In medical training, we were taught that weight control was as simple as grade school math: calories in < calories out = weight loss. Eat less, move more, problem solved.
So, why then have obesity rates continued to rise, measuring in at 40 percent of Americans in 2021-2023? It’s because our brains evolved during times of caloric scarcity to resist weight loss and prefer high-calorie-density food. This makes today’s food environments, where highly rewarding food fills the shelves, highly problematic. The more we reduce our calorie intake, the more loudly our brains urge us to consume more, and we’ve all got a ready supply.
Recent study
Does that mean we’re all doomed? A recently published study in Nature Medicine indicates we are not. Its findings add to the growing pile of evidence that changing what we eat, rather than focusing so much on how much we eat, is the overlooked key to the puzzle.
Dr. Dicken and his group reported on the results of a randomized clinical crossover trial in 55 overweight individuals who habitually ate more than 50 percent of their calories as ultra-processed food (UPF). Participants were randomized to either an ad libitum UPF diet or a minimally processed food (MPF) diet; after eight weeks, participants were switched to the other diet. Participants were given all meals, snacks, and drinks for both diets—each of which followed U.K. nutritional guidelines.
While both diets were matched in nutrient levels and maximum energy intake (4,000 kcal/day, though participants could eat less), the MPF diet was associated with significantly more body weight loss (2 percent) than the UPF diet (effect size of 0.5), in addition to more fat mass loss and reduced triglyceride levels.
Similar separations between MPF and UPF diets on body weight have been documented in other randomized trials where calorie consumption was not controlled.
By what mechanism did the MPF diet promote weight loss in this study? Primarily, it made people eat less. On average, the MPF diet reduced participant calorie intake by 170 more kcal per day than the UPF diet did.
Why do diets rich in whole foods cause people to eat less?
For one, whole foods are less energy-dense than UPFs. Food consumption stretches receptors in the stomach, which promotes satiety via vagus nerve activation, which feeds back to the brain to integrate with signals from neurohormones like leptin to influence eating behavior. Highly rewarding foods with lots of fat and sugar inhibit vagus nerve activation and reduce the desired inhibitory effects of eating.
Second, as reported in the aformentioned study, participants on the MPF reported reductions in “hedonic appetite” (meaning an appetite motivated primarily by pleasure seeking) and greater reductions in cravings despite greater weight loss. UPFs are engineered by the food industry to be more rewarding, and often contain high levels of sugar, which can fuel hedonic eating.
Hedonic eating is controlled by the same brain circuitry that drives the use of nicotine, alcohol, and other drugs of abuse. Over time, just like with other addictive substances, overuse of high-sugar processed foods leads to long-term changes in emotional, cognitive control, reward, and motivational circuits, which makes it increasingly difficult for people to control their use of these especially rewarding foods.
Does quality win over quantity when it comes to weight loss?
Although there’s much to be learned about how to best address obesity and addictive eating, one thing is becoming increasingly clear: Food quality matters because it changes our brain. The better we eat, the more likely we are to make better choices.
The original version of this post also appears on the Psychiatric News Blog.