The effects of a cafeteria diet

A new study published in Physiology & Behavior shows that rats gain weight when they eat foods such as chips, cakes and candy typically sold in a cafeteria – but this surprisingly does not affect their behaviour.

The researchers involved in the study had expected that what many researchers call a cafeteria diet would lead to more of the anxiety- and stress-like symptoms observed among both animals and people, with obesity often linked to mental disorders, but this was not the case.

The results made the researchers more aware of the possible physiological differences between people and animals, when animal experiments can be a model for what happens to people who eat an unhealthy diet and when animal experiments are not relevant.

“The study is part of a larger research project that aims to determine what happens in the brain when people eat too much and have an unhealthy diet. Our experiments in animals enhance our knowledge about the changes in humans we should look for in our future studies,” explains a researcher behind the study, Christakis Kagios, a PhD Fellow from the Department of Medical Science, Uppsala University, Sweden.

Investigating a more realistic diet

In recent years, intensive research has sought to understand how different types of diet affect both physical and mental health.

For example, many studies have been carried out on how a typical Western diet with a high fat and sugar content affects obesity and the risk of developing cardiovascular disease, diabetes and mental disorders.

Much research has also been performed on whether the “Mediterranean diet” or a vegetarian diet can promote health. In the new study, researchers aimed to determine how a cafeteria diet affects health.

“Studies on the effects of a cafeteria diet are becoming more common since it more closely reflects what many people eat. Other animal studies have examined the effect of eating a fat- and sugar-rich Western diet, but these studies often use a diet with a fat content exceeding 50%, which is not very relevant for humans. In contrast, the cafeteria diet is closer to what many people eat on a daily basis,” says Christakis Kagios.

Experiments on male Wistar rats

The researchers investigated what happened to rats’ weight and behaviour when fed a cafeteria diet for 12 weeks.

The rats were divided into three groups, with the control group fed normal rat chow, the second group fed a cafeteria diet, and the third group fed rat chow but kept in a caloric deficit to achieve 85% of the weight of the control group.

The rats were measured and weighed twice a week during the experiment, and the researchers examined their behaviour with a test that assesses a broader behavioural repertoire to identify how risk-averse they are, how curious they are, how much time they spend in open areas and how much time they spend in hiding.

Cafeteria diet resulted in considerable overweight

The research showed that the cafeteria diet strongly affected the rats’ body composition. Compared with the rats fed rat chow, rats on the cafeteria diet gained more weight and ended up having about 20% more body weight and substantially more body fat.

Blood tests also revealed that the rats underwent considerable metabolic changes of the type that can lead to developing many metabolic disorders, which was not surprising since people react similarly.

However, the cafeteria diet did not affect the rats’ behaviour, which was unexpected.

“This was surprising because we know that obesity among people is associated with mental disorders such as anxiety and stress. This made us think about what the causal link might be. Does an unhealthy diet cause anxiety and stress, or do people who have stress and anxiety eat a more unhealthy diet?” asks Christakis Kagios.

Aimed to determine what happens in the brain

According to Christakis Kagios, the study contributes to research on how an unhealthy diet affects health.

Using a rat model of how a cafeteria diet influences the development of obesity and changes in behaviour gets closer to showing how this might affect people.

However, Christakis Kagios emphasises that the study also shows that the effects on animals of eating a cafeteria diet cannot fully be transferred to people.

He explains that the next step in the research will be to investigate what exactly happens in the brain of animals: for example, by examining how eating a cafeteria diet changes the levels of hormones and neurotransmitters – to better understand what might happen to people.

“We also need to improve our understanding of which components of a cafeteria diet are important for the effects we observe. Evidence indicates that some combinations of food items affect stress, and other combinations do not. This needs to be studied in more detail,” explains Christakis Kagios.

Examined people with type 2 diabetes

Professor Jan Eriksson, who led the project and is from the same department as Christakis Kagios, says that the research is an early part of a major research programme in which the researchers will investigate how high calorie intake and overweight among people affect the development of type 2 diabetes and how the brain is involved.

The rat studies help to guide the researchers in determining which areas in the brain could be relevant when examining changes connected with the development of overweight and obesity.

The researchers are currently conducting a major study, also guided by studies of rats, examining changes in how the brain regulates hormones and blood glucose and the behavioural implications for people with type 2 diabetes.

“There is complex interaction between food intake and the brain, but this is not well researched. For example, in some experiments people are instructed to eat extra food, and the same mental disorders are not observed among these people as among people who have obesity that develops outside a research setting. We aim to understand why having overweight for many people is associated with an increased risk of developing mental disorders but not for others – and how diet affects this,” concludes Jan Eriksson.