Pizza, desserts, fast food, and soda are all foods that bring us comfort. We are so inclined to eat them that a diet high in fat, sugar, and processed foods has become known as a Western diet. We continue to binge on these foods despite the known links to obesity and other serious health risks, like diabetes. But did you know that this diet is also linked to cognitive impairment? A recently published paper reviewed the research on mouse models that link the Western diet to anxiety and learning/memory difficulties.
The effect of a Western diet produced a chicken and the eggs problem.
Research has found that children in the U.S. are fed far more unhealthy foods than is healthy. Children have diets that are high in saturated fats and sugars. There has also been a shift towards eating more. The combination of poor eating and larger portions has led to an obesity issue. In the U.S., 18% of children are obese, the majority of which will remain obese.
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Emerging evidence has also linked childhood obesity to lower performance on cognitive tasks. So, this poses the question, is obesity causing lower cognitive function, or is the diet?
Mouse models are needed to study this issue.
It is not ethical to purposely raise a child on a poor diet to monitor the negative effects. So, researchers use mice. Mouse models allow researchers to rigorously control all aspects of the experiment to understand what factors impact development in mice.
Researchers can simulate a Western diet in a couple of ways. They can give mice food that is high in fat and simple sugars, or they could simulate the choices we make. This is called a cafeteria diet. The mice are allowed to chose what they wish to eat and are given a selection of healthy and unhealthy (but tasty) options.
Sugar and fat are linked to anxiety.
In humans, there has been a link between eating high amounts of sugar and fat with higher levels of anxiety. This observation has been confirmed in mouse models. When mice are fed a high-sugar diet they become more anxious.
Obviously, it is hard to tell the mental state of a mouse. So, researchers look for behavioral changes. Anxious mice are less likely to explore new environments, try new foods, or socialize with other mice. Researchers can also monitor the blood levels of mice because anxious mice have higher levels of stress hormones.
Not all diet-induced behavior change is long-lasting. Diets fed to adolescent mice had life-long consequences, but diet changes in adults only created temporary behavioral changes. The sex of the mouse mattered too. Adult males fed chocolate chip cookies became more anxious for a while, but the females did not. So, if you give a mouse a cookie, make sure it is female.
It can be difficult to test a mouse’s memory or learning.
There are several tests researchers use to assess a mouse’s memory and learning. The classic mouse in a maze experiment tests their spatial memory, but researchers can also test object recognition. They do this by giving a mouse an object that gives them a shock. Later, when the mouse sees the object again, the researchers expect that the mouse will avoid it. A more pleasant memory test could include learning a series of tasks to get a treat.
Once a mouse is fed or raised on a Western diet, they perform significantly worse on all of these behaviors.
Mice are not people, but we can learn from them.
It is difficult to make the leap from mouse models to human behavior. However, this study points out that we are already seeing similar patterns in human populations. This study was not trying to determine IF there is a trend; it wants to know the cause of the trend. Obesity is a growing concern. But, if it is the diet that is harmful, not obesity, it means that even those that do not show outward effects of poor diet may still be suffering the important cognitive consequences. This can have important medical and lifestyle implications.
