The title is a short version of the concluding sentence from a new Mayo Clinic study. The study tracked 937 initially healthy people aged 70-89 for 3.7 years. During this period 200 developed mild cognitive impairment (MCI) or dementia.
Those patients who were in the highest quartile (i.e. a group) of carbohydrate consumption (as percentage of total calories), have had approximately twice the risk of MCI or dementia (1.89 times, confidence interval P for trend =0.004(*)). Those who belonged to the highest quartile of fat consumption had about one-half the risk of developing MCI or dementia (0.56, P for trend = 0.03(**)). Those with the highest protein intake had 21% lower risk.
The fact that fat, especially saturated seems to be beneficial in dementia and other neurological degenerative diseases, has been known for some time, see for example the references in my past posts: this or this
This study however, is probably one of the first, if not the first, to concentrate on all three macronutrients' intake rather than some partial aspects of the diet.
A dietary pattern with relatively high caloric intake from carbohydrates and low caloric intake from fat and proteins may increase the risk of MCI or dementia in elderly persons.
Although the full text is pay-walled, a short writeup is posted on the Mayo Clinic website.
Interestingly, a comparison between the highest quartile of total carbohydrates with the highest sugar (see the quote below), shows that the sugar impact was negative but not to the same extent as the total carbohydrate. This may be indicating that some other form of cabohydrate than the sugar alone, may be the most detrimental to the neurological health. Perhaps the total starch [ *** WHEAT?! ***] or just the total glycemic load?
Those who reported the highest carbohydrate intake at the beginning of the study were 1.9 times likelier to develop mild cognitive impairment than those with the lowest intake of carbohydrates. Participants with the highest sugar intake were 1.5 times likelier to experience mild cognitive impairment than those with the lowest levels.
But those whose diets were highest in fat - compared to the lowest - were 42 percent less likely to face cognitive impairment, and those who had the highest intake of protein had a reduced risk of 21 percent.
When total fat and protein intake were taken into account, people with the highest carbohydrate intake were 3.6 times likelier to develop mild cognitive impairment.
"A high carbohydrate intake could be bad for you because carbohydrates impact your glucose and insulin metabolism," Dr. Roberts says. "Sugar fuels the brain - so moderate intake is good. However, high levels of sugar may actually prevent the brain from using the sugar - similar to what we see with type 2 diabetes."
(*) It means that the probability of the result being by chance is 1/250.
(**) Probability of the result being by chance is 1/33.
(***) Added 13/01/2013, inspired by this .
(I am grateful and indebted to the best source of alerts about new interesting nutrition studies - vegan discussion groups! Oh my oh my... Thank you drmcdougall.com )