Two new studies suggest that ‘convenience’ foods may come at a high cost to our health.

Two large studies that followed participants for decades have provided further evidence that the foods we eat — and don’t eat — can have significant health consequences. The research, published August 31 in the BMJ, found that people who consumed higher amounts of “ultra-processed” foods were at greater risk of cardiovascular disease, bowel (colorectal) cancer, and early death.

What are ultra-processed foods? They include items like hot dogs, lunch meat, baked goods, salty snacks like chips, and sugary drinks, along with prepackaged ready-to-eat or microwave meals, which can contain more unhealthy fats and lots of sodium.

According to researchers, these findings add further support for policies that limit ultra-processed foods and promote unprocessed or minimally processed foods to improve public health worldwide.

In the first study, researchers examined the association between the consumption of ultra-processed foods and the risk of colorectal cancer in U.S. adults using data from 46,341 men and 159,907 women who had participated in one of three large studies of U.S. health professionals: the Nurses’ Health Study (1986–2014), the Nurses’ Health Study II (1991–2015), and the Health Professional Follow-Up Study (1986–2014).

“We started out thinking that colorectal cancer could be the cancer most impacted by diet compared to other cancer types,” said the lead author, Lu Wang, PhD, a postdoctoral fellow at the Friedman School of Nutrition Science and Policy at Tufts University in Boston, in a press release. “Processed meats, most of which fall into the category of ultra-processed foods, are a strong risk factor for colorectal cancer. Ultra-processed foods are also high in added sugars and low in fiber, which contribute to weight gain and obesity, and obesity is an established risk factor for colorectal cancer,” she said.

Previous studies have linked ultra-processed foods to higher risk of obesity, high blood pressure, cholesterol, and some cancers, but there is not much research that examines the association between ultra-processed food intake and colorectal cancer risk, according to the authors.

This study followed participants for 24 to 28 years and controlled for many medical and lifestyle factors, giving researchers a unique opportunity to see the potential long-term impact of diet.

“Cancer takes years or even decades to develop, and from our epidemiological studies, we have shown the potential latency effect — it takes years to see an effect for certain exposure on cancer risk,” said the co-senior author Mingyang Song, ScD, an assistant professor of clinical epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, in the press release. “Because of this lengthy process, it’s important to have long-term exposure to data to better evaluate cancer risk,” he said.

Everyone included in the analysis had their dietary intake assessed every four years using detailed food frequency questionnaires. To measure the association of the level of processing with cancer risk, researchers assigned foods to one of four groups: unprocessed or minimally processed foods, processed culinary ingredients, processed foods, and ultra-processed foods.

Investigators found that compared with those in the lowest fifth of ultra-processed food consumption, men in the highest fifth of consumption had a 29 percent higher risk of colorectal cancer, which remained significant after controlling for body mass index (BMI) and dietary quality.

The strongest association between colorectal cancer and ultra-processed foods among men came from meat, poultry, or fish-based ready-to-eat products, including some processed meats like sausages, bacon, ham, and fish cakes.

“The findings are by no means a surprise, especially as it relates to processed meat,” says Otis Brawley, MD, a professor of oncology at Johns Hopkins Medicine in Baltimore and a globally recognized expert in cancer prevention and control who was not involved in the research.

“It’s estimated that processed meat actually causes 34,000 deaths per year worldwide,” Dr. Brawley says. An analysis of 10 studies concluded that every 50 gram portion of processed meat eaten daily increased the risk of colorectal cancer by 18 percent, he notes.

Although the latest study provides insight into how self-reported food intake relates to the incidence of colorectal cancer, further research is needed to confirm what is happening that may be contributing to the increased risk, says Amanda Bode, RDN, of Cleveland Clinic’s Center for Human Nutrition, who was not involved in the research. “Perhaps it is the lack of whole fruits, vegetables, and grains that alters the microbiota leading to inflammation. Or is it that the additives and preservatives used in processed foods result in damage to the gut?” she says.

Only about 1 in 8 adults consume the recommended 1.5 to 2 cups of fruit each day, and only 1 in 10 eat the recommended 2 to 3 cups of vegetables each day, including legumes, according to data from a Centers for Disease Control and Prevention (CDC) report published in January 2022.

Interestingly, no association was observed between overall ultra-processed food consumption and the risk of colorectal cancer among women.

It could be that the composition of the ultra-processed foods consumed by women could be different from that for men, said the researchers. For example, some foods considered ultra-processed, such as yogurt, actually reduced the risk of colorectal cancer.

It isn’t clear why the study has shown differences in risk and intake between men and women, says Bode. There may be underreporting of ultra-processed foods, or women could have made better choices within the range of ultra-processed foods, or there may be female hormones that are protective against colorectal cancer, she says.

In the second study, researchers used two different measures to compare “nutrient poor” foods and beverages that were high in sugar and saturated or trans fats with "ultra-processed" foods and drinks to determine how each category impacted the development of chronic disease (especially heart disease) and early death.

A total of 22,895 Italian adults from the Moli-Sani Project were included in the study; 52 percent were women, and the average age of participants was 55 years old.

Researchers considered both the quality and quantity of what was consumed, and deaths were measured over a 14-year period (2005 to 2019), taking underlying medical conditions into account.

Results showed that those eating the least healthfully had a 19 percent higher risk of death from any cause and a 32 percent higher risk of death from cardiovascular disease than those who ate the healthiest diet.

The nutrient-poor and highly processed foods added about the same amount of risk, with processed foods being associated with slightly worse outcomes.

The results confirmed that the consumption of nutrient-poor or ultra-processed foods independently increased the risk of mortality, in particular from cardiovascular diseases, said the first author, Marialaura Bonaccio, PhD, an epidemiologist in the department of epidemiology and prevention at the IRCCS Mediterranean Neurological Institute in Pozzilli, Italy, in a press release. But when researchers took into account both the overall nutritional composition of the diet and its degree of processing, it turned out that processing was paramount in determining the risk of mortality, she said.

Over 80 percent of the foods classified as unhealthy are also ultra-processed, she noted. “This suggests that the increased risk of mortality is not due directly (or exclusively) to the poor nutritional quality of some products, but rather to the fact that these foods are mostly ultra-processed.”

These findings are to be expected, says Brawley. There are a number of factors at work — one of which is that many processed foods are high in calories and contribute to obesity, a risk factor for many diseases, he says.

A study published in October 2020 in the European Heart Journal: Quality of Care and Clinical Outcomes concluded that two-thirds of heart-disease-related deaths worldwide can be linked to food choices — the authors estimated that six million deaths could have been avoided through better diets.

Both the Tufts study and the Italian study were observational and didn't establish cause, and their limitations include the possibility that some of the risks for disease may be due to unmeasured factors, according to the authors.

But these studies along with many other well-designed cohort studies have consistently shown these associations, says Brawley. “The only way to go further would be long-term prospective randomized trials, which would be impossible to run and possibly unethical. You cannot give a substance you believe is definitely carcinogenic to a group of people in a clinical trial to see if they get cancer,” he points out.

In November 2021, the American Heart Association released updated dietary guidelines — the first in 15 years. The new guidance emphasized the importance of a healthy and sustainable pattern of eating rather than drastic — and usually short-lived — changes.

Alice H. Lichtenstein, DSc, the chair of the writing group for the AHA statement, a senior scientist, and the director of the cardiovascular nutrition team at the USDA Human Nutrition Research Center on Aging at Tufts University in Boston, offers the following advice.

Shop around. Find out what different foods are available in your neighborhood at a price point you’re willing to pay.

Find the healthiest versions of the foods you eat regularly. Take time to compare different foods that you enjoy. “For example, if you like to eat soup or crackers — look at labels to find choices that are lower in sodium, added sugars, or unhealthy fats.”

Check the internet for nutritional information on takeout or prepared meals. Many places have nutritional information for different items. As a general rule, even for prepared foods or takeout foods, the less processed, the better.

When faced with options, keep heart-healthy guidelines in mind. If you’re faced with choices about bread or rice, choose whole grains when possible. When you put together a salad, focus on more vegetables and fewer items like bacon bits or heavy dressings.

Enjoy your food. Frequently people think that if a food is healthy, it won't taste good, says Dr. Lichtenstein. “Not true. There’s so much of a range and flexibility in healthy choices. You should be able to find one that you enjoy.”

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