Researchers have found that there's a part of your body that might actually shrink when you eat too much fast food.
Unfortunately, it's your brain.
People with diets high in trans fats are more likely to experience the kind of brain shrinkage associated with Alzheimer's disease than people who consume less of the artery-damaging fats, the new study suggests.
Those with diets high in vitamins C and E, the B vitamins and vitamin D, meanwhile, appear to have larger brains than people with diets low in these nutrients.
And diets high in omega 3 fatty acids seemed to benefit the small blood vessels of the brain — "and the thinking abilities related to those vessels," said lead investigator Dr. Gene Bowman.
The work — published in the journal Neurology — involved 104 people, ages 65 and older, enrolled in the Oregon Brain Aging Study. All were generally healthy elders, with few smokers or people with diabetes or high blood cholesterol.
When the study was launched in 1989, "the aim was to study the effects of age on dementia risk in people that don't have factors known to increase their risk at the time," Bowman said.
Other researchers have linked diet and dementia. But the usual strategy is to have people fill out questionnaires about the type and frequency of foods they eat — except people sometimes forget. Age can also affect how the body absorbs nutrients.
In the new study, researchers checked blood samples for markers of 30 different nutrients. Participants also did a raft of neuropsychological tests, and 42 had MRI scans of their brains as well. The team was interested in three things: cognitive function, total brain volume and white matter changes thought to be a sign of small vessel disease of the brain.
Small vessel disease, also known as cerebral small vessel disease, is an accumulation of plaque deposits in the small blood vessels throughout the brain. It can lead to stroke.
"We know in Alzheimer's disease that total brain atrophy (or shrinkage) is accelerated compared to people of the same age and same gender that don't have Alzheimer's disease," said Bowman, a naturopathic doctor in the department of neurology at the Oregon Health and Science University in Portland.
Among the key findings:
- The B vitamins, the antioxidants C and E and vitamin D all seemed to be working in concert in some way the researchers can't yet fully explain. But the B-C-E-D pattern was associated with greater total brain volume and better global cognitive function. People who scored low on this vitamin combination turned out to have less total brain tissue;
- People who had high levels of circulating trans fats had less brain volume. They also had poorer memory, attention, language and processing speed skills;
- People with higher levels of omega 3 fatty acids had better executive function — the ability to plan, problem solve, multi-task and perform other functions — as well as fewer white matter lesions on their brain scans.
The findings held after researchers took age, sex, education, hypertension and genetic and other factors into account.
Some trans fats are found naturally, in small amounts, in dairy products, beef and lamb, but the trans fats in the study are hidden in cakes, flaky pastries, potato chips and other fried, frozen and processed food.
Trans fatty acids increase inflammation, make arteries harder and decrease heart rhythm, increasing the risk of cardiac arrest.
But only a handful of studies have looked at the relationship between trans fats and brain function, Bowman said. "I think our study is one of the first to look at blood levels of trans fats related to brain health."
He said the term "brain shrinkage" is a bit of a misnomer, because the researchers didn't look at rates of change over time. And the study doesn't prove cause-and-effect, just an association.
But evidence suggests that trans fats can replace good fats in cell membranes, "and when that occurs it changes the structure and chemical properties of the cell in an unfavourable way," Bowman said.
"Trans fats are known to be bad for cardiovascular health," he said. "It makes sense that they're probably bad for the brain, too."
He recommended avoiding processed foods that list "partially hydrogenated oils" on the ingredient list. "That's trans fat," Bowman said.