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by Dr. Chad Kerksick PhD January 10, 2023 6 min read

Education Objectives:

  • Calorie (energy) balance and how it impacts weight loss and fitness goals.
  • How diet quality can impact how much food we eat and how it impacts our body mass and body composition.

Processed Foods and Weight Gain

Does eating a diet high in processed foods really matter in terms of health, weight loss, and so forth? Sure, they aren’t as nutritious, lack fiber, and have other less than favorable outcomes, but they taste so good! Plus, many people are busy and like foods that are quick and easy. Does eating more of highly processed foods actually impact weight gain or weight loss?

A study completed by researchers who worked for the National Institutes of Health examined the question, “Does Eating a Diet High in Processed Foods Impact How Much Weight You Gain or Lose?

Why is This Study Important or Who Cares?

For health nuts out there it is bad news to first highlight that the majority of calories consumed in the United States come from ultra-processed foods.

Why is this? Several reasons. First, they are relatively inexpensive. Second, they can sit on shelves for long periods of time and are largely safe from pathogen growth in the food. Third, they can provide key nutrients (due to fortification programs). Fourth, they oftentimes have added sugars, sodium, texture agents, etc. to make them taste good. Finally, they are convenient.

In terms of weight loss, however, ultra-processed foods may promote overeating due to them being high in salt and sugars while also possessing unique characteristics that disrupt signaling between your stomach and brain, resulting in overeating.

If you add all of these things together, one can see why having a better understanding of the true impact of eating a diet high in ultra-processed foods on weight loss and fat gain is important. People who are overweight and develop obesity oftentimes have low fitness capacities, poor metabolic health, and are more likely to develop heart disease, diabetes, cancers, etc. and all of these lead to poor quality of life and added expenses upon our society due to the medical costs associated with medically treating these people.

  Ultra-Processed Unprocessed
Calories 3905 3871
Carbohydrates (%) 49.2 46.3
Fat (%) 34.7 35.0
Protein (%) 16.1 18.7
Sodium (mg/1000 kcal) 1997 1981
Fiber (g/1000 kcal) 21.3 20.7
Sugars (g/1000 kcal) 34.5 32.7
Energy from Unprocessed (%) 6.4 83.3
Energy from Ultra-processed (%) 83.5 0


What Did They Do?

Remember, the researcher’s goal was to examine the role of eating a diet high in ultra-processed foods on changes in body weight, body composition, and other health markers. To complete this study, 10 healthy men and 10 healthy women completed a 28-day study where they were checked in to a research hospital. For two weeks they were given a diet containing non-processed foods and for two weeks they were given a diet high in ultra-processed foods (1). This is really important as this approach offers some of the best control over what the research participants were doing and what they were eating.

During each two-week phase, the people in the study were given three meals each day and were instructed to eat as much or as little as they wished, and each meal was available to them for 60 minutes. A rotation of meals was provided to offer variety and to mimic real-world eating conditions. As best as they could, meals were matched for total calories, macronutrients, fiber, sugars, and sodium, but varied greatly in the percentage of foods provided from either unprocessed or ultra-processed foods. The small table below highlights the calories, macronutrients, sodium, sugars and percentage of foods from ultra-processed and unprocessed foods.

In addition, snacks were given that were appropriate to each diet including bottled water. Both meal plans were designed to provide twice (2x) the total daily calories in an amount that exceeded their amount of calories needed for weight maintenance.

What Did They Find?

Several key things were identified as part of this study that can help people better understand how eating a diet high in ultra-processed foods can impact calorie intake and body mass. Below is a table that summarizes the results.

Appetite Control

Appetite control was better when eating unprocessed foods and appetite control is quite poor during the first few days of being presented with processed foods. Calorie intake during the unprocessed diet did not change across the two-week study period, but calorie intake during the ultra-processed decreased significantly across the two-week period.

Calorie Intake

As seen in the graph on the right, energy intake during the high processed diet was 459 ± 105 kcals/day higher than eating a diet high in unprocessed foods.

Macronutrient Intake

As seen in the graph on the right, when consuming the ultra-processed diet, participants ate more carbohydrates (280 ± 54 kcals/day) and fat (230 ± 53 kcals/day) when they consumed the unprocessed diet.

Calorie Intake At Each Meal

As seen in the graph on the right, participants ate approximately 144 more calories during breakfast, 248 more calories during lunch, and 108 more calories during dinner when eating the diet with ultra-processed foods when compared to what they ate with unprocessed foods.

Body Weight Changes

The most meaningful outcomes are that participants who consumed the ultra-processed diet gained approximately 0.9 kilograms (about 2 pounds) when eating the ultra-processed diet while people consumed the diet with unprocessed foods lost about the same amount of weight (two pounds). As expected, the primary explanation for the body mass change was the differences in how many calories were consumed.

Head to Head Comparison of Diet Changes

  Ultra-Processed Unprocessed
Appetite Control Worse Better
Daily Calories Higher Lower
Daily Carbohydrate Intake
Higher
Lower
Daily Protein Intake
Higher
Lower
Daily Fat Intake Similar
Similar
Breakfast Calories
Higher
Lower
Lunch Calories
Higher
Lower
Dinner Calories
Higher
Lower
Snack Calories
Similar
Similar
Body Weight Gained Lost
Fat Mass
Gained
Lost


Body Composition Changes

In agreement with the changes observed in body weight, when participants consumed the ultra-processed diet, a significant increase in body fat occurred while body fat levels decreased when consuming the diet focused on unprocessed foods.

Take Home

Does this study relate to you? It likely does as this study has tremendous implications for any person desiring to lose fat or any person who is working with or helping people who want to lose fat. When you consider that over 60% of the American public is overweight, one-third of American adults are classified as obese, and the rates of cardiovascular disease, diabetes, and other metabolic problems increase as people age and all of these are related to obesity status, the results impact many people.

Also, how many people do you know who eat a diet that contains too much processed foods and they generally don’t eat foods that aren’t packaged or prepared ahead of time. The results from this study clear show in a relatively short period of time that eating a diet like this makes it very hard for people to know and/or manage how many calories they consume. This inability to regulate food intake leads to a significant increase in body mass and body fat in just one week.

Where To From Here?

It’s easy for someone to recommend that a person stops eating processed foods altogether and while that would help someone better control their energy intake and manage their health and weight, this may or may not be realistic. So my recommendation would be for people to reflect and absorb what this study tells us, and from there, consider how their grocery shopping habits can change. Yes, more time will likely need to be invested to find recipes to make versus eating something pre-packaged. The other recommendation would be for people to try to develop a greater sense of awareness with how much they are eating. We oftentimes have no ability to control what foods are available at a party, on a road trip, in the airport, etc. and taking information from this study could help motivate people to choose foods that are less processed. Small changes and ongoing commitment should allow for dietary habits to evolve and ideally become healthier.

About the Author

Chad Kerksick is currently an Associate Professor of Exercise Science and Director of the Exercise and Performance Nutrition Laboratory at Lindenwood University. Dr. Kerksick earned his PhD in Exercise, Nutrition, and Preventive Health in 2006. Since that time has worked as a university professor teaching classes and conducting research in areas related to exercise and nutrition. His laboratory, the Exercise and Performance Nutrition Laboratory (www.lindenwood.edu/EPNL), conducts rigorous, high-quality research investigations devoted to examining the impact of exercise and nutritional interventions of health, performance, and recovery of a large number of populations. Chad has worked with 1st Phorm since 2010 providing educational content in multiple formats, assisting with educational events, and providing feedback for formulations and labeling.

References:

1. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell metabolism. 2019;30(1):67-77 e3.

Dr. Chad Kerksick PhD
Dr. Chad Kerksick PhD

PhD, Exercise, Nutrition, and Preventive Health NSCA Certified Strength and Conditioning Specialist (CSCS*D) NSCA Certified Personal Trainer (NSCA-CPT*D) ISSN Certified Sports Nutritionist (CISSN) Academic Fellow, American College of Sports Medicine (FACSM) Academic Fellow, National Strength and Conditioning Association (FNSCA), Academic Fellow, International Society of Sports Nutrition (FISSN)