Appliance of Science: Why is comfort food so... comforting?

Doughnuts, crisps, and ice cream may all be different in taste but they have one thing in common: These comfort foods contain just the right amounts of two key ingredients to give us that food high.

The most popular doughnut was the simple glazed doughnut, and it was found to have a sugar-to-fat ratio of 1:1.

What is your go-to comfort food? While the answers may vary, the content of fat and carbohydrates in our choices may be more similar than you’d expect.

Rewarding ratios

Studies have demonstrated that foods that contain both fat and carbohydrate (like sugar) are more rewarding, calorie for calorie, than foods that contain only fat or only carbohydrate. Not surprisingly, the foods that are constantly mentioned as comfort foods contain both fat and carbohydrate.

These foods create a response within the brain that lights up many areas associated with the reward system and the release of dopamine. Researchers suggest that we have separate systems in the brain to evaluate fat heavy or carbohydrate-heavy foods. When both systems are activated simultaneously the dopamine hit, and feeling of reward, appears to be larger than the sum of the responses individually.

Studies in rats have shown that they will regulate their calorie intake successfully when eating foods rich in carbohydrates or fats. However, this regulation process fails when presented with foods containing both carbohydrates and fats and the rats overeat.

Some studies have taken the investigation one step further; they found that not only do these reward-inducing foods contain both fat and carbohydrate, but they contain them in a very specific ratio… one part fat to two parts carbohydrate (1:2).

Food memory

Why is this ratio of fat to carbohydrate so important to us humans and where can we find it in naturally occurring foods? Foods like this do not usually occur in nature and tend to be created by human cooking and combining. There is one particular natural exception though than may fit the bill: Breast milk.

Human breast milk contains about 3%-4.5% fat and 6.5%-7.2% carbohydrate, pretty close to the 1:2 fat to carbohydrate ratio. Although the exact ratio will vary from mother to mother and even from feed to feed, it does suggest an optimal ratio for early human development. The reward system triggered while consuming this food in early life is likely preserved as an unconscious memory as we grow, and may be mimicked when we consume foods of a similar fat and carbohydrate ratio. These foods may bring comfort to people that were breastfed as they trigger the same comfort and reward responses as when they fed as infants.

The doughnut ratio

Personally, I am not a big fan of doughnuts, but judging by the number of new shops selling nothing but these culinary confections, I am in the minority. Not surprisingly, doughnuts contain both fats and carbohydrates, so they are already likely candidates to trigger our reward system. But with such a variety of different doughnuts to choose from (there are probably more than 100 different types) is there one that is considered more rewarding than others? A simple study was carried out during the filming of a 2014 series investigating fats versus sugars in our diet. Members of the public were offered free doughnuts and the fat-to-sugar content of each type was measured. The most popular doughnut was the simple glazed doughnut, and it was found to have a sugar-to-fat ratio of 1:1, a sweet spot for doughnuts it seems.

I may not like doughnuts but I am very partial to ice cream. I haven’t yet found a study reporting which type or brand of ice cream has the perfect reward-inducing ratio, so I may just have to conduct a study of my own, in the interest of science, of course.