When it comes to sugar, we don’t have a sweet understanding.
I’m sure you are as confused as I when you read contradictory advice like:
- Sugar is sugar, and there’s no difference in how your body digests the various forms.
- Fructose (sugar from fruit) is healthy, while sucrose (processed sugar) creates problems.
- Your body regards high fructose corn syrup the same as any other sugar.
- Your body processes fructose and sucrose the same way and cannot tell the difference.
After a while, these statements become mind-boggling. How can something as healthy-sounding as natural sugar (fructose) not be better for you than processed sugar (sucrose)?
Well, there is a difference; and it just may surprise you.
It is true that fructose and sucrose are both sugars and both are carbohydrates. But fructose is a monosaccharide, or simple sugar, the basic unit of a carbohydrate molecule. Sucrose is a polysaccharide, or a long carbohydrate molecule that is formed when monosaccharides link.
While fructose and sucrose taste sweet and are both commonly found in the foods we eat, they have different chemical properties. Fructose is most often consumed from the fruit we eat, which is the reason it is often called fruit sugar. Sucrose, on the other hand, is the white crystal sugar we buy and consume: table sugar.
Your body does not need to break down fructose before it is absorbed via the intestines. However, your body needs a digestive enzyme called sucrase to digest, or break down, sucrose. Because of their contrasting chemical makeups, fructose does not require the body to produce as heavy an insulin release as it needs for sucrose. Sucrose signals the pancreas to release insulin as a message to the body’s cells to absorb blood sugar.
You might assume that because fructose is natural and does not require as much of an insulin response, it is a healthier nutrient than sucrose and that fruit sugar is better for you than table sugar. I believed this for many decades. However, a recent study at Yale University, published in the Journal of the American Medical Association (JAMA), indicates otherwise. When researchers studied neurophysiological factors that may underlie associations between fructose consumption and weight gain, they found that fructose is more likely associated with obesity than sucrose.
Fructose And Glucose
The researchers at Yale titled their report “Effects of fructose vs glucose on regional cerebral blood flow in brain regions involved with appetite and reward pathways.” For the study, 20 healthy adults underwent two MRI sessions at Yale. Each imaging session followed consumption of either a fructose-sweetened or a glucose-sweetened beverage. Participants did not know which sweetener was in their beverage. The study was conducted with a blinded, random-order, crossover design.
The researchers measured the changes in hypothalamic regional cerebral blood flow (CBF) after consumption of each drink. A secondary analysis focused on whole-brain analyses to “explore regional CBF changes, functional connectivity analysis to investigate correlations between the hypothalamus and other brain region responses, and hormone responses to fructose and glucose ingestion.”
The study findings were unexpected. (This is a bit technical, but I explain below.):
- There was a significantly greater reduction in hypothalamic CBF after glucose versus fructose ingestion.
- Glucose ingestion (compared with baseline) increased functional connectivity between the hypothalamus and the thalamus and striatum.
- Fructose increased connectivity between the hypothalamus and thalamus but not the striatum.
- Regional CBF within the hypothalamus, thalamus, insula, anterior cingulate and striatum (appetite and reward regions) was reduced after glucose ingestion compared with baseline.
- In contrast, fructose reduced regional CBF in the thalamus, hippocampus, posterior cingulate cortex, fusiform and visual cortex.
- In whole-brain voxel-level analyses, there were no significant differences between direct comparisons of fructose versus glucose sessions following correction for multiple comparisons.
What That Means
I know the results of the Yale study sound confusing. Basically, the researchers found that fructose affected the brain in ways more likely to lead to overeating and weight gain. This was substantiated with images of how the brain areas were affected, depending on the sweetener that was consumed.
The scientists point out that “increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance.”
In other words, diets high in fruit and fruit juice and beverages and foods sweetened with fructose can lead to weight gain and insulin resistance because fructose does not leave us feeling satiated, whereas sucrose apparently does.
This study provides great insight into what we should consume and how it can change out body chemistry. I look forward to more studies in the wake of this one.