The DASH Diet may help prevent Alzheimer’s

Another popular diet that’s shown promising results in reducing the risk of developing Alzheimer’s disease (AD) and other age-related dementias is the DASH diet.  DASH stands for “Dietary Approaches to Stop Hypertension.”  The diet was created by doctors 25 years ago to help treat or prevent high blood pressure.  While the DASH diet does a great job of lowering blood pressure, several studies have found that it is also good for the brain.  Older adults with high blood pressure have a much greater risk for cognitive decline, AD, and vascular dementia.  In fact, high blood pressure affects more than half of all adults ages 60 years or older (Smith et al., 2010).

The DASH diet was designed to lower sodium intake.  The average American’s diet contains some 3,400 mg of sodium a day.  There are two versions of the DASH diet.  The original diet allows up to 2,300 mg of sodium a day.  A revised diet reduces sodium for people with hypertension to only 1,500 mg a day (Heller, 2016).  Both DASH diets emphasize eating vegetables, fruits, and low-fat dairy.  DASH dieters can eat moderate amounts of whole grains, fish, poultry, and nuts.  Lean red meat, sweets, and fats are allowed, but only in small amounts.

To assess the cognitive benefits of the DASH diet Smith et al. (2010), recruited 124 participants with elevated blood pressure who were sedentary and had body mass indexes between 25 and 44.  Participants were randomly assigned to three groups for the four-month study; a DASH diet but no exercise group, a DASH diet plus exercise group, and a control group that didn’t exercise or follow the DASH diet.

The DASH diet only group were shown how to modify their diet but received no exercise encouragement or instructions.  The DASH diet plus exercise group was given the same dietary advice but also attended three 30-minute aerobic exercise programs per week in addition to a weekly half-hour group counseling session that focused on weight loss.  The control group did not amend their diet or exercise routines.

To assess physiological changes, researchers took high-resolution ultrasound images of the participant’s brains at baseline and again after the four month intervention to measure common carotid arteries.  Common carotid arteries are jugular arteries that supply oxygenated blood to the head and neck.  To measure any cognitive performance changes, study subjects were given several neurocognitive tests at baseline and again four months later to assess executive function, memory, and psychomotor speed.

Researchers found the DASH diet plus exercise group experienced significant improvements in neurocognitive function compared to the sedentary control group.  The DASH diet plus exercise group scored an impressive 6.1-year improvement on the four-month follow-up test that measured the time it took them to identify and differentiate colors and words from a list.  Conversely, the sedentary control group scored an 11.7-year poorer performance on the same test. Similar gains were found on the follow-up psychomotor speed test with both the DASH plus exercise and the DASH alone groups relative to the control group.  In addition, participants in both active treatment groups had lower blood pressure than the control group.

The biggest shortcoming of the Smith et al. study was it’s short four-month time frame. Researchers say they don’t know whether the benefits of the DASH diet plus exercise and DASH diet alone groups are temporary, or are things that can be maintained over time. The study does not reveal the underlying physiological mechanisms that improved cognitive function. Researchers also note that cognitive gains could be caused by a reduction in inflammation and other unknown neurochemical changes.

Both the DASH diet and the Mediterranean diet are very similar.  Both are based on heart-healthy eating habits that emphasize natural, unprocessed foods.  Both are rich in fruits and vegetables, whole grains, legumes and nuts.  Both diets encourage eating unsaturated fats, while saturated fats, sugar, and empty calories are strongly discouraged.  Both diets are also relatively flexible.  Finally, both promote long-term lifestyle changes rather than short-term fixes or dietary fads.

The main differences between the DASH diet and Mediterranean diet is that the DASH diet is more structured and emphasizes portion control and calorie restrictions, where as the Mediterranean diet doesn’t mention portion size or recommend specific amounts of any food group (Özkurt, 2015).  Both diets limit saturated fat intake, but the Mediterranean diet’s focus on olive oil means that it is more likely to be a high fat and calorie diet.  It’s also possible that the Mediterranean diet may be more heart-healthy due to the fact that it’s cholesterol-lowering properties.

Another important difference between the two diets is the DASH diet allows for two to four servings of dairy products each day.  Given the scarcity of dairy products in many parts of the Mediterranean region, many people following the Mediterranean diet can often go for days at a time without any dairy products.  And, while the DASH diet recommends daily lean red mean consumption, the Mediterranean diet mostly excludes red meat and recommends that some form of fish or seafood be eaten on a daily basis (Özkurt, 2015).

Given their many similarities, it’s not surprising several studies have conducted head-to-head comparisons of the DASH diet and Mediterranean diet.  Tangney et al. (2014), compared the two diets at how effective they were at slowing down cognitive decline in older adults.  826 older adults with an average age of 81.5 years were recruited for the prospective cohort study.

To help determine diet, participants filled out a self-report 144-item food frequency questionnaire at baseline.  They were also a cognitive assessment at baseline and at least two more over the four-year course of the study. Participants were assigned to three groups based on dietary scores monitoring how closely they adhered to either the DASH or Mediterranean diet.

Researchers then compared the DASH and Mediterranean groups relative rates of cognitive decline to a control group that followed a typical carbohydrate-rich diet.  The researchers found that both the DASH and Mediterranean dietary patterns resulted in slower rates of cognitive decline that were roughly the same.  Additionally, cognitive brain age testing scores for participants who followed the DASH diet the closest were at least 4.4 years younger than the group that followed it the least.  The study also found after the four-month intervention that learning and psychomotor function improved significantly for participants following the DASH dietary plan.  The researchers noted that findings from similar studies suggest that the cognitive benefits gained from the DASH diet may come quickly.

Researchers say they don’t know the underlying physiological reasons why the DASH and Mediterranean diet helped improved cognitive function, but they theorized that one main factor may be lower inflammation levels.  Reduced levels of inflammation have been found among people following both dietary patterns.  Inflammation is known to damage brain cells.  Also, the antioxidant protections provided by both the DASH diet and Mediterranean diet have been found to help protect against hypertension, obesity, diabetes, and cardiovascular disease.  Medical conditions that have all been linked to AD and cognitive decline.

Because the characteristics of both diets are so similar, Tangney et al. (2014), suggest the diets focus on natural, minimally processed foods and a reduced consumption of saturated fats may be more important than the specific diet type. Researchers said the findings point toward the need for more studies focusing on food-based approaches preventative and mitigating effects on cognitive decline. Researchers concluded by saying the stakes for finding out if diet can help prevent AD and vascular dementia have never been higher, considering the rapidly growing population of older adults at risk for the diseases.

Up next, a closer look at a brain-healthy diet that provides a significant cognitive boost even if you don’t follow all that closely.

Heller, M. (2016, April 4). What is the DASH diet? Retrieved from: http://dashdiet.org/ what_is_the_dash_diet.asp