Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of Ad Libitum food intake

Summary

This inpatient randomised controlled trial demonstrated that ad libitum consumption of ultra-processed foods resulted in 508 kcal/day greater energy intake compared to matched unprocessed diets, driven by increased carbohydrate and fat consumption. Participants gained 0.8 kg during the ultra-processed diet phase and lost 1.1 kg during the unprocessed diet phase, with weight changes strongly correlated with energy intake (r=0.8). The findings suggest that ultra-processed food formulation—independent of macronutrient or basic nutrient composition—promotes overconsumption and may be a tractable target for obesity prevention.

Regional applicability

Whilst conducted in the United States, the mechanistic findings regarding ultra-processed food design and energy intake regulation are likely applicable to United Kingdom consumers, as ultra-processed foods share similar formulations across Western markets. UK policy and public health guidance on food processing and obesity prevention could draw on this evidence base.

Key measures

Daily energy intake (kcal/d), macronutrient intake (carbohydrate, fat, protein in kcal/d), body weight change (kg), correlation between energy intake and weight change (r)

Outcomes reported

The study measured ad libitum energy intake, macronutrient consumption, and body weight changes when 20 weight-stable adults consumed either ultra-processed or unprocessed diets for 2-week periods in a controlled inpatient setting. Meals were matched for presented calories, energy density, macronutrients, sugar, sodium, and fibre.

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