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Sugar on the Brain

How the sweet stuff may affect learning and memory

   

We all know what sugar can do to our waistlines. And our teeth. But what about our brains? Does a diet high in sugary food and drinks take a toll on our memory and smarts as we age?

Or, as a number of news articles about sugar research bluntly put it: Can sugar make you stupid?

Granted, that’s a bit harsh. No one’s talking about a decline in thinking skills from having an occasional dessert or sweet treat. But a growing number of studies have suggested that high sugar consumption seems to affect the brain and alter its ability to learn and remember information.

This shouldn’t be too surprising, considering the amount of previous research showing that regularly eating too much sugar may harm the body in different ways. It has been linked to obesity as well as to increased risk for type 2 diabetes, heart disease and liver disease. Diabetes, especially when blood sugar levels are not controlled, is also considered a risk for dementia.

Because of the health risks linked to sugar, a federal advisory committee on the upcoming 2020–2025 new dietary guidelines is recommending that Americans limit their consumption of added sugars to 6 percent of their daily calories, down from the current recommendation of 10 percent. This refers to sugar that is added to food — such as in cookies and soft drinks — not sugar that occurs naturally.

Still, whether too much sugar contributes to mental decline or dementia remains a hotly debated topic because these are complex conditions, affected by genetic, health and dietary factors, all of which are interrelated.

In addition, many sugar studies have been done on animals, not people. Scientists say these animals provide a reasonable approximation of human physiology, and observing the changes in their brains can help researchers understand the basics of sugar’s effects on human brain activity.

It also allows for research into the differences between types of sugar, comparing the brain effects of fructose with sucrose and glucose.

In our diet, sugar comes from different sources and, in some cases, two types of sugar can even show up in one type of food. Fructose is generally found in fresh fruits and some vegetables like apples, pears and peas, although it also can be processed into a sweetener for not-so-healthy foods like soda. Sucrose — a combo of fructose and glucose that becomes table sugar — is typically the refined, added sugar in baked goods, ice cream and candy. Glucose is a simple sugar often found in tandem with fructose in dried fruit, honey, sweet corn and fruit juices.

All three of these types of sugar are similar, but they differ in the way they are digested and used by the body and the brain. For example, glucose is mainly processed in the small intestine and sent to the cells to be stored for energy, while fructose is metabolized and mainly stored in the liver.

“Animals fed a high concentration of fructose is comparable to people who have been heavy drinkers of soda for a long time. We think these studies show that too much fructose may harm the brain as well as the body,” said Fernando Gomez-Pinilla, professor and director of the Neurotrophic Research Laboratory at the University of California, Los Angeles, who has been studying sugar’s effects on the brains of animals for about two decades.

In a 2016 study, Gomez-Pinilla and a team of researchers found that a high-fructose diet hampered learning and memory in rats, but that giving them omega-3 fatty acids (typically found in foods like fish, nuts and flaxseed) counteracted some of these negative effects.

In the study, the rats were trained to successfully make their way through a maze. They then were given a fructose solution to drink, along with their regular food, for six weeks. One group was also given omega-3 supplementation in addition to the fructose. After six weeks, the rats were tested on their ability to remember the correct route to escape the maze.

The fructose group was markedly slower and had trouble recalling the route, suggesting the fructose had affected their memory. They also had “significantly increased” levels of blood glucose, triglycerides and insulin, all indicators of metabolic disorders, researchers found.

By comparison, the fructose-with-omega-3 group was twice as fast at remembering the correct route out of the maze — close to that of the control group, which had been given neither fructose nor omega-3s. The omega-3 group also had significantly better levels of triglycerides and insulin than the fructose group.

“What this shows is that it’s important to combine many types of food in our diet. If we have a healthy base diet — especially if we eat a lot of foods with omega-3s plus other healthy things like vegetables — we have the freedom once in a while to have some sugar,” Gomez-Pinilla said.

More recently, a Danish study published in November 2019 in the journal Scientific Reports found that just 12 days of drinking a sugar solution for an hour a day caused major changes in the reward system in the brains of mini-pigs, which have a large, complex brain and metabolism similar to humans. The changes, seen on brain scans of the animals, were “similar to those observed when addictive drugs are consumed,” researchers reported.

But what about sugar’s effect on the human brain? Study results in animals do not always translate to humans. Although fewer studies have been done on humans, a 2013 Yale study published in JAMA, used brain imaging to reproduce in people what had been observed in rats: that the brain responds differently depending on the type of sugar consumed. 

Researchers measured the blood flow to the brain in 20 healthy adults to see how their brains responded to both fructose and glucose. Glucose is better than fructose at prompting the body to release the hormone insulin, which acts in the brain to keep a person from overeating. Fructose does a weak job at stimulating insulin, so there’s only a weak message from the brain to stop eating. That’s why in mice studies, those given fructose ate more than those given glucose.

Similarly, in the Yale study, subjects said they felt fuller and more satisfied after the glucose drink and their brain scans also showed glucose was better at triggering appetite control and turning off reward regions of the brain than fructose.

Among older adults, a 2019 study in the journal Clinical Interventions in Aging, found that eating lots of sugar was linked to lower scores on learning and memory tests — but there was one bit of good news.

The study looked at the association between sugar intake and cognitive decline among 1,200 Malaysian adults ages 60 and older.

Sugar consumption is widespread and rapidly increasing in Malaysia, researchers with the Universiti Kebangsaan Malaysia wrote, rising by 91 percent between 1963 and 2013, thanks to the greater availability of sweetened beverages, processed foods and desserts. This has been accompanied by an increase in the prevalence of obesity and type 2 diabetes.

In the study, subjects were given six cognitive tests to assess their learning and memory skills, and were interviewed about what they had eaten at each meal for the past week.

The findings showed that a high consumption of sugary beverages, cakes and desserts was significantly associated with a greater risk for cognitive impairment.

The one bright spot: Those whose sugar came primarily from cooked dishes and naturally sweet fruits had better cognitive function and higher performance on the mental skills tests.

The cooked dishes, researchers noted, may have had some sugar, but they also were a source of other nutrients important for cognitive function, thereby “neutralizing the detrimental effect of the sugar.”

What you need to know:

Cut back on sugary drinks. For most Americans, the most common source for added sugar is beverages, including soda, fruit drinks, sports drinks and sugary coffee and tea drinks. These drinks account for almost half (47 percent) of all added sugars consumed by Americans age 2 and older, according to the 2015–2020 U.S. Dietary Guidelines report. We get about 17 teaspoons of sugar daily just from added sugar in our food and drinks.

Aim for fructose from real fruit. Fructose is a sugar found naturally in fruit, but there’s a difference between the fructose you get eating an apple or blueberries and the fructose you get as a processed sweetener in soda or other drinks. Fructose in fresh fruit comes with “fiber, antioxidants and flavonoids and that combination of nutrients is better for our brain,” Gomez-Pinilla says.

Make the sugar switch. You don’t have to give up everything sweet. You just need to make some healthy shifts in the sugar you choose. Check out these simple tips for cutting down on added sugars from the Dietary Guidelines for Americans 2015–2020. —Candy Sagon

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Membership Expires: Renew

Sugar on the Brain

How the sweet stuff may affect learning and memory

   

We all know what sugar can do to our waistlines. And our teeth. But what about our brains? Does a diet high in sugary food and drinks take a toll on our memory and smarts as we age?

Or, as a number of news articles about sugar research bluntly put it: Can sugar make you stupid?

Granted, that’s a bit harsh. No one’s talking about a decline in thinking skills from having an occasional dessert or sweet treat. But a growing number of studies have suggested that high sugar consumption seems to affect the brain and alter its ability to learn and remember information.

This shouldn’t be too surprising, considering the amount of previous research showing that regularly eating too much sugar may harm the body in different ways. It has been linked to obesity as well as to increased risk for type 2 diabetes, heart disease and liver disease. Diabetes, especially when blood sugar levels are not controlled, is also considered a risk for dementia.

Because of the health risks linked to sugar, a federal advisory committee on the upcoming 2020–2025 new dietary guidelines is recommending that Americans limit their consumption of added sugars to 6 percent of their daily calories, down from the current recommendation of 10 percent. This refers to sugar that is added to food — such as in cookies and soft drinks — not sugar that occurs naturally.

Still, whether too much sugar contributes to mental decline or dementia remains a hotly debated topic because these are complex conditions, affected by genetic, health and dietary factors, all of which are interrelated.

In addition, many sugar studies have been done on animals, not people. Scientists say these animals provide a reasonable approximation of human physiology, and observing the changes in their brains can help researchers understand the basics of sugar’s effects on human brain activity.

It also allows for research into the differences between types of sugar, comparing the brain effects of fructose with sucrose and glucose.

In our diet, sugar comes from different sources and, in some cases, two types of sugar can even show up in one type of food. Fructose is generally found in fresh fruits and some vegetables like apples, pears and peas, although it also can be processed into a sweetener for not-so-healthy foods like soda. Sucrose — a combo of fructose and glucose that becomes table sugar — is typically the refined, added sugar in baked goods, ice cream and candy. Glucose is a simple sugar often found in tandem with fructose in dried fruit, honey, sweet corn and fruit juices.

All three of these types of sugar are similar, but they differ in the way they are digested and used by the body and the brain. For example, glucose is mainly processed in the small intestine and sent to the cells to be stored for energy, while fructose is metabolized and mainly stored in the liver.

“Animals fed a high concentration of fructose is comparable to people who have been heavy drinkers of soda for a long time. We think these studies show that too much fructose may harm the brain as well as the body,” said Fernando Gomez-Pinilla, professor and director of the Neurotrophic Research Laboratory at the University of California, Los Angeles, who has been studying sugar’s effects on the brains of animals for about two decades.

In a 2016 study, Gomez-Pinilla and a team of researchers found that a high-fructose diet hampered learning and memory in rats, but that giving them omega-3 fatty acids (typically found in foods like fish, nuts and flaxseed) counteracted some of these negative effects.

In the study, the rats were trained to successfully make their way through a maze. They then were given a fructose solution to drink, along with their regular food, for six weeks. One group was also given omega-3 supplementation in addition to the fructose. After six weeks, the rats were tested on their ability to remember the correct route to escape the maze.

The fructose group was markedly slower and had trouble recalling the route, suggesting the fructose had affected their memory. They also had “significantly increased” levels of blood glucose, triglycerides and insulin, all indicators of metabolic disorders, researchers found.

By comparison, the fructose-with-omega-3 group was twice as fast at remembering the correct route out of the maze — close to that of the control group, which had been given neither fructose nor omega-3s. The omega-3 group also had significantly better levels of triglycerides and insulin than the fructose group.

“What this shows is that it’s important to combine many types of food in our diet. If we have a healthy base diet — especially if we eat a lot of foods with omega-3s plus other healthy things like vegetables — we have the freedom once in a while to have some sugar,” Gomez-Pinilla said.

More recently, a Danish study published in November 2019 in the journal Scientific Reports found that just 12 days of drinking a sugar solution for an hour a day caused major changes in the reward system in the brains of mini-pigs, which have a large, complex brain and metabolism similar to humans. The changes, seen on brain scans of the animals, were “similar to those observed when addictive drugs are consumed,” researchers reported.

But what about sugar’s effect on the human brain? Study results in animals do not always translate to humans. Although fewer studies have been done on humans, a 2013 Yale study published in JAMA, used brain imaging to reproduce in people what had been observed in rats: that the brain responds differently depending on the type of sugar consumed. 

Researchers measured the blood flow to the brain in 20 healthy adults to see how their brains responded to both fructose and glucose. Glucose is better than fructose at prompting the body to release the hormone insulin, which acts in the brain to keep a person from overeating. Fructose does a weak job at stimulating insulin, so there’s only a weak message from the brain to stop eating. That’s why in mice studies, those given fructose ate more than those given glucose.

Similarly, in the Yale study, subjects said they felt fuller and more satisfied after the glucose drink and their brain scans also showed glucose was better at triggering appetite control and turning off reward regions of the brain than fructose.

Among older adults, a 2019 study in the journal Clinical Interventions in Aging, found that eating lots of sugar was linked to lower scores on learning and memory tests — but there was one bit of good news.

The study looked at the association between sugar intake and cognitive decline among 1,200 Malaysian adults ages 60 and older.

Sugar consumption is widespread and rapidly increasing in Malaysia, researchers with the Universiti Kebangsaan Malaysia wrote, rising by 91 percent between 1963 and 2013, thanks to the greater availability of sweetened beverages, processed foods and desserts. This has been accompanied by an increase in the prevalence of obesity and type 2 diabetes.

In the study, subjects were given six cognitive tests to assess their learning and memory skills, and were interviewed about what they had eaten at each meal for the past week.

The findings showed that a high consumption of sugary beverages, cakes and desserts was significantly associated with a greater risk for cognitive impairment.

The one bright spot: Those whose sugar came primarily from cooked dishes and naturally sweet fruits had better cognitive function and higher performance on the mental skills tests.

The cooked dishes, researchers noted, may have had some sugar, but they also were a source of other nutrients important for cognitive function, thereby “neutralizing the detrimental effect of the sugar.”

What you need to know:

Cut back on sugary drinks. For most Americans, the most common source for added sugar is beverages, including soda, fruit drinks, sports drinks and sugary coffee and tea drinks. These drinks account for almost half (47 percent) of all added sugars consumed by Americans age 2 and older, according to the 2015–2020 U.S. Dietary Guidelines report. We get about 17 teaspoons of sugar daily just from added sugar in our food and drinks.

Aim for fructose from real fruit. Fructose is a sugar found naturally in fruit, but there’s a difference between the fructose you get eating an apple or blueberries and the fructose you get as a processed sweetener in soda or other drinks. Fructose in fresh fruit comes with “fiber, antioxidants and flavonoids and that combination of nutrients is better for our brain,” Gomez-Pinilla says.

Make the sugar switch. You don’t have to give up everything sweet. You just need to make some healthy shifts in the sugar you choose. Check out these simple tips for cutting down on added sugars from the Dietary Guidelines for Americans 2015–2020. —Candy Sagon