Written by the Nuvirox Research Team
Key points
- In a controlled inpatient trial, 20 adults ate about 508 more calories a day on an ultra-processed menu than on an unprocessed one matched for calories, sugar, fat, sodium and fiber.
- Participants gained roughly 0.9 kg on the processed diet and lost roughly 0.9 kg on the unprocessed one, over two weeks each.
- The trial establishes an effect on intake and weight. It did not measure fatigue directly, so claims that processed food causes tiredness remain an inference rather than a finding.
Short answer: the intake effect is well demonstrated; the tiredness link is plausible but not directly proven. The cleanest experiment anyone has run on this question locked 20 people on a metabolic ward and fed them two diets matched nutrient for nutrient. On the ultra-processed menu they spontaneously ate about 500 extra calories a day and gained weight. That is a genuine causal finding about eating behaviour. Whether the same foods directly cause fatigue is a separate question the trial was not designed to answer.
A note on how to read this. This article discusses a study about food processing and appetite. It is not a diet plan, and it deliberately contains no calorie targets, meal prescriptions or restriction advice. If you find that reading about food, weight or calories tends to make eating harder rather than easier for you, this is a reasonable article to skip. If your relationship with food feels distressing or out of your control, the National Alliance for Eating Disorders helpline can point you toward support.
Design and headline result of the NIH inpatient crossover trial. Both menus were matched on presented calories, energy density, macronutrients, sugar, sodium and fiber.
What does ‘ultra-processed’ actually mean?
It refers to a classification system based on the extent and purpose of industrial processing, not on nutrient content. The NOVA framework, which the research literature largely uses, places foods in four groups: unprocessed or minimally processed, culinary ingredients, processed foods, and ultra-processed formulations.
The fourth group is characterised by industrial formulations typically containing substances not used in home cooking — protein isolates, modified starches, emulsifiers, colourings, flavourings and non-sugar sweeteners — assembled into ready-to-eat products. Crucially, the classification is about how a food was made, not how much fat or sugar it contains. That distinction is exactly what made a controlled test possible.
What human studies actually show
The trial design was unusually rigorous for a nutrition study. Twenty weight-stable adults, mean age 31, average BMI 27, were admitted to the NIH Clinical Center and randomised to two weeks of an ultra-processed diet followed by two weeks of an unprocessed diet, or the reverse order. Meals were matched for presented calories, energy density, macronutrients, sugar, sodium and fiber. Participants were told to eat as much or as little as they wanted, and food was provided at roughly twice estimated maintenance needs so intake was never constrained.
The intake difference was large and consistent. Energy intake was 508 kcal per day higher on the ultra-processed diet. The extra calories came from carbohydrate (280 kcal/day) and fat (230 kcal/day), with essentially no difference in protein intake. Weight change tracked intake closely, and participants gained about 0.9 kg on the processed diet and lost about 0.9 kg on the unprocessed one.
Eating rate emerged as a plausible mechanism. Participants ate the ultra-processed meals faster. Softer textures, lower chewing requirements and higher energy density mean more calories arrive before the satiety signalling that follows a meal has time to register. That is a mechanical explanation rather than a mystical one, and it does not require any particular additive to be villainous.
The honest counterweight: 20 people, four weeks, and vigorous published dissent. The same issue of the journal carried commentaries arguing the study was over-extrapolated. One pointed out the pitfalls of drawing population conclusions from short trials. Another argued the meaningful variable was freshly prepared meals rather than the ultra-processed category as such. Twenty participants is small even for a crossover design, and a four-week study cannot tell you what happens over years. The trial itself also noted an unexpected energy-balance discrepancy during the unprocessed phase that the authors could not fully explain.
Study snapshot
| Design | Randomised crossover, inpatient, ad libitum intake |
| Participants | 20 weight-stable adults (10 male, 10 female) |
| Duration | 2 weeks per diet, 4 weeks total |
| Key finding | +508 kcal/day and +0.9 kg on the ultra-processed diet |
| Published | Cell Metabolism, 2019 |
So where does the tiredness come in?
Indirectly, through mechanisms the trial did not measure. This is the part worth being honest about: the study measured intake, weight, body composition and metabolic markers. It did not administer fatigue questionnaires. Anyone telling you this trial proved processed food makes you tired is describing a study that was not run.
What can be said is that the proposed routes are individually plausible. Rapidly absorbed carbohydrate produces steeper glucose excursions and steeper falls afterward, which is the conventional explanation for the post-lunch slump discussed in why the afternoon crash happens. Diets built largely on ultra-processed products tend to displace foods carrying micronutrients relevant to energy metabolism. And chronic excess intake and weight gain independently associate with daytime sleepiness and disturbed sleep. Each link is defensible. The chain has not been tested end to end.
What this study won’t justify
It will not justify treating ‘processed’ as a moral category or eliminating whole food groups. The classification lumps together shelf-stable bread, protein bars, flavoured yoghurt and confectionery. Treating those as nutritionally equivalent because they share a NOVA group is not what the data supports, and it is the substance of the published objection.
It also will not explain fatigue that has a medical cause. If you are persistently tired, the list of testable explanations — thyroid function, iron status, B12, sleep-disordered breathing, depression, medication effects — deserves attention before your grocery list does. Our broader piece on what actually causes brain fog works through that differential. Reorganising your diet is a reasonable thing to do; using it as a substitute for a blood panel is not.
What follows practically?
The lever the trial identified is texture and eating rate, not any individual ingredient. Foods that require chewing, that arrive as recognisable components rather than assembled formulations, and that take longer to eat appear to result in eating less without any deliberate restriction. That is a substitution strategy rather than a subtraction one.
It also reframes the willpower story usefully. The participants in that ward were not weak; they were unaware. A 500-calorie daily gap emerged with no one noticing and no one trying. The honest implication is that the environment did most of the work, which is a more useful thing to change than your resolve. For a related look at how food-derived compounds get oversold as metabolic solutions, see our piece on green tea extract, and for the broader question of what is actually driving midlife weight change, whether metabolism slows with age.
Frequently asked questions
Is all processed food bad?
No, and the classification does not claim that. Freezing, pasteurising, canning and fermenting are all processing. The trial contrasted a specific category of industrial formulation against minimally processed foods; it did not test every food that has ever been processed.
Was it the additives?
The trial could not isolate that. Eating rate and energy density are the leading candidate mechanisms and require no additive to be harmful. Anyone naming a specific emulsifier as the culprit based on this study is going beyond what it measured.
Did people know which diet they were on?
The meals were obviously different, so blinding was impossible. What was blinded was the hypothesis — participants were not told which diet was expected to produce which effect, and food intake was measured rather than self-reported.
Does this mean I’ll lose weight by cutting processed food?
The trial showed weight loss during the unprocessed phase over two weeks, in a controlled ward, with all meals prepared. That is not the same as a prediction for ordinary life, and the study says nothing about durability over months or years.
Why does processed food seem to make me crash?
The most likely explanation is a combination of rapid glucose absorption and the volume of food eaten quickly, though the crash experience is also strongly influenced by sleep, meal timing and circadian factors that have nothing to do with processing.
From Nuvirox
Why we formulated NAD+ Restore
No supplement corrects a food environment, and we would rather say that than imply otherwise. What a supplement can reasonably address is the cofactor side of cellular energy metabolism — which is why we built around an ingredient with published human trial data instead of a proprietary blend.
- 500 mg Nicotinamide Riboside Chloride (NR) — one of the two most-researched NAD+ precursors, within the dose range used in published human trials.
- 150 mg trans-resveratrol (Japanese Knotweed) and 50 mg quercetin (Sophora japonica) — polyphenols studied alongside NAD+ pathways for cellular health support.
- 10 mg galactomannans from fenugreek — to support absorption.
- 60-day money-back guarantee — long enough to actually evaluate it the way the research says you should.
The bottom line
The NIH trial is the strongest causal evidence in this area and it establishes something narrower than the headlines suggest: matched for nutrients, an ultra-processed menu led people to eat about 500 more calories a day without noticing. Weight followed intake. The fatigue link is a reasonable inference built from separate mechanisms rather than a measured outcome, and it deserves to be described that way. The practically useful finding is not that processed food is toxic — it is that food texture and eating rate influence how much you eat, entirely outside your awareness.
References
- 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 Metabolism. 2019;30(1):67–77.e3. PMID: 31105044. DOI: 10.1016/j.cmet.2019.05.008.
- Ludwig DS, Astrup A, Bazzano LA, et al. Ultra-processed food and obesity: the pitfalls of extrapolation from short studies. Cell Metabolism. 2019;30(1):3–4.
- Monteiro CA, Cannon G, Moubarac JC, Levy RB, Louzada MLC, Jaime PC. Freshly prepared meals and not ultra-processed foods. Cell Metabolism. 2019;30(1):5–6.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.