Diet and dementia: what the research tells us
Dying and dementia are the two things people in their middle years tend to say they are most apprehensive about. The former is inevitable, but can the latter be avoided? A number of studies have shown an association between exercise, in particular resistance or muscle-building exercise, and a decreased risk of Alzheimer’s disease and other forms of dementia. The jury appears to be still out on the possible protective effects of brain training. But what about the food we eat?
Diet and dementia has been an intensive area of research, and the best way to learn anything from the myriad studies carried out with varying methods, objects and endpoints is to look at the meta-analyses and systematic reviews. The most recent review, published late last year, looked at all observational studies published between 2014 and 2016 on the relationship between diet and late-life cognitive disorders. This found evidence that combinations of foods and nutrients can act synergistically to provide stronger effects than found with any one particular ingredient. In particular, adherence to a Mediterranean-type diet – with its emphasis on plant-based foods, fish, poultry and olive oil – was associated with decreased rates of cognitive decline.
The review also finds another diet associated with a reduction or delay of Alzheimer’s disease: the emerging DASH – or Dietary Approach to Stop Hypertension – diet, which emphasises fruit, vegetables, whole grains and low-fat dairy foods. It includes meat, fish, poultry, nuts, and beans, but limits sugar-sweetened foods and beverages, red meat, and added fats. As its name suggests, it was originally designed to help in hypertension, which has in itself been linked to higher rates of dementia.
Combining the Mediterranean and DASH diets produces the MIND diet, or the Mediterranean-Dash diet Intervention for Neurodegenerative Delay, which has also been associated with lower rates of dementia in several studies. Put together by a team from the Rush University Medical Center in the US, the MIND diet, like the other two diets, emphasizes the importance of fresh fruit, vegetables, and legumes. But it also includes recommendations for specific foods, such as leafy greens and berries, which have been shown in studies to slow cognitive decline.
The MIND diet appears to be more effective at reducing cognitive decline than either the Mediterranean or DASH diets on their own. One prospective study of over 900 middle-aged and older people, followed for an average of nearly five years, found those with either moderate or high compliance to the MIND diet had significantly lower rates of Alzheimer’s disease diagnoses, with a reduction in risk of a third and a half, respectively, compared with the lowest levels of compliance. But for the DASH and Mediterranean diets, only study participants with high adherence saw an effect.
Another study of around 1000 people found that adherence to the MIND diet significantly slowed cognitive decline, and that those with the highest compliance managed to delay decline by an average of 7.5 years.
Systematic reviews of these dietary interventions do caution that it is very difficult to tease out possible confounders; that more long-term results are needed; and that observational studies can never show causality, only association. Of course, it’s notoriously difficult, and indeed probably impossible, to run a randomised trial of a dietary intervention over many years. That’s not to say we will never get evidence that most in the medical community consider definitive. After all, no randomised trials were ever carried out to prove the link between tobacco use and lung cancer, and yet today there is no doubt at all about the causality.
In the meantime, here are the fundamentals of the MIND diet:
What to eat:
- Green leafy vegetables – kale, spinach, broccoli, collards and other greens, at least two servings a week;.
- Other vegetables – a salad and at least one other vegetable every day;
- Nuts – at least five times a week;
- Berries – such as blueberries or strawberries, at least twice a week;
- Beans – three times a week;
- Whole grains – at least three servings a day;
- Fish – at least once a week;
- Poultry – two or more servings a week;
- Olive oil.
What to avoid:
- Butter and margarine – not more than one tablespoon daily;
- Cheese – less than once per week;
- Red meat – no more than three servings each week;
- Fried food – less than once per week;
- Pastries and sweets – no more than four times a week.