Ultra-Processed foods delay satiety, increase food intake and weight gain

Eating highly processed foods could be associated with weight gain finds a new study. The study was published in the latest issue of Cell Metabolism and is titled, “Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake.”

In the United States at present around 40 percent adults are obese says the 2015–2016 figures from the Centers for Disease Control and Prevention (CDC). The weight gain not only leads to problems such as heart disease, diabetes, stroke and kidney disease but also cancers. Multiple studies have shown the rise of obesity epidemic parallel to promotion and meteoric rise of processed and ultraprocessed foods. In fact ultraprocessed foods make up 58 percent of energy consumed.

Selection of frozen, processed, ready made food. Image Credit: Yolanta / Shutterstock
Selection of frozen, processed, ready made food. Image Credit: Yolanta / Shutterstock

Researchers defined ultraprocessed foods as canned or pre-prepared or frozen ready-to-cook dishes or packaged snacks etc. They write that these food items often contain high amounts of additives such as colours and flavours and are also rich in trans fats, salts, processed carbohydrates and sugars. These additives and artificial colours are often added to increase the palatability of these foods. The authors explain that sometimes different flavours and ingredients such as corn, wheat and soy are mixed in various proportions to make them more lucrative. On the other hand whole foods are eaten as they are originally present in nature with minimal changes.

The team writes that earlier studies have revealed that people eating more ultraprocessed foods are at a greater risk of cancers and obesity. This could be due to the ingredients in these foods. To explore this as a fact this team led by physiologist Kevin Hall from of the National Institute of Diabetes and Digestive and Kidney Diseases, and colleagues conducted an experiment including 10 men and 10 women who lived on-site at the National Institute of Health’s campus in Bethesda, Md. For four weeks. The participants were provided either a diet of whole foods for two weeks or a diet comprising of ultraprocessed foods for two weeks. For the next two weeks the diets were alternated. Both types of meals offered same numbers of calories, sugar, fat, fibre and other nutrients for the participants. Participants were given the choice to eat as much as they wanted in one hour time. For each of the participants, snacks were provided all day. These were appropriate for the type of diet the participant was on. Along with this meals were provided twice a day.

Dr. Hall in a statement said, “I was skeptical that we would see any difference in how many calories people ate, which was the primary interest of our study.” He went on to say that they did observe differences in the outcome of both types of diets. They npted that when allowed to eat as much as they could, people on the ultraprocessed diet are an average of 500 calories more per day compared to themselves when they were on whole foods. As a result when they were on the processed food diet, they gained around two pounds or an average of a kilogram in the two weeks of processed diets. Hall explained that this brings us to the question of what causes people to over eat and it was not just the sugar or the fats in these diets that was causing the weight gain. They explain that those on ultraprocessed diets eat more quickly and consume more. This speed, they speculate, alters the molecular signals that are generated in the body that tell a person to stop eating. “When people were consuming the unprocessed diet, the levels of a hormone called PYY, which is an appetite suppressant hormone secreted by the gut, actually increased. And similarly, another hormone that’s known to induce hunger, called ghrelin, deceased on the unprocessed diet,” Hall said.

The authors of the paper also wrote that weekly costs of ingredients to prepare 2,000 kcal/day of ultra-processed meals was around $106 compared to $151 for whole meals. They calculated the prices from ingredients sold at a local branch of a large supermarket chain.

The authors of the study wrote that nine participants are up to 1,500 kilocalories per day more when they were on ultraprocessed diet compared to when they were on whole diets. In total 11 people gained more weight while on ultraprocessed foods compared to when they were on whole foods. This weight gain was as high as six kilogrammes in two weeks they wrote. Some of the participants however did not show weight gain even when on ultraprocessed diets they wrote. Hall said, “We don’t know what drove those differences,” adding that these changes were irrespective of age and gender. He also said that there may be differences if diabetics and people with heart disease were included in the study.

Expert speak

Dr. David Ludwig, a pediatric endocrinologist at Boston Children’s Hospital was not associated with this study. He said that this study was in an artificial setting which can affect eating behaviour in many ways, “There’s social isolation, stress, boredom and the fact that the foods are prepared in a laboratory,” he explained. While these types of studies “are interesting and helpful, they’re not the whole story,” he said. He said, “There are potentially thousands of different nutrients and factors in food that could influence our biology or our senses as we eat. Those can interact in unpredictable and complicated ways.”

Barry Popkin, a nutrition professor at the University of North Carolina is another expert who has studied the effects of processed foods on weight gain. He was also not associated with this study. Popkin said in a statement, “The difference in weight gain for one [group] and weight loss for the other during these two periods is phenomenal. We haven't seen anything like this.” He concluded, “We should try to eat as much real food as we can. That can be plant food. It can be animal food. It can be [unprocessed] beef, pork, chicken, fish or vegetables and fruits. And one has to be very careful once one begins to go into other kinds of food.”

Dariush Mozaffarian, dean of Tufts University's Friedman School of Nutrition Science and Policy lauded the efforst of the team to match the two types of diet in temrs of calories, sugar, salt, protein, carbohydrates and fibres. Mozaffarian in a statemtn said, “These are landmark findings that the processing of the foods makes a huge difference in how much a person eats.” He added that “Putting people in a controlled setting and giving them their food lets you really understand biologically what's going on, and the differences are striking.”

Elisabetta Politi of the Duke Diet and Fitness Center in Durham, North Carolina, in her statement said, “Satiety is higher and longer lasting when we eat foods that have been minimally processed.”

Dr Gunter Kuhnle, from the University of Reading said that most of the ultraprocessed foods are so processed to increase their, “palatability, safety and preservation”. He said, “This is a well designed and well conducted study with interesting, although perhaps not surprising, outcomes. It seems that participants found ultra-processed food more palatable, ate more quickly and consequently more - possibly because it took longer for them to feel full.” He concluded, “A very interesting outcome of the study is the cost-per-energy: the ultra-processed diet was considerably cheaper than the unprocessed control diet, and this is likely to have implications from a public health point of view.”

Dr. Rekha Kumar, an endocrinologist and an assistant professor of medicine at NewYork-Presbyterian and Weill Cornell Medicine in New York City also called this a “great study” saying, “Even though the obesity epidemic was correlated with the increasing prevalence of processed food consumption, this is the first time we’ve seeing this in a randomized, controlled trial. This kind of study is hard to do. I have a feeling that other things, such as blood sugar and liver enzymes, would go the wrong way as well with these ultra-processed foods in a longer-term study.”

Is high consumption of ultraprocessed food associated with an increase in overall mortality risk?

A couple of months back in February this year a team of researchers led by Laure Schnabel, published a study showing that eating ultraprocessed foods could shorten the life span. The team published their findings in the JAMA Internal Medicine. The study was titled, “Association Between Ultraprocessed Food Consumption and Risk of Mortality Among Middle-aged Adults in France.”

The study included 44,551 French adults aged 45 and older. Their diet was assessed over a period of two years and around 15 percent of their diets were from ultra-processed foods. Following up the participants for up to nine years they noted that high intake of ultra processed foods led to higher risk of early death due to all causes. More important causes of deaths were heart disease and cancers among these patients, they noted. The authors explain that the risks of these diseases could be due to the excess salt and sugars and fats in these diets.

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. Charles Rader Charles Rader United States says:

    The use of the term "processed" is logically silly. If the people who process a food change it by adding or omitting ingredients that cause an undesired side effect, it is those ingredients, not the general fact of processing, that are the problem. For example, a processed food with added salt may have the undesired side effect of hypertension. A food processed in exactly the same way but without added salt would not affect hypertension. There is no clear meaning about what "processed" means since there is a huge variation in how foods are "processed".

    Take the age old method of food preservation by drying.  I suppose nobody would call that ultra-processed. But what about freeze drying?

    In at least some cases the purpose behind a processing technique is to prevent a possible undesired effect. Pasteurization is a case in point. There is a small but vocal group who campaign against pasteurization, regardless of actual data, and they will surely take encouragement from this story about "ultra-processed foods".

    In a similar way, the use of preservatives should not be collected into a single category. Obviously each preservative is different and some may have undesirable side effects which others don't. But the side effect of NOT using a preservative may be that the food is slightly spoiled and dangerous to eat.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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