Ultra-processed foods: obesity and weight gain

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Scientific research shows a strong association between ultra-processed foods and obesity. (Photo credit: Ishak Robin/Unsplash)

During the last fifty years, the obesity rate across the globe has nearly tripled. Today in the U.S., more than 2 in 3 adults are either overweight or obese, according to the Centers for Disease Control and Prevention

The United States consistently ranks among the countries with the highest obesity rates in the world. Since the 1970s, the rate of childhood obesity has tripled in the U.S., with 1 out of 5 American kids currently obese.

Americans are among the highest consumers of ultra-processed food (UPF) in the world; more than half of our calories come from UPFs. Typically, these foods are highly palatable and often high in fat and sugar or sweeteners, like sucralose and aspartame. They also usually contain additives and preservatives.

Such foods include sugary sodas and drinks, fruit-flavored juices and yogurts, chips, cookies, deli meats and sausage, ice cream, frozen meals, canned soups, and much more.

Many experts argue that the increase in UPF consumption has been an important contributor to the obesity epidemic in the country and throughout the world. 

The following scientific research shows that ultra-processed foods are linked, in both children and adults, to weight gain, obesity, higher body mass index (BMI), and an increased waist circumference.

Obesity and weight gain in children

Published in JAMA Pediatrics in 2021, researchers of a cohort study of more than 9,000 British children found that “growth trajectories of body mass index, fat mass index, weight, and waist circumference from 7 to 24 years of age were greater among children with the highest (vs lowest) quintile of UPF consumption.” The researchers concluded: “These findings suggest that radical and effective public health actions that reduce children’s exposure to and consumption of UPF and remove barriers to accessing minimally processed foods are urgently needed to counteract the growing burden of obesity in England and globally.”

In a multi-country study of children published in the Obesity Review in 2022, researchers examined ultra-processed food consumption of children across eight countries. They found that ultra-processed food consumption “ranged from 18% of total energy intake among preschool children in Colombia to 68% among adolescents in the United Kingdom,” and that, “in almost all countries and age groups, increases in the dietary share of ultraprocessed foods were associated with increases in energy density and free sugars and decreases in fiber, suggesting that ultraprocessed food consumption is a potential determinant of obesity in children and adolescents.” They concluded: “Effective global policy action to address growing ultraprocessed food consumption and childhood obesity is urgently needed.”

A systematic review and meta-analysis published in Advances in Nutrition included more than 26,000 citations to evaluate unhealthy food consumption and the risk in children of being overweight and having obesity. The research, published in 2022, found evidence that indicated “consumption of sugar-sweetened beverages (SSBs) and unhealthy foods in childhood may increase BMI/BMI z-score, percentage body fat, or odds of overweight/obesity.” In a subset of studies, meta-analyses “indicated a positive association between sugar-sweetened beverage intake and percentage body fat.” 

In a systematic review of 26 studies published in 2018 in the journal Public Health Nutrition, researchers examined how ultra-processed foods affect weight gain and obesity in children. The study authors found “that most studies [had] positive associations between consumption of ultra-processed food and body fat during childhood and adolescence.”

Obesity and weight gain in adults

In an observational study published in 2016 in the American Journal of Clinical Nutrition, researchers included more than 8,000 Spanish adults who were not overweight or obese. After following up for a median of 8.9 years later, there were 1939 participants who were overweight or obese. They found “participants in the highest quartile of ultraprocessed food consumption were at a higher risk of developing overweight or obesity than those in the lowest quartile of consumption.”

Published in 2020 in PLoS Medicine, a prospective analysis of more than 100,000 people based in France found, after adjusting for several lifestyle and demographic factors, people who ate more ultra-processed food were more likely to experience weight gain, along with being at higher risk of being overweight or obese. The researchers wrote: “These results remained statistically significant after adjustment for the nutritional quality of the diet and energy intake.” They continued: “This study contributes to the mounting evidence on the link between food processing and health.”

In a randomized control trial published in 2019 in Cell Metabolism, researchers examined whether ultra-processed foods “affect energy intake in 20 weight-stable adults.” Study participants stayed in a clinical center for four weeks, where they were told to eat an ultra-processed or unprocessed diet for 2 weeks, and then eat the alternative diet for the following 2 weeks; the participants were told to eat as much or as little as they wanted of their meals. Researchers found that “Energy intake was greater during the ultra-processed diet, with increased consumption of carbohydrate and fat, but not protein. Weight changes were highly correlated with energy intake, with participants gaining 0.9 ± 0.3 kg during the ultra-processed diet and losing 0.9 ± 0.3 kg during the unprocessed diet.”

In a 2020 meta-analysis published in the International Journal of Obesity, researchers performed a literature search that included 14 studies that investigated the link between ultra-processed foods and weight. They found a “significant association” between ultra-processed food consumption and being overweight or obese.

In a systematic review of 17 prospective studies published in the journal Nutrients, scientists examined the risk of ultra-processed food consumption and several adverse health effects, including obesity. They wrote that “substantial agreement emerged among the studies in defining UPF consumption as being associated with the incident risk of general and abdominal obesity.”

In a study published in the European Journal of Nutrition in 2021, researchers examined obesity risk and ultra-processed food in UK adults. After participants self-reported their diets, and then measured BMI, waist circumference, percentage of body fat, and adjusted for lifestyle and other factors. Study authors wrote: “Participants in the highest quartile of ultra-processed food consumption had significantly higher risk of developing overall obesity and abdominal obesity. They had a higher risk of experiencing a ≥ 5% increase in BMI, waist circumference and percent body fat, than those in the lowest quartile of consumption.” They concluded: “Our findings provide evidence that higher consumption of ultra-processed food is strongly associated with a higher risk of multiple indicators of obesity in the UK adult population. Policy makers should consider actions that promote consumption of fresh or minimally processed foods and reduce consumption of ultra-processed foods.”

Canadian researchers found that ultra-processed food was associated with obesity, even after adjusting for confounding factors. The cross-sectional study, published in the Canadian Journal of Public Health in 2018, included nearly 20,000 people and showed that UPFs made up nearly half of the participants’ daily caloric intake.The study authors wrote: “After adjusting for confounding factors, individuals in the highest quintile of ultra-processed food consumption were 32% more likely of having obesity compared to individuals in the first quintile. … Canadians would benefit from reducing consumption of ultra-processed foods and beverages and increasing consumption of freshly prepared dishes made from unprocessed or minimally processed foods.”

A cross-sectional analysis that included more than 7,400 Australian adults found a “significant” link between the consumption of ultra-processed foods and obesity risk, even after adjusting for lifestyle and socio-demographic factors. Further, the study authors wrote: “Those in the highest quintile of ultra-processed food consumption had significantly higher BMI and waist circumference and higher odds of having obesity and abdominal obesity compared with those in the lowest quintile of consumption.” These associations were observed “in all age groups, sex and physical activity level.” The research, which was published in 2020 in the journal Nutrition & Diabetes, concluded “The findings add to the growing evidence that ultra-processed food consumption is associated with obesity and support the potential role of ultra-processed foods in contributing to obesity in Australia.”

Published in the British Journal of Nutrition, research published in 2018 examined the data of more than 15,000 U.S. adults. Consuming a high amount of ultra-processed foods was associated with higher body mass index and greater waist circumference and higher risk of obesity, and that link is even more notable in women. The study authors wrote: “Our findings suggest that ultra-processed foods may contribute to the high rates of excess weight and abdominal obesity in the USA. This study makes an important contribution to the literature as the first study to investigate this association in a US setting, confirming findings from Brazil, France and Spain. Given the unprecedented rates of obesity worldwide, it is crucial to further elucidate the role of ultra-processed foods in the development of excess weight and adiposity.”

Books:

Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease, by Dr. Robert H. Lustig, 2013

Journalism and opinion:

Bernie Sanders: We can’t allow the food and beverage industry to destroy our kids’ health, by Sen. Bernie Sanders, USA Today, Dec. 14, 2023

Why Eating Processed Foods Might Make You Fat, by Anahad O’Connor, New York Times, May 16, 2019

Can Home Cooking Reverse the Obesity Epidemic? by Anahad O’Connor, New York Times, June 12, 2019

Whose fault is obesity? Most of the blame rests with one culprit, by Tamar Haspel, Washington Post, June 29, 2023

Why are Americans so sick? Researchers point to middle grocery aisles, by Anna Lamb, Harvard Gazette, Dec. 19, 2023

Label ultra-processed foods ‘addictive’ to tackle obesity, say scientists, by Eleanor Hayward, The Times, Oct. 10, 2023

Q&A: Overfed and undernourished — the global issue of obesity and malnutrition, by Ryan O’Hare, Imperial College of London, Feb. 16, 2022

Processed food and sugar have become so widespread that obesity and malnutrition are now inseparable, Hilary Brueck, Business Insider, Dec. 15, 2019

We are producing a series that reports on the science behind the health risks of ultra-processed foods (UPFs). Learn more about the risks at our other fact sheets on all-cause mortality and cancer, along with our fact sheet that offers a general overview of UPFs here. These fact sheets are works in progress and will be updated. Please feel free to email mikaela@usrtk.org with any research or articles that you feel should be included in this series.

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