What questions did you and your colleagues ask yourselves as you analyzed the information from the questionnaires, the brain scans and the cognitive tests?
Basically, what is the mechanism of action? How does increased caloric intake lead to cognitive impairment? We don't know this, but there are other researchers who have done work in this area. Mark Mattson at the Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center in Baltimore in 2000 published a study with a very catchy title, "Take Away My Food and Let Me Run," indicating that excessive caloric intake may lead to oxidative stress within the cell and that may lead to damage. On the other hand, based on animal studies, a 30 percent caloric restriction seems to stimulate neuroprotective factors that can increase the resistance of neurons in the brain to dysfunction and death.
What other research has influenced your study?
I became curious when I read in 2009 that caloric restriction in monkeys was associated with less mortality and improved cognitive function. That study was done by investigators at the Wisconsin National Primate Research Center. There were many other similar studies before 2009 involving monkeys, rodents and worms as well. Our research is also consistent with a group of Australian National University researchers conducting The Personality and Total Health (PATH) Through Life Project. [In a paper published in September 2011 in the American Journal of Geriatric Psychiatry, the PATH researchers found that excessive caloric intake and high intake of monounsaturated fats was predictive of mild cognitive impairment.]
What do you have planned for future study of caloric intake and memory loss?
In this particular study we did not adjust for physical exercise. I think we are going to do that as well as look at the macronutrients, such as carbohydrates and proteins, to see which ones might be of concern. This time we considered how much participants ate but did not take into account what they ate.
Why didn't you include data about what patients ate in addition to how much they ate?
We have data about what they ate, but for this analysis I only looked at the total calories. This was the first thing we wanted to see. Once you get the signal, you keep probing. There are many more dimensions we will get from the questionnaire data.
People should be very, very careful not to overstretch our findings at this point. Certainly people should not look at those three categories and say, 'Well, if I consume less than 1,500 calories, then I will not have MCI.' That would be the wrong conclusion. Instead, they should combine all that they know about diet from their doctors and add to that the issue of consuming too many calories. In addition to being bad for your heart, it might be bad for your brain as well. People should consider everything they know about healthy lifestyle and add this into the mix as well. Certainly we are not recommending starvation or malnutrition.