Why combining fat and carbohydrate is a recipe for overeating

Have you ever wondered why hot toast with lashings of butter is so comforting? Or why you crave chocolate? Or why it’s almost impossible to stop eating Pringles until you’ve demolished the whole tube? There’s a lot going on here, but one factor is the high levels of both fat and carbohydrate in these foods. Our brains find this combination extremely pleasurable, and practically irresistible.

The more rewarding a food is, the more we crave it, the more we seek it out, and the more we eat of it when we find it. The reward value of food, therefore, is an important driver of appetite regulation and calorie intake.

When we eat food containing fat or carbohydrate, these macronutrients are ‘sensed’ in the small intestine, a message is sent to the brain, and dopamine is released. This makes us feel good. It’s a clever mechanism to make us repeat the eating behaviour that brought these calories into the body. This was crucial to survival in a world of barely enough calories. A world of unprocessed food. A world where foods high in fat and carbohydrate were very rare (in fact, I can’t think of any).

Today, we have many foods with high proportions of fat and carbohydrate. Eating these foods seems to trick the brain into overestimating the calorie content, inducing an outsized dopamine response. A overgenerous reward.

In a 2018 study, researchers from Europe and North America investigated the reward value of a range of foods using a money-based bidding exercise and brain scans. They tested high-fat foods, high-carbohydrate foods, and high-fat/high-carbohydrate combination foods. The results showed that the human brain values high-fat/high-carbohydrate combination foods more than either high-fat or high-carbohydrate foods. In fact, the effect was supra-additive (in other words, it was greater than the sum of its parts), and it was independent of other factors that influence reward value.

This empirical evidence supports what all know intuitively. A piece of dry toast is not particularly pleasurable to eat. Nor is a tablespoon of butter. But put them together, and you have something altogether different. Something delicious. Something properly rewarding. There are other factors involved in this reward equation, but the high-fat/high-carbohydrate combination is one of the most important.

Why does this matter? Because eating highly rewarding foods drives nonconscious overeating. And overeating is the primary driver of weight gain and associated health problems such as diabetes.

Of course, ultra-processed junk foods (as always) are the worst culprits here. Pizza, ice cream, chocolate, French fries, crisps, biscuits, cakes, pastries, etc. They can be occasional treats, but shouldn’t be staples.

It’s also easy to create rewarding high-fat/high-carbohydrate foods at home. Toast with butter, roast potatoes, pasta or rice with a rich and fatty sauce, dates with peanut butter (a favourite in our household), desserts and puddings. How much of these foods should you eat? That depends on a whole host of factors, including your level of physical activity, your body composition goals, and your metabolic health status.

If you want to reduce calorie intake, to lose or maintain weight, you should consider reducing your intake of high-fat/high-carbohydrate combination foods. This is probably one mechanism by which low-fat diets and low-carbohydrate diets exert their weight loss effects. If you want to increase calorie intake to fuel large amounts of physical activity, for example, try introducing more of these foods (primarily the fresh, homemade, nutrient-dense variety, of course).

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