Agave in the Wild – Sweet. Really Sweet. Photo by Juan Gnecco, FreeDigitalPhotos.net
Fructose Effect On Brain May Explain Link To Obesity
Sources: Medical News Today & Journal of the American Medical Association (JAMA)
Do you shun high-fructose corn syrup as a processed chemical but love agave as a natural sweetener? Believe it or not, you might actually be better off with the high-fructose corn syrup (ideally, you’d reduce how much you have of both). A recent study by Page et al. in JAMA found that consuming fructose (compared to glucose) led to lower blood flow and activity in the part of the brain that regulates appetite and lower levels of the hormones that lead to feeling full. And most agave nectars have significantly more fructose than high-fructose corn syrup.
First, a somewhat brief lesson on carbs, how fructose plays a role, and why you should care.
Like glucose, fructose is a mono-saccharide – an individual building block of larger carbohydrates. For those counting, the third mono-saccharide is galactose. Think of these guys as the individual Lego-blocks.
Most of the carbs we know, or care, about (dairy, pasta, bread, sugar, etc.) are built from these Lego-blocks. There are two frequently used terms here: simple sugars/carbs and complex carbs. Simple sugars refer to mono- and di-saccharides. Disaccharides are made up of two (di-) Lego pieces put together. The three di-saccharides are:
Mannose – Two glucoses – Rarely found in food alone, usually a part of larger chains called polysaccharides (aka complex carbs)
Lactose – One glucose and one galactose – Typically found in dairy foods
Sucrose – One glucose and one fructose – Typically found in naturally occurring sweet foods (fruits) and processed foods.
Long-story short, larger carbohydrate Lego structures are considered complex carbohydrates. These are typically the carbs found in pasta, rice, bread, veggies, legumes, etc.
Technically, it’s easier to break down simple carbs in the body than complex ones just as it’s easier to break apart a smaller Lego structure than a bigger one. But not so fast; most carbs are not delivered by themselves in a nice, neat package (you don’t eat a spoonful of mannose or lactose) – they are grouped together with other nutrients like protein, fat, fiber and water. The key is what package the carbs are delivered in – so not every simple sugar is bad for you (fruit vs. candy) and not every complex carb is a healthy option (refined pasta vs. quinoa).
Now you know carbohydrates. Moving on to our featured carb, fructose…
Fructose, because it’s absorbed differently by the body (via the liver) than glucose, has a lower glycemic index (GI) rating – the rating system used to measure how fast a single food increases your blood sugar. That’s why things like agave became all the rage when any and all low-GI foods were “the thing.” And there’s still some potential value for athletes and diabetics (to be discussed in future posts).
However, just because it’s absorbed slowly doesn’t mean it should be absorbed to begin with. Most of us don’t go around eating 100 grams of isolated carbs (well, except for Pixy Stix, Fun Dip and other sugary snacks). If you’re eating carbs with other foods like protein, fiber or fat, the whole GI rating system goes out the window. The take home message from all of the low-GI gurus became: eat more fruits, veggies, whole grains, healthy fat and lean protein. Eat less junk food. Big surprise.
As expertly pointed out by Medical News Today, our two main sources of fructose these days is fruit and processed foods. Fruit packages the fructose with lots of water (most fruits are more than 90% water by weight) and fiber. The fructose is also likely trapped within the tough-to-digest cell walls of the fruit, which means digesting the fructose is harder (unless you juice it). Imagine surrounding the Lego-blocks with a taped-up cardboard box. You have to open up the box before you get access to the fuel (more effort required for breakdown) and if the boxes are moving on a conveyer belt similar to your digestive system, you may not get to all of the boxes, so some goes undigested (which means less calories).
In many processed foods, fructose is added to make them sweeter and more shelf stable. These foods, on the other hand, don’t always have water, fiber, or nice natural walls to make accessing fructose harder. It’s a party train of absorption all the way down the digestive tract! But we shouldn’t just pick on little old fructose, because he’s rarely found in isolation; he’s usually teamed up with glucose as a part of sugar (50% fructose / 50% glucose) or high-fructose corn syrup (55% fructose).
Per the study above, fructose fails to regulate the reward and appetite system in our brain so we tend to overeat when eating large amounts of fructose compared to glucose. But my frustration with this study is: the average person doesn’t drink a “glucose” or “fructose” solution. They drink juice, eat fruit, eat brown vs. white rice, drink soda and eat candy bars. Which is a combination of nutrients and physical properties that lead to different absorption rates.
My take home from this study? Eat less processed junk. And run a study comparing MRI images of the brain on apples vs. soda vs. meal replacement bars with man-added fiber. Also, consider how many apples you’d need to eat to get the same amount of fructose as a candy bar or soda.