Hedonic hunger: What does the science say?

Ultra-processed foods

What is ultra-processed food? The answer can vary, depending upon the source you read.

The NOVA classification, originally developed in Brazil, is the most commonly used system to define the degree of food processing. This classification states that ultra-processed foods are mainly “ready-to-eat industrially formulated products that are made mostly or entirely from substances derived from foods and additives, with little if any intact group 1 (unprocessed or minimally processed) food.”

Examples include “sugar-sweetened beverages, sweet and savory packaged snacks, reconstituted meat products, pre-prepared frozen dishes, canned/instant soups, chicken nuggets, ice cream,” and others.

Regardless of the exact definition, ultra-processed foods have become a large source of calories for most Americans. Observational studies consistently report an association between higher consumption of ultra-processed foods and increased risk of chronic health conditions. And other studies suggest ultra-processed foods have the most addictive-like properties.

One of the best and most tightly controlled studies to investigate how ultra-processed food affects caloric consumption was conducted by Dr. Kevin Hall and colleagues. and published in Cell Metabolism in 2019. The study reports intake increased by more than 500 calories each day for those eating as much as they wanted from meals composed of ultra-processed foods when compared to another group eating as much as they wanted of meals made from whole foods. Importantly, the meals were designed to be matched for presented calories, energy density, macronutrients, sugar, sodium, and fiber; only the degree of processing was varied. 

This randomized controlled trial is novel in suggesting a causal relationship between ultra-processing of food and increased calorie consumption. What the study design did not address is the question of why consuming ultra-processed food would lead to consuming more calories.

Many other studies suggest overeating is caused by certain combinations of fat, salt, and sugar, and the hyper-palatable nature of these food products. But the study by Hall suggested this may not be the case and instead it is more about the level of processing itself. For instance, does a baked potato with cheese, bacon, and sour cream create the same desire to overeat as an ultra-processed bacon and cheese-flavored potato chip?

Controversy still exists about the precise underlying mechanism that stimulates overconsumption when diets are high in ultra-processed food. But it seems clear that more processing alone triggers more consumption, even if it isn’t the only reason.

---

Carbs and sugar

Many studies suggest that carbohydrates, and especially sugar, stimulate brain reward centers — triggering us to eat more of the food product. Animal studies suggest this stimulation can be similar to the stimulation delivered by addictive drugs.

Human studies demonstrate higher glycemic index and higher carbohydrate foods stimulate brain reward centers more than lower glycemic index or lower carb foods.

However, many questions remain unresolved, and the concept of sugar and carbohydrate addiction is controversial among scientists and policymakers. For instance, clinical experience suggests it is unlikely that high carb diets based on whole, low glycemic index foods are as stimulating or addictive as processed, high sugar foods. 

Clinical experience also suggests that not everyone has the same tendency to be triggered to overeat by refined high glycemic carbs or sugar. Just like some people can have one beer and then stop, some people can have one french fry or one bite of a cookie and stop. Others find stopping much more difficult.   

Knowing how likely it is that sugar and carbs will trigger you to eat more is a good place to start. If you find yourself strongly triggered, it’s best to avoid those foods.

---

Carbs and fat together

It’s common to find naturally occurring foods that contain protein and fat, such as steak, eggs, and salmon. It’s also common to find carbs alone in nature — think of fruit and potatoes. But, aside from nuts and the milk that mammals make (including breast milk) for nourishing offspring, it is rare to find unprocessed foods that combine carbs and fat.

That’s important, as it points out the evolution-diet mismatch that exists for foods combining fat and carbs. This suggests that adult humans did not evolve eating these foods. Yet tasty, calorie-laden combinations are plentiful in our modern food supply. 

Furthermore, combining carbs and fat together triggers greater cravings than either macronutrient alone.

What remains unclear (at least in human studies) is whether combining natural fats and carbs, such as a rib-eye steak and sweet potato, has the same stimulating effect. Again, it may come back to the level of processing that combines carbs and fats in a single ultra-processed product.

---

Salt

Salt is another ingredient that contributes to increased palatability and calorie overconsumption.

One randomized trial found that adding salt to either high fat or low fat meals increased calorie intake by 11%. The authors hypothesized that salt may “override fat-mediated satiation.”

And, as we discussed in our podcast with author Michael Moss, processed food companies purposefully add salt to their products to increase the “addictive potential.” 

Again, controversy exists regarding the question of whether salting your vegetables or your steak also contribute to overeating. It may, or it could be that salt’s strongest hedonic effects are on energy-dense and ultra-processed foods.

Making sense of it all

It’s clear that there is conflicting information about exactly what drives overeating. Hedonic factors are a piece of the puzzle.

Ultra-processed food seems to have the strongest evidence, regardless of the macronutrient (or micronutrient) makeup. But salt, sugar, high-glycemic carbs, and fat — especially in combination — also appear to stimulate overeating.   

Of course, there is a great deal of crossover, as most ultra-processed food products are a mixture of salt, sugar, high-glycemic-index carbs, and fat.

But the confounding factors don’t stop there. Ultra-processed foods are usually inexpensive, widely available, and heavily marketed. They’re also engineered to taste just right. That makes it difficult to separate the “real world” effect of product development, marketing, convenience, and affordability from the level of processing and nutrient composition. 

Yet the conclusion seems clear: It is best to avoid ultra-processed food products and foods that combine sugar, fat, and salt, focusing instead on whole foods.

---