Fructose, also known as fruit sugar, is a popular sweetener used in snacks and soft drinks.
Americans love their soda, and if you’re typical you’re drinking about a gallon a week. Note: that’s about 18 oz per day, or a can and a half.
And don’t rely on labels to tell you how much sugar there is in your soda. The Childhood Obesity Research Center reports that there is a frightening disparity between what labels say about fructose content, and what’s really in there. In fact, there’s about 18% more fructose in the high fructose corn syrup (HFCS) than what you see on labels (1).
But let’s get our terms straight.
Fructose, glucose, and sucrose are types of simple sugars, which are found naturally in whole foods. In fact, many people think fructose is A-OK to consume because it’s what is found in fruit. Consuming the fructose in fruit is generally acceptable because you’re also getting fiber, vitamins, and minerals like iron and calcium. These help the fructose metabolize in your body.
It’s when you extract the fructose and start adding it to things which don’t have fiber and vitamins that you start getting into unhealthy territory. Now your body is coping with too much fructose and no fiber to mitigate things.
You really can’t taste the difference between the three types of simple sugars, but your body considers them to be different things. As a result, your body processes these types of sugars in very different ways. It’s only been a few years since this was discovered, too, which is why there might be a lot of confusion about the varying effects of different types of sugars out there.
1) Fructose. The pathway that fructose takes through your body is completely different from the pathways of glucose and sucrose. The only cells in your body which can deal with fructose are your liver cells. It produces way more fat than glucose, and scientists think it’s actually treated more like a fat than a carb in your body. Inside the liver cells, fructose is also turned into uric acid and free radicals. Not good (uric acid increases inflammation and free radicals cause cancer and disease).
2) Glucose. Your body loves glucose, whose alternative name is “blood sugar”. It uses glucose for energy and secretes insulin in response to higher blood sugar. The body processes the carbs you eat into glucose and uses it for energy. What if you don’t need energy at that moment? It gets stored in muscle cells or in the liver, for later.
3) Sucrose. Slap fructose together with glucose and what do you get? Sucrose. Another name for table sugar, sucrose is also found naturally: in fruit and veggies. The body breaks it down into its two components: fructose and glucose. When you eat sugar, the body takes the glucose and uses it for energy or stores it in the muscles or liver (see above). Unless you’re working out at incredibly intense levels, the fructose goes directly to fat synthesis.
4) High Fructose Corn Syrup (HFCS). I thought I’d throw this one in since it gets talked about a lot in nutrition circles. Like sucrose, HFCS is glucose + fructose, but with slightly more fructose (55%) than glucose (45%). So in that regard, HFCS is really no worse than “real sugar”, or sucrose. There’s even a study to back that up (2).
Now, for some “good” news about fructose.
Fructose supporters claim that since it’s natural, it’s a good product, They also cite the fact that fructose is much sweeter than table sugar, so less is needed to make things sweet (3). That results in less overall calories delivering the same level of sweetness.
They even claim the national obesity epidemic is not due to fructose, since obesity is the result of many things, not just one. They point to several studies which seem to support this idea (4). We’re consuming way too much fructose. Much more than what’s needed simply to make things sweet: we like things SUPER sweet and we like to consume them in large quantities often.
If you’re overweight, you should avoid fructose. Your body can process all three types of sugars just fine. It’s just that when you overload your system that things get out of whack.
The takeaway: fructose turns into fat. Glucose doesn’t.
And it’s not only your liver that’s affected. Researchers are now looking into what high doses of fructose does to your brain.
A Yale study (5) watched what happened when 20 adults of average size were given drinks with lots of glucose or fructose. They were subjected to MRIs before and after the drinks.
For the participants who drank the sucrose drinks, there was reduced hunger activity in the brain. Their brains also signaled “satiety”, or feeling full. For the fructose drink recipients, this brain activity did not occur.
The takeaway: Fructose affects the brain differently than sucrose and may cause us to overeat.
No kidding, your liver turns fructose into fat. When liver cells break down the fructose (remember from above: they’re the only kind of cells which can handle fructose), they turn it into fats which get added to your fat cells.
When you consume too much fructose, it becomes a toxin to the liver. It leads to insulin resistance and what’s called “fatty liver disease”.
The takeaway: Fructose is like alcohol to your liver: highly toxic if you consume too much.
Fructose should be largely avoided by most people, especially if you’re overweight. Since your body treats excess fructose like a fat, metabolizing it in the liver and creating fat, bad things happen. Getting fatter is only part of the story. For an in-depth analysis of how bad having a fatty liver really is, the Harvard School of Public Health published a great summary (6).