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]
Another excellent blog, John, and my two-penneth is to offer strong agreement in that the link between food and mood is, or has the potential to be, a strong one; it is one I have experienced first hand and I think it manifests itself at two levels. Amongst the wider population and many medical practitioners the link is often and sadly disregarded.
As you say, unstable blood sugar and dips in blood sugar can cause mood swings; as a parent I have seen this in a child. However, my first person experience is of a type 2 diabetic not prescribed medication. Here my experience points the finger at consistently raised BG. If I don’t give my condition the attention it deserves and persist in a diet of high GL I have on more than one occasion experience something I call a diabetic depression.The symptoms are physical lethargy and mental dullness. The mental aspect can be really debilitating; poor concentration, negative outlook, lack of engagement, inability to plan, etc. The condition creeps up slowly and is not recognised until function is considerably impaired, least not by me, yet once recognised some exercise and dietary care can transform my outlook in a matter of a few days. The last experience lasted 2-3 months and really brought it home. I hope not to be fooled nor be so foolish again. What charachterises these periods is a high BG reading on the meter. (I ought to habitually test- but I don’t) That’s an explanation of one level.
Diabetes is acknowledged as a chronic illness, one that is a long time in the making. Now with hindsight, I sometimes wonder if the factor(s) that contributed to the development of the condition while not recognised were significant in shaping my personality or limiting my acheivements. It is impossible to be anything other than subjective over this but I lean towards thinking they were. So that is my offering as an explanation for a second manifestation.This gives me concern for todays’ emerging generations.
My diabetics perspective would be to contribute that high BG has a bearing though there is still much to wonder about the disruptive process, the inflammatory role of insulin, and chain reactions. GL appears a powerful tool to help us regulate and stabilise BG and maintain it a sustainable and healthy levels.
Octane powers my car but it is not set to run on high octane fuel – just the regular unleaded.
Given the scrutiny they deserve the highest GL foods, the ones humankind regards as calorific staples such as refined cereals, rice and potatoes, do resemble high octane fuel that ought to be accorded greater respect. Like my car, I am not sure my body is set to run on them with a high dependency or for a protracted period of time. Evolution has not prepared me.
Excellent information — thank you. This is a new angle to me. I’m especially interested in the link of insulin resistance to dementia, and by implication to brain function. That makes sense of what is seen anecdotally among people with high insulin resistance. There is often an emotional as well as physical implication.
Excellent stuff! And my experience parallels that of Chris. I have diagnosed (Atypical) depression, with a side order of Seasonal Affective Disorder and a free sample of ADD (without hyperactivity). All these symptoms have reduced remarkably with carb restriction and I am convinced the reactive hypoglycemia I used to get was the cause.
In a way it makes evolutionary sense, I am designed to hyperfocus while collecting nuts and fruits in autumn, stuff my face, then go torpid until spring. This does not fit well with modern civilisation.
Keeping the BG level by avoiding carbs and eating more fat and protein seems to switch off the genes.