On Monday my blog focused on the just one of the hazards associated with eating a high-carbohydrate diet, namely changes in markers of cardiovascular disease risk that would signal an increase in the likelihood of developing this condition. Other evidence exists which links diets of high glycaemic index (GI) and glycaemic load (GL) and an increased risk of cardiovascular disease (see here for more on this). Still other evidence links high GI and/or GL diets an in increased risk of conditions such as type 2 diabetes, gallbladder disease and breast cancer (more about this here).
While there is compelling evidence to incriminate blood sugar destabilising carbohydrates in chronic physical disease, less is known about the impact of such foodstuffs on brain function. In the longer term I suggest that lower-carb diets might be beneficial for reducing the risk of dementia. One reason for this is that high-carb diets are associated with an increased risk of insulin resistance/type 2 diabetes, which are risk factors of dementia. Also, high levels of insulin have been associated with an increased risk of dementia. You can read more about this here and here.
What about the shorter term, though? Could diets that are less likely to disrupt blood sugar and insulin levels be better for brain health day-to-day?
This month saw the publication of a study which assessed the effects dietary glycaemic load on mental function and mood . 42 individuals were randomised to eat either a low glycaemic load or high glycaemic load diet for a period of 6 months. The impact of these diets on ‘cognitive performance’ (brain functions such as vigilance, short-term memory and attention) as well as mood (as assessed by what is known as the Profile of Mood States (POMS) questionnaire).
The diets were not found to be different in terms of their effect of brain function. However, the high glycaemic load diet was associated with significantly worse outcome in terms of measures of depression. The authors of this study concluded that These findings suggest a negative effect of an HG [high glycaemic load] weight loss diet on sub-clinical depression.
One potential reason that high glycaemic load diet may be bad for mood relates to blood sugar imbalance. The brain, although it’s only about 2 per cent of the body weight, uses about a quarter of the sugar in the bloodstream. In other words, under normal circumstances, the brain is very sugar dependent. If it does not get that sugar in sufficient quantity, it can malfunction. This may manifest as mood issues including anxiety and/or depression. High glycaemic load diets are more likely to cause fluctuations in blood sugar, including sugar lows (hypoglycaemia), that in turn can trigger mood disturbance.
Because of this, it makes sense to avoid devoting too much of the diet to sugar-detabilising carbohydrates including those containing added sugar, as well as many forms of bread, potatoes, rice, pasta and breakfast cereals.
As far a mood maintenance goes, another approach that is worth bearing in mind is to ensure that the diet is relatively rich in protein. Amino acids (the building blocks of protein) provide the raw materials for crucial brain chemicals such as serotonin (mood enhancing, sleep promoting), catecholamines (which help with alertness, concentration and focus) and GABA (calming). In theory at least, a diet relatively rich in protein helps to fuel the brain with the very substances it requires to maintain optimal function.
1. Cheatham RA, et al. Long-term effects of provided low and high glycemic load low energy diets on mood and cognition. Physiol Behav. 2009 Jul 2. [Epub ahead of print]