There seems to be great debate over whether fruits should make up part of our diets, and if so how much due to the presence of fructose in them. Let’s review some basics and some more information you may not have known about fructose, so that you can make a wise decision.
What is Fructose?
Fructose (also called fruit sugar or levulose) is a type of sugar; specifically, it is a simple carbohydrate. The simplest forms of sugars are called monosaccharides. Fructose and glucose are both monosaccharides. This just means it cannot be broken down any further. Most sugars are disaccharides, which are combinations of monosaccharides. An example would be sucrose which is common table sugar. It is one part fructose and one part glucose.
It is important to note that fructose is the sweetest of all sugars. Glucose is about half as sweet in comparison. This is important because it would seem we are hard-wired to seek out sugary foods. I have seen studies where babies would stop crying when fed sugar water, but not regular water, and many other interesting studies.
How does fructose metabolize?
For most carbs, they get handled very easily by our body. They either get used as energy (from converting to glucose) or they are stored as fat. Fructose gets sent to the liver to be metabolized, though, so it is unique. There is an enzyme called fructokinase that is primarily in your liver, intestines, and kidneys that very quickly metabolizes it. It happens so fast, a few bad things happen. The fructokinase enzymes break down the fructose rapidly, so quickly in fact that the cells burn up their ATP. All the scientists say fructose is an “expensive” food because this process drains your cells energy bank accounts. So why is this bad? Good question. It is bad because your cells go into a state of shock. Studies show the cells act like they are ischemic (have no blood supply). They know this because of the stoppage of various cellular functions. This leads to oxidative stress, increased uric acid, and other bad things. If you are wondering what kind of cells I am talking about, it can be fat cells, liver cells, or even cells that line our blood vessels. The cells that are most susceptible to this are fat cells. The human body is amazing, though, and these cells do have a self-protect mode they go into. They start filling up with fat, lots of fat (yes you will get fatter as a result), and some glycogen as some protection for the next fructose attack.
Another good fact to know, glucose accelerates fructose uptake. Most fructose you consume is mixed with glucose just due to the way food is sweetened and occurs in nature. Furthermore, the transporters that take up fructose, over time get better at actually transporting it. What does this mean in plain English? The transporters allow for more to be absorbed. The longer you eat fructose, the more magnified the metabolic effects will be.
How does fructose affect insulin levels?
Because it is metabolized by the liver, fructose does not cause the pancreas to release insulin the way it normally does in response to carb consumption. Writing this made me think about all the candy the doctors used to tell us to get my great grandma who was a diabetic. We were instructed to get candy sweetened with fructose, or sorbitol (which breaks down into fructose). So anyway, there is no surge in insulin. In case you are wondering, the Glycemic Index rating for fructose is 20. Here is the main problem I see with fructose. There is a mountain of evidence that demonstrates a high correlation of developing insulin resistance setting up a higher probability of having type 2 diabetes down the road when you consume excessive levels of fructose. I have seen firsthand the effects of diabetes on long gone family members who lost sight, experienced nerve pain/damage, and other issues.
Most of you probably know what this means, but for others of you who are learning, your cells typically take in glucose and other things via insulin. It is a key to a door. Well, fructose can cause the key not to work well. So now instead of glucose being stored or used, it stays in the blood. This is not good. This creates a condition called hyperinsulinemia (too much insulin in the blood). One of your body’s primary responses to excess insulin in the blood is fat storage, but we will get to this later. This is just the beginning, however. Your liver begins to get insulin resistant. When the liver becomes insulin resistant, its production of glucose becomes deregulated. The liver can no longer turn off its glucose output in response to when you eat carbs. Think about this. The person with insulin resistance may not be eating carbs, but his liver might still be making carbs (that is, glucose) all the time. To control the resultant high blood sugar, the pancreas must produce even more insulin. That might get the blood sugar down in the short term, but in the long term, it will make the liver, even more, insulin resistant. Eventually, still more unwanted glucose will be produced by the liver, and even more, insulin will need to be released by the pancreas. Ugly isn’t it?
In this process, we now start to hammer the pancreas. It now starts to suffer insulin resistance. It releases insulin erratically. Sometimes it allows the blood sugar to go too high. At other times the pancreas overshoots the required amount of insulin, and the blood sugar drops too low. This leads to the phenomenon called reactive hypoglycemia.
What other bad things can fructose do?
Serum triglycerides rise – Fructose raises serum triglycerides significantly, as it causes liver cells to produce triglycerides. Elevated triglyceride levels in the blood can be a leading sign that someone can be headed down the path to heart disease. This is why it is so important to keep your triglycerides under 150 mg/dl.
Obesity – Fructose can lead to obesity. I found an interesting story about an indigenous tribe called the Maori in New Zealand. In old times, they lived on fish, sweet potatoes, and veggies. They were lean, muscular, and extremely healthy. In the 19th century, the European settlers started arriving. They brought sugar and lots of it. Now about 1 in 4 have diabetes. It used to be non-existent. This is just one story, but I think it is great to review and learn lessons from mistakes made throughout time. Dr. Weston A Price was a pioneer in this regard, and his incredible journeys around the world and similar stories can be read in his book Nutrition and Physical Degeneration.
So let’s get back to the topic – obesity. This ties to the above statement about serum triglycerides. When you eat more than you burn off, your liver will convert the excess into triglycerides, which will then be stored in fat cells for later use. It is important to understand this as fructose causes your liver to produce large amounts of triglycerides by itself! More triglycerides equal more fat. The result is a phenomenon called fructose-induced lipogenesis.
High blood pressure – Fructose-induced hypertension is often right behind insulin resistance. There is a mountain of evidence supporting this as well.
Leptin and Ghrelin connection – Most of you have probably heard about leptin. It is an actual hormone that is released from fat cells. It tells your brain that you are satiated when you eat. Ghrelin, on the other hand, does just the opposite; it promotes actual hunger. When you eat fructose, it does not affect leptin or ghrelin. You can eat lots of garbage fructose laden calories, and still not feel full via the leptin signal.
The Benefits of fructose
So is all fructose bad? No way. Remember up above when I talked about how sweet it is, well think about some yummy fruits like oranges. Would you want to eat them with no sweetness to balance the sour taste? Moreover, we do know that fresh fruit and veggies (yes some veggies have fructose too), are good for you as they provide various vitamins, minerals, antioxidants, fiber, polyphenols, etc. I say anything that makes food that is good for you taste better is a good thing.
As someone who trains hard, here is another benefit. Fructose increases the speed at which you can absorb and burn glucose. When you are training, being able to conjure up energy is an excellent thing! This might be why people who do things like hiking take dried fruits. Now let me make one thing clear here, I am not talking about PURE fructose, as I mentioned above, it burns up ATP too rapidly. The foods people eat are a package with other sugars and carbs to go along with the fructose.
How much fructose is acceptable?
Typically around 15-25 grams a day is a good amount to consume.