Highly Refined Carbs Boost Risk of Depression
Older women who consume large amounts of highly refined carbohydrates—such as sugar and flour—are at greater risk of developing new-onset depression, according to the results of research conducted at Columbia University Medical Center. Refined carbs are high glycemic index (GI) foods. They tend to cause sharp spikes in blood sugar levels, followed by sharp spikes in insulin levels. In contrast, the nutrients in low-GI foods tend to be absorbed much more slowly, which helps keep blood sugar levels steadier.
The study was based on data gathered from the National Institutes of Health's Women's Health Initiative Observational Study, conducted between 1994 and 1998. The group of women involved in the study were post-menopausal, meaning they had already gone through the “change of life”. None had previously been diagnosed with clinical depression. In essence, investigators found that post-menopausal women who consumed the greatest amounts of high-GI foods were significantly more likely to be diagnosed with depression.
The study probably indicates a link between wild oscillations in blood sugar and insulin levels and exacerbations in mood, fatigue, and other signs of depression. In contrast, women who consumed greater amounts of dietary fiber, whole grains, vegetables and non-juice fruits experienced a decreased risk of depression.
Previous, unrelated studies have concluded that the kinds of foods we eat can have a significant impact on the health and diversity of the communities of friendly bacteria (the microbiome) living in the digestive tract. And it’s already been established that the microbiome influences mood. Not surprisingly, microbes associated with better mood tend to prefer high-fiber foods.
"Our diets have a huge impact on microbial populations in the gut," says Carlo Maley, PhD, director of the UCSF Center for Evolution and Cancer. "It's a whole ecosystem, and it's evolving on the time scale of minutes.” Research suggests that gut bacteria may affect our behavior, including decisions about what to eat, in part by acting through the vagus nerve. This major cranial nerve connects 100 million nerve cells from the digestive tract to the base of the brain.
"Microbes have the capacity to manipulate behavior and mood through altering the neural signals in the vagus nerve, changing taste receptors, producing toxins to make us feel bad, and releasing chemical rewards to make us feel good," says Athena Aktipis, PhD, who is currently in the Arizona State University Department of Psychology.
Ironically, many women—and men, too—reach for sugary treats, or salty refined-carbohydtate-type snacks when they’re feeling tired or down. But that’s likely to make things worse, not better. Next time you need a pick-me-up, think fresh fruit or carrot sticks instead, perhaps.
Joe Alcock, Carlo C. Maley, C. Athena Aktipis. Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. BioEssays, 2014; DOI: 10.1002/bies.201400071
James Gangwisch, PhD et al. High Glycemic Index Diet as a Risk Factor for Depression: Analyses from the Women’s Health Initiative. American Journal of Clinical Nutrition, August 2015
Kavli Foundation. "Could gut microbes help treat brain disorders? Mounting research tightens their connection with the brain." ScienceDaily. ScienceDaily, 8 January 2015. .