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Ultra-Processed Diet Leads to Extra Calories, Weight Gain

Posted on by Dr. Francis Collins

Dietary Weight Gain and Loss
Credit: Hall et al., Cell Metabolism, 2019

If you’ve ever tried to lose a few pounds or just stay at a healthy weight, you’ve likely encountered a dizzying array of diets, each with passionate proponents: low carb, low fat, keto, paleo, vegan, Mediterranean, and so on. Yet most nutrition experts agree on one thing: it’s best to steer clear of ultra-processed foods. Now, there’s some solid scientific evidence to back up that advice.

In the first randomized, controlled study to compare the effects of ultra-processed with unprocessed foods, NIH researchers found healthy adults gained about a pound per week when they were given a daily diet high in ultra-processed foods, which often contain ingredients such as hydrogenated fats, high fructose corn syrup, flavoring agents, emulsifiers, and preservatives. In contrast, when those same people ate unprocessed whole foods, they lost weight.

Intriguingly, the weight differences on the two diets occurred even though both kinds of foods had been carefully matched from a nutritional standpoint, including calorie density, fiber, fat, sugar, and salt. For example, breakfast for the ultra-processed group might consist of a bagel with cream cheese and turkey bacon, while the unprocessed group might be offered oatmeal with bananas, walnuts, and skim milk.

The explanation for the differences appears to lie in the fact that study participants were free to eat as little or as much food as they wished at mealtimes and to snack between meals. It turns out that when folks were on the ultra-processed diet they ate significantly more—about 500 extra calories per day on average—than when they were on the unprocessed diet. And, as you probably know, more calories without more exercise usually leads to more weight!

This might not seem new to you. After all, it has been tempting for some time to suggest a connection between the rise of packaged, ultra-processed foods and America’s growing waistlines. But as plausible as it might seem that such foods may encourage overeating, perhaps because of their high salt, sugar, and fat content, correlation is not causation and controlled studies of what people actually eat are tough to do. As a result, definitive evidence directly tying ultra-processed foods to weight gain has been lacking.

To explore the possible connection in the study now reported in Cell Metabolism, researchers at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases took advantage of the Metabolic Clinical Research Unit at the NIH Clinical Center, Bethesda, MD. The unit is specially equipped to study issues involving diet and metabolism.

The researchers asked 20 healthy men and women of stable weight to stay at the center for 28 days. Each volunteer was randomly assigned to eat either an ultra-processed or unprocessed diet for two consecutive weeks. At that point, they switched to the other diet for another two weeks.

Both diets consisted of three daily meals, and volunteers were given permission to eat as much food as they liked. Importantly, a team of dieticians had carefully designed the ultra-processed and unprocessed meals such that they were well matched for total calories, calorie density, macronutrients, fiber, sugars, and salt.

At lunch, for example, one of the study’s processed meals consisted of quesadillas, refried beans, and diet lemonade. An unprocessed lunch consisted of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds with a side of grapes.

The main difference between each diet was the proportion of calories derived from ultra-processed versus unprocessed foods as defined by the NOVA diet classification system. This system categorizes food based on the nature, extent, and purpose of food processing, rather than its nutrient content.

Each week, researchers measured the energy expenditure, weight, and changes in body composition of all volunteers. After two weeks on the ultra-processed diet, volunteers gained about two pounds on average. That’s compared to a loss of about two pounds for those on the unprocessed diet.

Metabolic testing showed that people expended more energy on the ultra-processed diet. However, that wasn’t enough to offset the increased consumption of calories. As a result, participants gained pounds and body fat. The study does have some limitations, such as slight differences in the protein content of the two diets. and the researchers plan to address such issues in their future work.

During this relatively brief study, the researchers did not observe other telltale changes associated with poor metabolic health, such as a rise in blood glucose levels or fat in the liver. While a couple of pounds might not sound like much, the extra calories and weight associated with an ultra-processed diet would, over time, add up.

So, it appears that a good place to start in reaching or maintaining a healthy weight is to follow the advice shared by all those otherwise conflicting diet plans: work to eliminate or at least reduce ultra-processed foods in your diet in favor of a balanced variety of unprocessed, nutrient-packed foods.


[1] Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Hall KD et al. Cell Metab. 2019 May 16.


Obesity (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)

Healthy Eating Plan (National Heart, Lung, and Blood Institute/NIH)

Body Weight Planner (NIDDK/NIH)

Kevin D. Hall (NIDDK/NIH)

Metabolic Clinical Research Unit (NIDDK/NIH)

NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases


  • Bruce Vaughn says:

    If you had included a link to a listing of high processed foods that would have been helpful.

  • Judith Miller says:

    I need to know what are the highly processed foods. I would not think the tortilla for the quesadilla and refried beans would be processed.. What is a definition of “processed?”

  • Charles Carter says:

    You are writing more as a promoter than scientist. Claims made about this study vastly over-reach. An NIH director should know better than to sensationalize science! The study shows convincingly that diets of very different compositions can lead to short term weight change. Comparators do NOT allow sole implication of processing.
    It would be wonderful if sustained weight loss were so simple, yet no RCT to date has shown meaningful sustained weight loss for any particular diet.
    This really adds little or nothing except to support criticism of nutrition science as a whole and of overstated claims by scientists and the press.

  • Jeffrey Lerner says:

    I followed the links, beginning with the reference at the bottom of the blog post, and got to the actual diets. The unprocessed is definitely abstemious.

  • Chuck Selden says:

    I agree with Charles Carter. The paper and the press release and the Director’s Blog all make the highly processed food into a villain. I content that very tasty and soft-cooked food (like in good restaurants and good home cooking) is simply so good on the palate that the eater just enjoys it and keeps eating for the joy of it. I saw the study tried to take this into account by asking the subjects to rate each meal for appearance and palatability, but I don’t think the rating process reliably reported the subjects’ physiological experience. The press clip and the paper both cited some components of highly processed food (flavorings, emulsifiers, etc.) that might be triggers to overeating but so far has only set the stage for testing those components in an unbiased fashion. The experiment needs to be repeated using good food, well-prepared, minus any suspect additives found in highly processed food. When the dust settles, I believe we will be back to where we started: you want to eat more good food, eat less dull or harder to eat food, and the key to weight loss or gain will still be the balance of calories eaten vs. calories burned. There is no substitute for voluntary restraint and an active life-style. Gluttony and sloth are fattening.

    • Jeannine Fiddament RN says:

      You’re absolutely right that the only way to lose weight is less calories in than what’re burned. On the contrary, the person who voluntarily eats low calories when they are highly concentrated, is the exception.

      • Chuck Selden says:

        Yes, it is tough to eat just a little of something really good. One must be mindful of one’s overall health, not just follow what the stomach wants.

  • Mary-Jo Overwater, MMSc, MSc, RDN says:

    It’s been well documented that taste, cost, access to, convenience, nutrition are factors influencing what people eat, in general. The cost and access to, but primarily the taste of wholesome foods in the USA, in my opinion, has declined in the past 30+ years! I am an American living in Europe now, for 34 years, and every year I return, I have noticed it and it’s just getting worse. Compared to other countries (I’ve lived in Europe — NL, Belgium, Russia, Austria — and U.K., but travelled to Africa, Middle East as well as many other European countries) and the taste (including other attributes of taste, such as texture, aroma, and mouth feel) difference between similar foods in The USA and other countries is startling inferior. I understand the food safety issues have always been so well-controlled in the US and Americans have benefited from that vs. other countries, but even that seems to be slipping. It’s no wonder Americans choose ultra-processed over wholesome. In the study, I see that the subjects enjoyed the unprocessed diet, but, perhaps, that’s because it was conveniently prepared for them. In general, I believe the USA really has to take a hard look at its food growing and distribution systems in order to assure that wholesome foods are as tasty, accessible, affordable, and convenient as ultraprocessed in order to shift consumption habits so as to decrease caloric intakes. All the nutrition facts labels in the world are not going to make Americans choose wholesome foods, habitually, in order to effect in consumption of diets that help decrease, better yet, prevent NCDs. This was a great study from the NIH to kick start some real action on this crucial reality. Thank you and keep at it!

  • Carl says:

    I think that common sense tells us that ultra-processed foods are bad, but it’s great to have a study back it up because some people just don’t want to see. So thank you for this! I believe people in America don’t worry enough for their health, and we need more consciousness about the risks of unhealthy diets. If you can, I recommend going to a doctor and having a specialized medical nutritional program. … Wake up, America! Your health is the most importatnt thing you will have in your life. More than riches, more than comfort. We need to discover the benefits of diet and exercise and how they can lead you to a longer, better life. It’s not a matter of looking good! It’s a matter of wellness and life.

  • Luz Alderete says:

    I loved what you shared, especially about Processed Diet Leads to Extra Calories, Weight Gain. I’m going to combine it with what I’m doing …

  • Rachel Green says:

    processed food not only increase your weight it would also increase the chance of diabetes and heart attack. We all should try to eat healthy and avoid these type of food as much as we can.

  • BDWP says:

    I recommend in this for all.

  • Ubong S says:

    Even most of the people these days are worried about obesity and weight gain. If you are also one of them, it is important to make some serious changes in your eating habits and workout routines.

  • I. says:

    I cherished what you shared, particularly about Processed Diet Leads to Extra Calories, Weight Gain. I’m going to join it with what I’m doing … – I just began my adventure a couple of days back and your story is exceptionally rousing and moving.

  • BIC says:

    Thanks for sharing this …

  • Michaela says:

    This makes so much sense! Thanks! Do you have any advice on how to help stop your cravings??? Any help would be great! Thanks! 🙂

  • Krel says:

    Thanks for this article. It is interesting.

  • David says:

    Hi, Nice article . . .

  • Ema Hill says:

    but I don’t think the rating process reliably reported the subjects’ physiological experience. The press clip and the paper both cited some components of highly processed food (flavorings, emulsifiers, etc.) that might be triggers to overeating but so far has only set the stage for testing those components in an unbiased fashion

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