Ultraprocessed foods make you overeat – even when you don’t want to – and cause weight gain

If you’ve been reading my articles for a while, you’ll have gathered by now that I’m a total nerd when it comes to nutrition research. I’m one of those strange people who get very excited by an elegant study design that takes an intelligent approach to an important research question and yields insights that are not just interesting, but immediately applicable in my practice.

And that makes Kevin Hall one of my favourite researchers to fan-girl over, because when it comes to brilliantly-conceived and meticulously-executed research that addresses answers key questions about nutrition, he knows how to deliver the goods.

Hall’s background is in physics rather than nutrition science, which not only equips him to develop some pretty mind-bending mathematical equations relating to human metabolism; it also gifts him with the objectivity to wade into some of the thorniest debates in the world of human nutrition without having ‘a horse in the race’.

Hall is a dietary agnostic, unattached to any dietary philosophy including low-carb, Paleo, plant-based and low-fat. He’s just a very curious guy, who knows how to design studies that satisfy his curiosity to discern dietary truth from fiction.

Previously, in 2015, Hall and his research team showed that reducing dietary fat resulted in greater loss of body fat than reducing carbohydrate intake.

Then in 2016, he tackled the primary argument used by advocates of ketogenic diet protocols – that ‘a calorie is not a calorie’ and that slashing carbohydrate intake and replacing it with fat ramps up metabolic rate, allowing people to lose weight without restricting energy intake.

In fact, using state of the art tools to measure body composition and metabolic rate, Hall demonstrated that fat loss slowed down on a ketogenic diet and fat-free mass (comprised of internal organs, muscles, bones and water) declined. The much-vaunted boost in metabolic rate was barely detectable.

His latest study, published in July 2019, is the first randomised controlled trial designed to assess the impact of ultraprocessed foods on ad libitum energy intake – that is, how many calories people will consume when given free rein – and on a slew of biomarkers.

Ultraprocessed foods, as I’ve discussed previously in my article Food to die for, is defined as “formulations mostly of cheap industrial sources of dietary energy and nutrients plus additives, using a series of processes”.

These ‘edible food-like substances’, as food writer Michael Pollan has dubbed them, are high in energy, salt, sugar and fat, and engineered to be irresistible (as I discussed in my previous article Why are salt, sugar and fat so addictive?

Stripped of the fibre that forces us to chew, their texture and mouthfeel facilitate overeating. Their energy density provides a supernormal stimulus to reward centres in our brain, causing addiction-like behaviour. They may even disrupt the gut-brain signalling that alerts us when we’ve had enough to eat.

But while there is plenty of circumstantial evidence linking the global pandemic of obesity and type 2 diabetes with the exponential growth of the industrialised food system and its relentless colonisation of every inhabited continent on earth, objective proof was lacking:

“No causal relationship between ultra-processed food consumption and human obesity has yet been established. In fact, there has never been a randomized controlled trial demonstrating any beneficial effects of reducing ultra-processed foods or deleterious effects of increasing ultra-processed foods in the diet.”

So Hall and his coworkers went in search of the smoking gun, designing a study in which 20 young adults – 10 males and 10 females – volunteered to stay in a metabolic ward for 4 weeks, eating either an ultraprocessed or unprocessed diet for 2 weeks, and then switching over to the opposite diet.

What did they find? The article’s title kind of gives it away: Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake.

The genius of the study design is that all meals were matched for energy (calories/kilojoules), energy density, macronutrients, sugar, sodium and fibre, neatly handling each of the characteristics of ultraprocessed foods that are believed to trigger overeating.

Here are some of the meals that participants were served during the study; first the ultraprocessed menu:

… and then the unprocessed menu:

Naturally, the sources of each of those nutrients varied dramatically: 54% of the total sugar in the ultraprocessed meals was derived from added sugar while only 1% of the total sugar in the unprocessed meals was added. Fibre intake during the ultraprocessed diet phase could only be matched by adding a soluble fibre supplement to beverages and yoghurt served with the meals.

Saturated fat comprised 34% of total fat intake during the ultraprocessed diet phase compared to 19% during the unprocessed phase, and the ratio of oega-6 to omega-3 fatty acids was 11:1 versus 5.1 respectively. ultraprocessed

The energy and macronutrient content of each meal and snack was precisely calculated using dietetic software. Participants were given 3 meals per day as well as snacks, and instructed to consume as much or as little as desired; leftovers were weighed in order to accurately measure each participant’s energy intake.

On average, participants consumed an extra 508 calories per day during the 2-week ultraprocessed diet phase than they did during the unprocessed food phase, eating an additional 280 calories from carbohydrate and 230 from fat. They gained an average of 900 g (including 400 g of extra body fat) while eating ultraprocessed foods, and lost 900 g (300 g of it from body fat) while eating unprocessed foods.

Insulin secretion and blood glucose level were increased during the ultraprocessed diet phase, indicating a decline in insulin sensitivity.

On the other hand, the appetite-suppressing hormone PYY increased, and the appetite-stimulating hormone ghrelin decreased, on the unprocessed diet.

Total cholesterol, high sensitivity C-reactive protein (a marker of inflammation), fasting glucose and insulin levels also dropped on the unprocessed diet.

Interestingly, participants rated meals from each phase roughly equally as pleasant and familiar, indicating that they weren’t eating less of the unprocessed meals because they found them unappealing.

However, measurements of their meal eating rate revealed that they ate the ultraprocessed meals much faster. Rapid eating is known to delay ‘satiety signalling’, the process by which stretch receptors and nutrient sensors in the gut alert the brain that sufficient food has been consumed.

If you’ve made it this far, I’m guessing you’re a big ol’ nutrition nerd like me, so let’s take a moment together to really savour what a fine example of research this study is, and how mind-bending are its ramifications.

OK, that was fun.

Final thoughts: The fact that meals were matched for energy, macronutrient and fibre content, but participants still ate 500 calories more per day of the ultraprocessed foods, sends a stark message: the ‘diet foods’ industry has nothing to offer us when it comes to weight loss success.

There is no known way to engineer an ultraprocessed food that can make it a match for simple, unprocessed foods such as fruits, vegetables, whole grains and legumes, when it comes to satisfying our appetites and allowing us to eat as much as we desire, and still lose weight… or maintain a healthy weight.

Mother Nature had the answer, all along.

Struggling to lose weight? Confused by all the ‘noise’ from competing dietary camps about the best way to lose weight and keep it off? Apply for a Roadmap to Optimal Health Consultation today, and let’s clear the confusion and get you on the right track to success.