By Pat Anson, PNN Editor

For many of us, the holiday season wouldn’t be complete without Christmas cookies, jelly donuts, plum pudding, chocolate babka, or even the much-maligned fruit cake.

But if you're prone to depression or have an inflammatory condition, you might want to avoid those sweet treats. Or at least enjoy them in moderation.

New research by clinical psychologists at the University of Kansas suggests that dietary sugars found in many holiday foods can trigger metabolic, inflammatory and neurobiological processes that can lead to insomnia, digestive problems and depression – which all enhance physical pain.

"A large subset of people with depression have high levels of systemic inflammation,” said lead author Stephen Ilardi, PhD, an associate professor of clinical psychology at KU. "When we think about inflammatory disease we think about things like diabetes and rheumatoid arthritis - diseases with a high level of systemic inflammation. We don't normally think about depression being in that category, but it turns out that it really is.

“We also know that inflammatory hormones can directly push the brain into a state of severe depression. So, an inflamed brain is typically a depressed brain. And added sugars have a pro-inflammatory effect on the body and brain."

Depression Causes Sugar Cravings

Dwindling daylight in winter can worsen depression and prompt people to consume more sweets, which provide a temporary emotional lift.

"One common characteristic of winter-onset depression is craving sugar," Ilardi said. "So, we've got up to 30% of the population suffering from at least some symptoms of winter-onset depression, causing them to crave carbs - and now they're constantly confronted with holiday sweets.

"When we consume sweets, they act like a drug. They have an immediate mood-elevating effect, but in high doses they can also have a paradoxical, pernicious longer-term consequence of making mood worse, reducing well-being, elevating inflammation and causing weight gain."

The KU research team analyzed a wide range of studies on the physiological and psychological effects of sugar, including the Women's Health Initiative study, the NIH-AARP Diet and Health Study, and studies of Australian and Chinese soda-drinkers. Their research is published in the journal of Medical Hypotheses.

Ilardi says consuming high amounts of sugar could be as physically and psychologically harmful as drinking too much liquor.

"We have pretty good evidence that one alcoholic drink a day is safe, and it might have beneficial effect for some people," Ilardi said. "Alcohol is basically pure calories, pure energy, non-nutritive and super toxic at high doses. Sugars are very similar."

The average American gets about 14% of their calories from added sugars – the equivalent of 18 teaspoons of sugar each day. Most people know a high-sugar diet can lead to diabetes, obesity and cardiovascular problems.

Another way to look at sugar is to think of it as fuel for bacteria.  

"Our bodies host over 10 trillion microbes and many of them know how to hack into the brain," Ilardi said. "The symbiotic microbial species, the beneficial microbes, basically hack the brain to enhance our well-being. They want us to thrive so they can thrive.

“But there are also some opportunistic species that can be thought of as more purely parasitic - they don't have our best interest in mind at all. Many of those parasitic microbes thrive on added sugars, and they can produce chemicals that push the brain in a state of anxiety and stress and depression. They're also highly inflammatory."

Ilardi recommends eating a minimally processed diet rich in fruits, vegetables, fish and whole grains, while avoiding red meats, refined grains, fructose and other unhealthy foods. As for sugar, the KU researcher urges moderation -- not just during the holidays, but year-round.