practice update recommending that patients with IBD adopt diets low in UPFs, added sugar, and salt and follow a Mediterranean diet rich in fresh fruits and vegetables, monounsaturated fats, complex carbohydrates, and lean proteins, unless contraindicated.

Association With Cancer Risk

High UPF consumption increases the risk of developing cancer overall, as well as overall, ovarian, and breast cancer-related mortality.

The inverse effect also appears to be true. A study from The Lancet Planetary Health found that substituting 10% of UPFs for minimally processed foods lowered the overall cancer risk by 4% and the risk for hepatocellular carcinoma and esophageal squamous cell carcinoma by 27% and 20%, respectively.

Recent meta-analyses present varying results regarding the association between UPF consumption and the risk for certain GI cancers.

A 2023 analysis found that a high intake of UPFs was associated with an increased risk for colorectal cancer (CRC) and pancreatic cancer. Additionally, a meta-analysis of 13 studies listed cancers of the GI tract, including CRC, as among those with the strongest associations, but it noted that further prospective studies were warranted.

The results from three prospective US cohort studies indicated that high consumption of UPFs increased the risk for CRC in men. Certain subgroups of UPFs were also associated with an increased risk for CRC in both men and women.

For patients with existing CRC, continued consumption of UPFs may contribute to increased mortality risk, a new study has found.

On the other hand, a recently published umbrella review of epidemiological meta-analyses concluded that the existing evidence linking UPFs and CRC is weak.

How Clinicians Can Help Patients Avoid These Addictive Foods

Patients may be at a disadvantage when trying to resist the pull of UPFs.

The high carbohydrate and fat content in UPFs produces a dopamine surge in the brain comparable with nicotine.

It also has been estimated that UPF addiction occurs in 14% of adults and 12% of children. Certain UPFs, such as candy and frozen desserts, have been proposed to act as “gateway foods” for teens, pushing them toward other unhealthy dietary practices.

Several policy changes have been proposed to combat the rising toll of UPFs, including taxes on UPFs and mandatory warning labels.

In recent years, several Medscape Medical News contributors have shared their thoughts on UPFs, which clinicians may find helpful in consulting before having their own conversations with patients around these increasingly dominant food staples.

In a 2023 commentary, Caroline Apovian, MD, advised clinicians to question some common assumptions about UPF consumption. Also in 2023, Travis D. Masterson, PhD, provided strategies to help patients deal with stressors that may be driving them to eat certain unhealthy foods. And David Johnson, MD, offered a primer on the possible disease-causing culprits in the Western diet and recommended that clinicians suggest the Mediterranean diet to patients with GI diseases as a healthy, easy alternative.

John Watson is a freelance writer in Philadelphia.

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