Ultra-processed foods cause weight gain and increased energy intake associated with reduced chewing frequency: A randomized, open-label, crossover study

FAB RESEARCH COMMENT:

Findings from this new randomised controlled trial (RCT) are entirely consistent with those of the only previous such trial comparing the effects of a UPF vs a nutritionally matched whole or minimally processed diet on weight gain. See:

• Hall et al 2019 - Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake

That study involved healthy young adults living in the US - for whom the UPF vs non-UPF diet led them to consume an extra 500 calories/day, and gain almost a kilogram of weight in 2 weeks (as well as worsening various meaures of metabolic health)

This one involved overweight or obese adults in Japan - and found that their extra calorie intake on the UPF vs non-UPF diet was more than 800 calories/day, their weight gain was over 1 kg in just one week. 

Chewing of food per calorie was also significantly lower for the UPF than the 'real food' diet. This is consistent with the proposal that one reason why UPF promote overeating is the sheer speed with which they can be consumed - allowing less time for satiety signals from the gut to reach the brain. 

These very striking results are important - because a huge and ever-increasing body of research linking overeating and obesity to the consumption of UPF has to date been downplayed as 'insufficient to show causality" without additional evidence from human RCTs - not only by the food industry (who have a rather obvious vested interest) but by many academics, professionals and policymakers.  

Clinical and population studies consistently show that higher UPF intakes are firmly associated with

• obesity, Type 2 diabetes, cardiovascular disease and most other chronic health conditions
• eating disorders in which overeating is a key feature - such as bulimia and binge eating disorder, and
• 'food addiction' (still resisted as a concept by some, but well-recognised by the general public, and many health professionals) 

Similarly, there is now an abundance of supporting evidence from

• basic scientific studies identifying potential mechanisms by which features of UPF can affect appetite and metabolism in ways that promote overeating and obesity, and
• pre-clinical (animal) studies clealy showing that UPF lead to weight gain, obesity and related adverse outcomces for health and behaviour.

However, these many different kinds of converging evidence, all supporting the idea that high UPF consumption promotes overeating and obesity in humans (as well as higher rates of almost all forms of chronic disease, including mental health disorders), is dismissed by critics as 'inconclusive'.

The insistence that only RCTs can provide good evidence of cause and effect is easily refuted by the fact that no-one now disputes that smoking tobacco is a major cause of lung cancer - and yet this was never tested in human RCTs, for obvious ethical and practical reasons.

Similar considerations make RCTs of UPF diets in free-living participants exceedingly difficult to conduct. However, now that a second such trial has essentially replicated findings from the first, the case for delaying and/or denying the need for regulatory action to reduce UPF consumption in the interests of public health is weaker than ever.
 
See also:

• Obesity and Ultra-Processed Foods - News

• Obesity and Ultra-Processed Foods - Research

• Ultra-Processed Foods and addiction - News

• Ultra-Processed Foods and addiction - Research