Eating for the brain: do macronutrients matter?
Updated: May 23, 2021
What we eat affects our brains just as much as our bodies. Unfortunately, many people’s diets are not optimal, increasing the risk of getting unwell. Also, there is a strong link between physical diseases – such as diabetes – and mental health disorders. Alzheimer’s disease is now being dubbed Type 3 diabetes because there is a lot of overlap with the metabolic changes occurring in Types 1 and 2 diabetes.
As part of my PhD project I wanted to find out how macronutrients (carbohydrates, proteins and fats) affect short- and long-term brain function and which are the pathways by which macronutrients act on the brain.
Photo by Andrew Wong on Unsplash
Carbohydrates and fats – quality matters
Carbohydrates can be divided into simple and complex carbs. Simple carbs, or ‘sugars’, are linked to worse short-term and long-term outcomes for the brain. For example, each 60g of daily sugar intake (based on 12 months’ food intake) is estimated to age the adult brain as much as 10 years in terms of cognitive performance. Complex carbs (high in starch and fibre) may boost memory function because they slow the release of blood sugar, which helps determine how well our bodies and brains function.
Similar to carbohydrates, some fats (saturated fatty acids and trans fats) are linked to worse outcomes like poor memory function, while omega-3 is linked to better memory. The picture is less clear for fat types such as cholesterol.
The jury is still out on proteins
Whether a low or high protein diet is better for health remains a hotly debated topic in nutrition research. But protein intake becomes important when doing particularly difficult mental tasks, or if the environment places a lot of stress on a person. This is due to tyrosine, present in protein and responsible for making neurotransmitters (see below). In particular, old age makes us more vulnerable to environmental stressors and our bodies less resilient, making adequate nutrient intake even more important. Unfortunately, it has been shown that many elderly persons do not get enough protein from their diets.
How does food affect our brain?
Carbohydrate intake supplies glucose which is used by cells and the brain for energy. Glucose is the brain’s main fuel and its efficient use ensures optimal brain functioning. In contrast, impaired glucose and insulin metabolism is linked to processes like oxidative stress and inflammation which damages the brain. Over time this may lead to structural changes in the brain, such as decreased brain volume.
Macronutrient intake also affects the molecules from which neurotransmitters are made. These are chemical messengers present in the body and brain. In the brain, they affect things such as how we experience rewards, and thereby play a role in mood, decision-making and social behaviour for example. A single meal can affect social decision-making due to changes to the balance of neurotransmitters.
Food can also impact the composition and functions of the gut microbiome, which in turn has been shown to affect aspects of cognition and brain function (as discussed in other MindBodyMicrobiome blog posts).
Testing the link
My PhD will further explore how the macronutrients from our daily diet impact on metabolism and cognitive function. For example, do people eating a high protein diet have metabolic changes that changes cognitive function compared with someone who eats a low protein diet? To do that, I will observe people’s dietary habits and then invite them to the lab to look at their brain activity while engaging in a learning task and looking at their metabolic activity.
To sum it all up, macronutrient quality matters both in the short- and long-term. High sugar and saturated fat intake are linked to worse memory, while eating complex carbs and omega-3 is protective of brain function. For protein sufficient intake is important but there are still many unanswered questions. Macronutrients affect brain function mainly via glucose and insulin regulation, neurotransmitters and the gut microbiome.
This article was penned by Anne-Katrin Muth, a PhD candidate at Charité and the German Institute of Human Nutrition. We met during her trip to Melbourne in early 2020. Her recent publication on this topic is published in Clinical Nutrition.