Ultra Processed Foods Cause Weight Gain

In a randomized controlled trial of 20 inpatient adults, subjects who consumed ultra-processed foods ate more and gained weight. According to the clinical report published May 16, 2019, “Subjects were admitted to the NIH Clinical Center and randomized to receive either ultra-processed or unprocessed diets for two weeks.” Then the subjects ate the alternate diet for the following two weeks. 

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The meals provided to both groups were equal in terms of “calories, energy density, macronutrients, sugar, sodium, and fiber.” Furthermore, subjects in the trial were “instructed to consume as much or as little as desired.” In other words, subjects were free to eat as much or as little as they wanted. 

The results showed adults on the ultra-processed diet ate more carbohydrates (280 +/- 54 calories/day) and fat (230 +/- 53 calories/day). However, adults on the unprocessed diet ate less and lost weight. Thus, the trial showed an ultra-processed diet caused weight gain, about 1 pound per week.

Ultra Processed Food Cause Weight Gain
Ultra-processed foods caused weight gain and unprocessed foods resulted in weight loss.

The trial results suggest “limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention and treatment.” So what are ultra-processed foods?

What are Ultra-Processed Foods?

The trial defined ultra-processed foods according to “NOVA classification.” NOVA classifies Ultra-processed food and drink products as “typically” having “five or more” ingredients and “usually many ingredients.” For example, substances only found in ultra-processed products include the following:

  • Hydrogenated oils
  • Hydrolyzed proteins
  • Soy protein isolate
  • Maltodextrin
  • High fructose corn syrup

Furthermore, ultra-processed products contain additives such as “non-sugar sweeteners,” also called artificial sweeteners, that promote metabolic syndrome and obesity. Examples of ultra-processed products include:

  • Carbonated drinks
  • Candies, chocolate, ice cream
  • Mass-produced packaged bread and buns
  • Cookies, pastries, and cakes
  • Breakfast cereals, energy bars, and drinks
  • Chicken and fish nuggets
  • Burgers, hot dogs, and sausages

Although the trial “attempted to match several nutritional parameters between diets, the ultra-processed versus unprocessed meals differed substantially in the following proportions:”

  • Ultra-processed meals had about 54% added sugar to total sugar compared to only 1% of unprocessed meals.
  • Ultra-process meals had only 17% insoluble to total fiber compared to 77% of unprocessed meals.
High Fructose Corn Syrup
High fructose corn syrup is an ultra-processed product.
Ultra-Processed carbonated drink
Carbonated drinks are an ultra-processed product.

In other words, ultra-processed foods have significantly more added sugars and less insoluble fiber than unprocessed foods. So what are unprocessed foods?

What are Unprocessed foods? 

The trial also defined unprocessed foods according to NOVA classification. NOVA classifies unprocessed foods as the following: 

  • Edible parts of plants (seeds, fruits, leaves, stems, roots)
  • Animals (muscle, eggs, milk)
  • Fungi (mushrooms), algae (seaweeds), and water 

Unprocessed food is minimally produced and may include the following processes to extend the food’s life:

  • Chilling, freezing, drying, and pasteurizing
  • Crushing or grinding seeds (seed butter)
  • Roasting coffee beans

It also includes the fermenting of milk to make yogurt. Examples of unprocessed foods:

  • Frozen or dried fruits such as apples and berries
  • Leafy and root vegetables (lettuce and carrots)
  • Legumes such as beans
  • Meat, poultry, fish, and seafood
  • Eggs and nuts
Unprocessed food bowel of berries
A bowel of fresh berries are unprocessed food.

So what are the conclusions of this clinical trial?


The 28-day trial showed adults who ate a diet of ultra-processed foods consumed more and gained weight. Conversely, adults who ate unprocessed food lost weight. Therefore, you can lose weight by avoiding ultra-processed foods and eating unprocessed foods.

Take the Processed Food Quiz

Answer the questions and submit quiz to view results.

How do ultra-processed foods affect your weight?An ultra-processed diet causes weight .
Which foods cause weight gain?
How do unprocessed foods affect your weight?An unprocessed diet causes weight .


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