Consumption, appetite and weight gain of ultra-processed foods

Relation

Hall KD, Ayuketah A, Brychta R, et al. Ultra-processed diets cause excessive calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake.Cell metabolism. 2019;30:1-11.

Draft

Randomized controlled trial

Objective

To determine the effects of a highly processed diet compared to an unprocessed diet on appetite and weight gain

Participant

The study included 20 adult inpatients (mean age 31.2) at the National Institutes of Health (NIH) Clinical Center; Participants had a stable weight and an average BMI of 27.

intervention

Participants had access to either a selection of highly processed foods or a selection of unprocessed foods and were instructed to eat freely (ad libitum) for 2 weeks. Meals were tailored for available calories, energy density, sugar, fiber, sodium and macronutrients. Each cohort crossed over to the other arm after 2 weeks. There was no washout period.

Target parameters

Calorie consumption and weight change were the primary outcome measures. Nutrient intake, appetite, energy expenditure, physical activity and energy balance were also tracked.

Key insights

During the 2 weeks on the ultra-processed food diet, caloric intake increased by approximately 500 calories per day (508 ± 106 kcal/day;P=0.0001). There was also an increased intake of carbohydrates (280 ± 54 kcal/day;P<0.0001) and fat (230 ± 53 kcal/day;P=0.0004); no significant changes in protein intake were observed (−2 ± 12 kcal/day;P=0.85).

Not surprisingly, weight changes were closely correlated with calorie intake. Participants gained weight (0.9 ± 0.3 kg;P= 0.009) on the ultra-processed food diet, and they lost weight (0.9 ± 0.3 kg;P=0.007) on the diet with unprocessed foods. These changes also occurred within 2 weeks of each diet.

Practice implications

We almost didn't want to cover this study because our first response was, "Of course eating processed foods caused weight gain!" This is likely the response from integrative practitioners worldwide who question the safety of ultra-processed foods. And yet it's hard to believe that this is truly the first randomized controlled trial to show that a highly processed diet is associated with weight gain.

Previous publications have pointed to the connection. A review by Poti et al. in 2017 found that “evidence” suggests a harmful link between consumption of ultra-processed foods and obesity.¹These researchers also identified an association between ultra-processed foods and an increased risk of metabolic syndrome, increased total and low-density lipoprotein (LDL) cholesterol, and the risk of high blood pressure.

This new randomized inpatient study confirms our existing understanding and long-standing belief about highly processed diets - that they may be a key factor in the growing obesity epidemic. Furthermore, once you really delve into the details of the study and the sophisticated manner in which it was conducted, there is so much to appreciate about this study.

Similar to the commentary we published in the June issue ofJournal of naturopathyregarding low-carbohydrate diet,²This study shows that the old adage “a calorie is a calorie” is an oversimplification.

A key aspect of this study was the researchers' ability to control dietary intake in both cohorts. The 2 diets contained approximately equal availability of carbohydrates, fats, and proteins. Additionally, the study mimicked real-world choices, with the ultra-processed choices containing foods that ordinary, moderately health-conscious Americans might eat every day.

For example, breakfast for the processed foods group might include a bagel with cream cheese and turkey sausage, while the unprocessed diet would be oatmeal with raw almonds, blueberries, and 2% milk.

An example of a processed lunch is a meat and cheese sandwich on white bread with diet soda and low-fat fries, while the unprocessed lunch consists of salmon, sweet potatoes and plain yogurt with strawberries.

So it's not like the processed diet included a daily dose of pepperoni pizzas, sugary sodas, chips, and donuts. The big difference from the processed menu was the ubiquity of so-called ultra-processed foods: breakfast cereals, muffins, chips, white bread, (seemingly virtuous) sugar-flavored yogurts, low-fat potato chips, fruit juices and diet drinks. That adds up to a plethora of artificial sweeteners, preservatives, emulsifiers, added sugars, flavor enhancers, sodium and unnatural oils.

This new randomized inpatient study confirms our existing understanding and long-standing belief about highly processed diets - that they may be a key factor in the growing obesity epidemic.

Another interesting finding from this study is the effect of ultra-processed foods on appetite. This study confirms that a highly processed diet increases appetite. This is likely due to boosting the hunger hormone ghrelin, while the unprocessed diet likely dampened ghrelin and increased the satiety hormone peptide tyrosine-tyrosine (PYY).^3.4Future studies with a similar design could use such laboratories to further describe the mechanism of increased calorie consumption in processed foods.

While this study is unique in many ways and specifically relates to weight gain, there have been other studies showing additional health effects of a highly processed diet. A prospective cohort by Filot et al. from 2018 showed a link between ultra-processed food intake and breast cancer and other cancers.⁵The researchers found that for every 10 percent increase in ultra-processed foods in the diet, there was a corresponding 12 percent increase in overall cancer risk and an 11 percent increased risk of breast cancer.

In their most recent 2019 observational prospective cohort study with nearly 45,000 participants, Schnabel et al. showed that an increase in consumption of ultra-processed foods was associated with an overall higher risk of all-cause mortality.⁶

Additionally, 2 large studies were published just last monthBMJfound a positive association between consumption of ultra-processed foods and the risk of cardiovascular disease and death. In the first study by Srour et al. More than 105,000 French adults were asked to fill out a questionnaire that identified 3,300 different foods and grouped them by level of processing. Similar to the breast cancer study, these researchers found that a 10 percent proportional increase in ultra-processed foods led to a 12 percent increase in overall cardiovascular disease, a 13 percent increase in heart disease, and an 11 percent increase in cerebrovascular disease.⁷

In the second study, Spanish university graduates with an average age of 38 years also received a nutritional questionnaire.⁸In this study, more than 4 servings of ultra-processed foods per day were associated with a whopping 62% increased risk of all-cause mortality compared to less than 2 servings per day. They also found that for each additional daily serving (over 4) of ultra-processed foods, the risk of mortality increased by 18%. In these two studies, researchers concluded that urgent action is needed to limit consumption of ultra-processed foods. We couldn't agree more.

The evidence is mounting and the case for limiting or avoiding ultra-processed foods is stronger than ever. Aside from contributing to our current obesity epidemic, evidence suggests that ultra-processed foods likely play a key role in a variety of chronic and fatal diseases, such as cancer and heart disease.