How Ultra-Processed Foods Could Cause Disease: Calorie Density

Dr. Greger - May 2025

"The biological mechanisms our bodies use to regulate our weight likely evolved in the context of eating at least four or five pounds of food a day."

Transcript

One of the mechanisms linking increased consumption of ultra-processed foods and increased risk of death and disease is calorie overload, leading to excess body fat. This could be due to all the extra sugar and fat added to these foods, but in my last video, I profiled a randomized, controlled trial that found that those on the ultra-processed diet gained more weight than those eating unprocessed foods, even when the two diets were matched with the same nutrient profile.

But ultra-processed foods are also designed to be eaten quickly, and indeed, the ultra-processed group snarfed calories at a 50% faster rate. So, changes in texture due to processing may contribute to the calorie overload, but so too may the increased calorie density of ultra-processed foods, as well as the degradation of the food matrix.

Calorie density is the number of calories for a given weight or volume of food. Some foods have more calories per cup, per pound (0.45 kg), per mouthful than others. Oil, for example, has a high calorie density, which means it has a high calorie concentration with lots of calories packed into a small space. Drizzling just one tablespoon of oil on a dish adds 120 calories. For those same 120 calories, you could eat about two cups (300 g) of blackberries, a food with a low calorie density. You could swallow that spoonful of oil and not even feel a difference in your stomach, but eating a couple of cups of berries could start to fill you up.

A handful of jelly beans has about 16 times more calories than a handful of cherry tomatoes. So, for the same number of calories, you could eat that one handful of jelly beans or about four cups (600 g) of cherry tomatoes. A large serving of French fries is about the same size and weight as a baked potato but has about four times as many calories. So, for the same number of calories, you could have that single serving of fries or around four baked potatoes. Which do you think would be more filling?

Ultra-processed foods tend to have twice the calorie density compared to unprocessed foods, more than 1000 calories per pound, similar to what you see at fast food joints, whereas rural West African diets that closely represent the likely diet of our ancient ancestors, average fewer than 500 calories per pound.

So, the biological mechanisms our bodies use to regulate our weight likely evolved in the context of eating at least four or five pounds (1.80 to 2.25 kg) of food a day. That may be the more natural amount of food we eat. If your body is counting on eating five pounds (2.25 kg) of food but you max out with the same number of calories eating just two pounds (1 kg) of ultra-processed food, what do you think happens? It’s no wonder we overeat—our bodies are expecting three more pounds (1.35 kg) of food! Our bodies just weren’t designed to handle such calorie-concentrated diets. No wonder ultra-processed foods are more fattening.

But wait. That study where people ended up four pounds (1.8 kg) heavier within two weeks of eating an ultra-processed diet compared to an unprocessed diet, not only matched the two diets for nutrients like fat and sugar but also for calorie density. How did they do that?

Here’s an example of one of the ultra-processed meals the researchers fed people: a deli meat and cheese quesadilla with ultra-processed refried beans, sour cream, and salsa. Compare that to one of their unprocessed meals: a big Southwestern entrée salad with black beans, nuts, avocados, corn, grapes, apples. Wait a second! How could you possibly make these the same calorie density? The same number of calories per pound? By adding not one, not two, not three, not four, but five cups of Crystal Light—diet, sugar-free lemonade to help even out the calories per total poundage. But that’s kinda cheating. Calorie density shouldn’t be based on foods and beverages, but ideally based on food only, because beverages are so heavy just from the water that they can disproportionately inﬂuence calorie density calculations. If you just look at the calorie density of the food, the nonbeverage calorie density was 85% higher on the ultra-processed foods diet, which could account for some of that weight gain.

You can’t fault the researchers for trying the diet lemonade trick; high calorie density is such an inherent property of so many ultra-processed foods. How else could you possibly actually match it with a variety of unprocessed foods? And that’s the problem; high calorie density is one of the reasons ultra-processed foods may be contributing to obesity.

References

Astrup A, Monteiro CA. Does the concept of “ultra-processed foods” help inform dietary guidelines, beyond conventional classification systems? NO. Am J Clin Nutr. 2022;116(6):1482-1488.
Hall KD, Ayuketah A, Brychta R, et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metab. 2019;30(1):67-77.e3.
Gupta S, Hawk T, Aggarwal A, Drewnowski A. Characterizing ultra-processed foods by energy density, nutrient density, and cost. Front Nutr. 2019;6:70.
Prentice AM, Jebb SA. Fast foods, energy density and obesity: a possible mechanistic link. Obes Rev. 2003;4(4):187-194.
Ledikwe JH, Blanck HM, Khan LK, et al. Dietary energy density determined by eight calculation methods in a nationally representative United States population. J Nutr. 2005;135(2):273-278.
Forde CG, Mars M, de Graaf K. Ultra-processing or oral processing? A role for energy density and eating rate in moderating energy intake from processed foods. Curr Dev Nutr. 2020;4(3):nzaa019.

Question about adding bulk food to UPF diet (Volumetics)

Dr. Greger stated that humans used to consume about 6 lbs of food daily, and now that we eat ultraprocessed foods, we consume more calories. I wonder if a person consuming UPF were to add bulk - say carrots, if they might reduce obesity, or at least not gain more weight? Here is the page I made for his statement

Claude AI Answer

Your hypothesis is well-supported by ~25 years of randomized controlled trial work, and it's actually a natural companion to Greger's argument. The researcher to know here is Barbara Rolls at Penn State, whose "Volumetrics" research program has tested exactly this question repeatedly.

The core finding that validates your intuition

Rolls' work converges on a principle that's essentially the mirror image of Greger's: people generally eat a similar weight of food per day, so by choosing foods with lower caloric density, individuals can eat more food, feel full, and improve their nutrient intake while losing weight. This is the same volume-regulation mechanism Greger invokes — just applied prescriptively rather than diagnostically.

Three distinct "add bulk" strategies have been tested, with different effect sizes

Preloading — eating low-density food before the main meal. The classic finding: a large bowl of broth-based soup as a first course before lunch makes it easier to eat fewer calories for lunch, without compensatory eating at dinner. This is the strategy closest to your "add carrots" scenario — eat a couple of raw carrots 15 minutes before a meal.
Hidden vegetables — pureeing vegetables into existing dishes. Rolls' 2011 AJCN paper ("Hidden vegetables: an effective strategy to reduce energy intake and increase vegetable intake in adults") is the key citation. Incorporating pureed vegetables into bread, pasta sauce, and chicken noodle casserole reduced energy intake by 12%, and if you eat the same portion you always eat, you'll consume fewer calories. People don't appear to compensate by eating more later.
Reformulation — straightforward swaps. Using Volumetrics principles to reduce calories per bite by 30% and serving size by 25%, participants ate 800 calories less per day and never missed them.

The critical caveat for your specific framing

There's an important distinction between adding bulk on top of an unchanged UPF intake versus displacing UPF with bulk. Carrots aren't free calories — a pound of carrots is ~185 kcal. If someone keeps eating their full UPF load and adds a pound of carrots, they'd add ~185 kcal/day (potentially +19 lbs/year if no compensation occurs).

The whole mechanism depends on the bulk displacing UPF intake via the stretch/satiety signaling Greger describes. The good news: the RCT evidence consistently shows that when bulk is added strategically (preload, hidden, larger portions of low-density food on the plate), people do compensate downward on the calorie-dense items — they don't just stack calories.

Why carrots specifically are a reasonable choice but not optimal

Raw carrots have several useful properties: ~88% water, slow eating rate (lots of chewing), about 25 kcal per medium carrot, decent fiber, cheap, and shelf-stable. The slow oral processing matters — recall Forde, Mars & de Graaf 2020 (already on your reference list) on how eating rate independently moderates intake from processed foods.

But broth-based vegetable soups consistently outperform raw vegetables in preload trials, probably because the warm liquid volume amplifies the gastric distension signal. If you wanted to extend the page with a "what you can do about it" angle, the preload soup evidence is the most robust.

Where the evidence gets thinner

What hasn't been tested well, as far as I can find: a long-duration RCT specifically pairing low-density vegetable additions with a sustained UPF-dominant diet. Most Rolls trials are weeks-long and use mixed diets, not "UPF + carrots" specifically. The Hall 2019 NIH inpatient trial — already a centerpiece of your page — didn't have a "UPF + added vegetables" arm. So your hypothesis is mechanistically plausible and supported by adjacent RCT evidence, but the exact intervention (keep eating UPF, add bulk to displace some of it) hasn't been directly tested in the populations where it would matter most. That's actually a legitimate research gap worth flagging on the page.

How Ultra-Processed Foods Could Cause Disease: Calorie Density

Dr. Greger - May 2025

References

Question about adding bulk food to UPF diet (Volumetics)

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