A diet consisting of a high percentage of carbohydrates, particularly sugars, is associated with a higher risk of developing mild cognitive impairment (MCI) among people aged 70 and older, a study from the Mayo Clinic has found.
The study also found that consuming a higher percentage of protein and fat in relation to carbohydrates was associated with a lower risk of becoming cognitively impaired.
“I was surprised,” said lead author and Mayo epidemiologist Rosebud Roberts in a phone interview Tuesday. “I had originally thought the key thing [for an increased MCI risk] would be protein and fat, particularly protein.”
The study’s methods and findings
For the study, Roberts and her colleagues followed 937 people aged 70 to 89 for two-and-a-half to almost four years. Every 15 months, the participants were given a neurological evaluation and tested for full-blown dementia and MCI, a condition the Mayo Clinic defines as “problems with memory, language, thinking and judgment that are greater than normal age-related changes.” None exhibited signs of cognitive impairment at the start of the study.
Participants also filled out detailed questionnaires about their eating habits. The researchers used those questionnaires to calculate the amount of calories and macronutrients (carbohydrates, fats and protein) the participants were taking in daily.
At the end of the four years, Roberts and her colleagues found that the risk of MCI was almost twice as high among the quarter of the participants whose diets included the highest percentage of carbohydrates as it was among the quarter whose diets contained the lowest percentage. In addition, the more sugar in the diet (as opposed to other types of carbohydrates, like bread and pasta), the greater the risk.
Participants whose diets had the highest percentage of fat, on the other hand, were 42 percent less likely to develop cognitive impairment than those whose diets had the lowest percentage. And those with the highest intake of protein — compared to those with the lowest — had a reduced MCI risk of 21 percent.
In absolute numbers, 70 of the study’s participants in the quartile with the highest intake of carbohydrates had developed MCI by the end of the study compared to 36 in the lowest quartile. By contrast, 41 in the highest fat-intake quartile and 54 in the highest protein-intake quartile had developed MCI compared to 63 in the lowest quartiles for each of those categories.
An ‘optimal balance’
“These findings suggest that dietary patterns consisting of a high intake of energy derived from carbohydrates and a relatively low intake from fat and protein may have adverse implications for development of MCI,” the researchers write in the conclusion to their study. “In contrast, an optimal balance in the proportions of daily calories derived from carbohydrate, fat, and protein, may maintain neuronal integrity and optimal cognitive function in the elderly.”
What is that optimal balance of carbohydrates, fat and protein? Roberts said her study wasn’t designed to answer that question, but she noted that the people in her study who took in more than 58 percent of their daily calories from carbohydrates were at increased risk of developing MCI.
“Elderly people need to watch what they’re eating,” she said. “If you’re getting too much of one thing, it means you’re getting too little of another. It’s a relative thing. It’s not absolute.”
Interestingly, the participants in this study who consumed the most carbohydrates tended to have a lower body mass index (BMI) than those who ate the lowest amounts.
“Some of the relationships that we find in middle-aged people are different than what we find in older people,” explained Roberts. At mid-life, a high BMI is considered a risk factor for developing dementia at a later age, but “that’s not true with older people,” she said. “People who are on a trajectory to develop dementia tend to lose weight about 10 years before they actually develop it.”
The study has several limitations. To begin with, it was an observational study, which means it can show only a correlation between two things, not a cause-and-effect. Other factors in the participants’ lives, not yet identified, may explain the study’s results. In addition, participants self-reported their dietary habits, and people’s recall for such matters are not always accurate. Furthermore, the study’s participants were mostly white and, therefore, the findings may not be applicable to other populations.
In addition, the diagnosis of MCI is not without controversy. As I’ve reported here before, some experts believe that the cognitive symptoms that lead to an MCI diagnosis are just normal symptoms of aging and not necessarily an indicator of — or a precursor to — serious cognitive problems. Indeed, MCI symptoms often reverse themselves, and most people who are diagnosed with the condition do not go on to develop dementia.
Roberts said, however, that she’s persuaded that the best evidence suggests that people who are diagnosed with MCI are at an increased risk of dementia. “We’re trying to focus on ways to reduce that risk,” including eating a balanced diet, she added.
The Mayo Clinic study was funded by grants from the National Institutes of Health and the Robert H. and Clarice Smith and Abigail van Buren Alzheimer’s Disease Research Program. It was published recently in the Journal of Alzheimer’s Disease.