Researchers working with mice bred to display autism-like behaviors found they could ease such behaviors with a low-glycemic (low sugar) diet – starting during the pregnancy of the animals' mothers.
The findings don’t prove that such a diet will help children with autism. But they back up anecdotal reports by many parents who say that autism symptoms improve when their children eat a less-sugary diet.
High-glycemic foods produce a rapid rise in blood sugar. They tend to be rich in simple carbohydrates such as sugar. Low-glycemic foods don’t produce such a blood-sugar spike. They include foods high in protein (nuts, beans and meat) and complex carbohydrates (whole grains and vegetables). Low-glycemic diets have long been recommended for people with diabetes, to help keep blood sugar on an even keel.
In their study, scientists at California’s Salk Institute used a strain of mice bred to display autism-like symptoms such as repetitive behaviors and social avoidance. Beginning in pregnancy, they divided the mice into two groups. One they fed a high-glycemic diet; the other, a low-glycemic diet. They kept the mouse pups on the same diet as their mothers’ after birth.
Though their diets differed, the two groups of mice consumed the same amount of calories and maintained similar weights. After the pups were weaned, the researchers used a battery of tests to assess their behaviors and brain development.
Less sugar, less symptoms
All the mice in the high-glycemic diet group showed all of the expected autism-like behaviors. They avoided contact with new mice placed near their chambers. They repeated actions that served no apparent purpose and groomed excessively.
By contrast, the mice in the low-glycemic group showed an overall reduction in their autism-like behaviors. They spent more time near new mice. They spent less time performing repetitive behaviors including excessive self-grooming.
Diet and brain development
The researchers went on to look for some of the autism-associated differences in brain development and biology that had been identified in studies with people.
Compared to the mice fed the low-glycemic diet, those on the high-glycemic diet had far lower brain levels of doublecortin – a protein associated with newly developing neurons (brain nerve cells). This difference was especially pronounced in a part of the brain that controls memory.
Diet and inflammation
In addition, the brains of the mice on the high-glycemic diet had greater numbers of activated microglia – the brain’s resident immune cells. (See image at top.) Their brains also showed more gene activity associated with inflammation.
The findings bolster those of earlier studies implicating inflammation during pregnancy with increased risk of autism in people. Most of those studies focused on inflammation from infection during pregnancy. However, studies have found that high-glycemic diets tend to produce chronic low-level inflammation in both people and laboratory animals. Some researchers have proposed that this is why diabetes during pregnancy increases the risk of autism in offspring. Indeed, the Salk researchers plan to see what happens when they give pregnant mice the high-glycemic diet but then feed their pups a normal or low-glycemic diet.
Diet and gut bacteria
The researchers also assessed whether a high-glycemic diet might influence the gut’s bacterial community, or “microbiome.” Previous studies have associated alterations in the microbiome with autism. They found chemical blood markers suggesting an increase in the levels of certain gut bacteria. The group plans further research to look more closely at these changes in gut bacteria and their relationship to the animals’ autism-like behaviors.
Putting the findings into perspective
“This study illustrates two of the broad themes that the best research on autism is pursuing,” comments developmental pediatrician Paul Wang, Autism Speaks head of medical research. (Dr. Wang was not involved in the study.) “First, it shows how genes and environment might interact. The mice have a genetic predisposition to autism-like symptoms, but changing their diet – an environmental factor – can improve their behavioral symptoms. Second, the study looks at how autism can affect many different systems in the body.”
Dr. Wang goes on to caution that benefits seen in animal models frequently fail to extend to people. While a low-glycemic diet is generally considered healthful, he strongly recommends that families work with a nutritionist before embarking on any kind of a restricted diet to ensure adequate nutrition. He notes concerns raised by recent research showing that serious nutrient imbalances are common among children with autism, even when they take nutritional supplements.
To learn more about the previous research mentioned in this story, also see: