There’s no question that Alzheimer’s is one of the most feared age-related diseases. Even mild cognitive decline such as forgetting someone’s name or where you put the car keys can put you on alert.
So it’s not surprising that there has been a flurry of research over the years looking at Alzheimer’s and memory. Scientists have looked at everything from supplements and prescription medication to diet and exercise.
When it comes to the latter two lifestyle issues, researchers have found that a more Western-style diet, also called a Standard American Diet (SAD), which includes saturated fats, refined carbohydrates and excess sugar, has been associated with an increased risk of both cognitive impairment and Alzheimer’s disease. On the flip side, a more Mediterranean-style diet rich in omega-3 fatty acids and fiber and low in refined carbs has been linked to a decreased risk of these conditions.
When it comes to exercise, research has clearly shown that it is extremely protective of your brain, in terms of brain volume and neural connections, as well as cognitive impairment and reducing your risk of Alzheimer’s disease.
But what about the combination? Does a good diet paired with exercise give you a super boost? What if you have a poor diet? Can exercise offset your chances of suffering from dementia? Let’s find out!
Can You Out-Exercise a Bad Diet?
Having explored the effects of diet on several brain biomarkers, Seattle researchers questioned if high-intensity exercise could impact the beneficial or damaging effects of diet on cognitive function.
To test this, they divided 41 adults with an average age of 68 into two groups. The first group consisted of 18 adults with normal cognitive function, while the second group of 23 adults had mild cognitive impairment.
All participants were tested before and after the study period for a number of cognitive biomarkers, including:
- Amyloid-beta (high levels are associated with Alzheimer’s disease)
- Tau protein (neural proteins that, when defective, can lead to dementia)
- Glucose tolerance/insulin sensitivity
- Visuospatial memory test (to determine cognitive function)
Next, participants filled out a seven-day questionnaire to assess their level of physical activity before the study period. They were asked to describe the type and level of activity they did on a daily basis. They also noted the duration of the activity, whether their heart rate increased, and whether their breathing changed.
The activity was then categorized as either low intensity or high intensity. Low intensity indicated activities such as casual walking, light gardening, or stretches that didn’t raise the heart rate and allowed for normal breathing. High-intensity activities were things like jogging, biking or an aerobics class in which the heart rate became elevated and breathing was more labored.
Finally, researchers divided each of the two groups in half (for a total of four groups). Half of the “normal” group ate a low-glycemic diet (good) for four weeks, while the other half consumed a high-glycemic diet (bad). Researcher similarly divided the group with mild cognitive impairment, giving half of them a low-glycemic diet for four weeks while the other half ate a high-glycemic diet.
At the end of the four weeks, researchers found that exercise does more than a body good. It’s good for your brain as well.
Exercise Protects Against a SAD Diet
Researchers found that when people in the “normal” group ate the high-glycemic diet, they had higher amyloid-beta, as well as delayed recall on the memory test. Conversely, when those in this group ate the low-glycemic diet, they not only had lower levels of amyloid-beta, but they also had improved memory test scores.
But where it got interesting was when you factored in pre-study levels of high-intensity exercise. Researchers found that the longer the duration of the exercise, the greater the impact.
In the “normal” group, there was a slight improvement in amyloid-beta levels in those who ate the low-glycemic diet but exercised more. However, those who ate the high-glycemic diet but logged more exercise time had significantly lower amyloid-beta levels.
In the group with mild cognitive impairment, the benefits of exercise were a bit complicated. As you would expect, those who at the high-glycemic diet but indicted a greater amount of exercise had significantly lower levels of amyloid-beta.
But, in the low-glycemic group, the results were surprising. In that group, increased exercise was associated with a significant increase in amyloid-beta. Now here’s the really strange part. Researchers said that the higher level of exercise “potentiated” or enhanced the beneficial effects of the low-glycemic diet. But, according to the figure in the study, that is not accurate. That is a significant flaw with the study and one that needs to be addressed.
When it came to tau protein, more exercise in the “normal” groups was associated with lower tau levels. However, in the mild impairment groups, there was no decrease in tau, regardless of exercise status.
The opposite was found when it came to insulin sensitivity. Those in the normal group saw no significant change, regardless of activity levels. But those with mild cognitive decline saw insulin levels decrease as exercise increased.
Given the results, researchers concluded, “Exercise may offset the potential pathological effects of a Western-type diet on [Alzheimer’s disease] biomarkers in the brain” for people with normal cognitive function.
That is, exercise help offset a bad diet, but only in those people who don’t show signs of cognitive decline.
They go on to say that, in those people with early signs of dementia or mild impairment, the “maximum” effect can only be achieved through a combination of a low-glycemic diet and frequent, high-intensity exercise.
Lastly, they do acknowledge several limitations with their study. First and foremost is the sample size. They also point to the use of the self-reported questionnaire to determine activity level. Additionally, they suggest that future testing may want to use additional biomarkers other than amyloid-beta and tau protein to indicate risk of Alzheimer’s disease.
Prevention is Key
So, what’s the takeaway? Despite the pretty major question regarding mild impairment and the low-glycemic diet, it seems quite clear that an ounce of prevention is worth a pound of cure.
Don’t wait to institute healthy habits. Load your plate with lean proteins, ideally fish or legumes; colorful fruits and vegetables; and whole grains. Keep sugar and refined carbohydrates to a minimum, and think omega-3 fats versus saturated fats.
And get moving! Regardless of whether you run, bike, swim, dance or play a sport, just get out there and move your body at least five days a week for 30 to 60 minutes a day.
 Kanoski, SE and Davidson, TL. Western diet consumption and cognitive impairment: Links to hippocampal dysfunction and obesity. Physiol Behav. 2010;103:59-68.
 Feart, C et al. Adherence to a Mediterranean diet, cognitive decline, and risk of dementia. JAMA. 2009;302:638-48.
 Graff-Radford, NR. Can aerobic exercise protect against dementia? Alzheimers Res Ther. 2011;3:6.
 Larson, EB et al. Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older. Ann Intern Med. 2006;144:73-81.
 Baker, LD et al. High-intensity physical activity modulates diet effects on cerebrospinal amyloid-B levels in normal aging and mild cognitive impairment. J Alzheimers Dis. 2011 Oct 4. [Epub ahead of print.]