Saturated Fat, Sugar and Your Brain
Worldwide obesity has more than doubled since 1980 with more than 1.9 billion people now being classified as overweight or obese. According to the World Health Organisation (WHO), the fundamental cause of obesity is an energy imbalance, that is, more calories being consumed than calories being expended. The most likely causes of this imbalance are (a) an increased intake of energy-dense, high-fat foods; (b) a lack of sufficient physical activity. Either or both of these things can lead to an increase in body fat and/or in BMI which in turn increase the risk of heart disease, stroke, diabetes and cancer. Interestingly, it is possible that the consumption of sugar-rich and high-fat foods may also cause changes in our brains.
A scientific paper published in 2011 reviewed evidence that the so-called ‘Western’ diet (high levels of saturated fats and simple sugars such as glucose and sucrose) might interfere with the function of a deep-brain structure called the hippocampus. The hippocampus is responsible for many aspects of learning and memory and damage to it can lead to significant difficulties learning new tasks and recalling memories. Indeed, people who suffer from Alzheimer’s disease often have significant damage to their hippocampi which accounts for the memory loss and other behaviour changes they experience.
Saturated fats are found in many foods, the majority of which come from animal sources. Beef, lamb, dairy products, fried foods and palm oil are all high in saturated fat and the consumption of large amounts of these types of foods has been linked to hippocampal dysfunction and increased incidence of Alzheimer’s disease. Indeed, rats fed a diet high in saturated fatty acids and sucrose perform worse on tasks designed to test the function of their hippocampi; they show a lack of ability to navigate through a simple maze and find it harder to remember how to solve the same maze when trying to navigate it again. What is especially interesting is that these effects can be seen before the rats show significant weight gain. This means that the effect of saturated fat and sugar on the brain may not be related to body fat or BMI.
But how could eating sugary or fatty foods affect how the brain works? It might be that eating foods that are high in simple sugar causes the body to produce a large amount of insulin to try to bring sugar levels in the blood back to normal; this spike in insulin may interrupt brain signals to and from the hippocampus meaning that memory and learning ability is reduced. Indeed, eating a meal which is high in sugar can impair memory function 1-2 hours later.
Another way a diet high in saturated fats and simple sugars might impair memory and learning is by reducing the production of a brain protein called BDNF. BDNF is important in making new connections in the brain in response to learning new tasks and also helps in the production of new cells which allow the brain to function efficiently. Diets high in saturated fat and simple sugars may reduce the amount of BDNF produced in the hippocampus meaning that new memories are harder to make.
‘Western’ diets may also cause damage to the protective layer around the brain which stops toxins getting in and causing damage. Once toxins get into the brain they can destroy healthy cells and/or cause the brain to stop making new cells in order to fight the damaging ones off. One study found that body fat in women was significantly related to how strong the protective layer around their brains were. A weaker protective barrier is related to poorer performance on memory and learning tasks and to the presence of Alzheimer’s disease.
What the research shows is that it may not just be the body that is affected by a diet high in saturated fat and simple sugars; there might be an effect on the brain too. Although it is not known how that effect might take place, early research has shown that learning and memory might be particularly affected.
 Kanoski, S. E. & Davidson, T. L. (2011) Western diet consumption and cognitive impairment: Links to hippocampal dysfunction and obesity. Physiology & Behaviour, 103 (1), pp 59 -68