Why Those With Thyroid Conditions Should Minimize Fructose Consumption
Published December 14 2015
Over the last few decades the consumption of fructose has greatly increased. Although eating small amounts of natural foods with fructose (i.e. fruit) isn’t a problem for most people, many people consume too much fructose. While fructose has a low glycemic index, consuming high amounts can potentially lead to conditions such as insulin resistance, obesity, hypertension, type 2 diabetes, and even Alzheimer’s disease. And while many people reading this are aware of the negative impact of high fructose corn syrup, eating too much fructose from natural foods can also be problematic.
So you can have a better understanding as to why you want to minimize your consumption of fructose, I’d like to briefly talk about the chemical properties of glucose. Fructose actually has the same chemical formula as glucose, although its metabolism differs greatly from that of glucose (1). Whereas glucose mostly escapes first-pass removal from the liver, fructose does not (2). So unlike glucose, fructose is mainly removed by the liver after intestinal absorption into the bloodstream, and in the liver it is used to produce glucose, fatty acids, or lactate (2).
Why is this considered to be a bad thing? Well, the problem is that fructose is processed by the liver and is frequently converted into triglycerides. While this isn’t a big deal if someone eats small amounts of whole foods which contain fructose such as fruit or honey, if someone is eating a lot of foods high in fructose, especially high fructose corn syrup, then this can cause an excessive amount of triglycerides being produced. In addition to leading to high triglyceride levels, it also alters hepatic glucose homeostasis. In other words, the liver plays an important role in glucose metabolism. The liver helps to control the production of glucose, but eating high amounts of fructose disrupts this glucose metabolism.
Fructose and the Maillard Reaction
Fructose, glucose, and lactose are reducing sugars, and they react with proteins to form a substituted amino sugar in a process called glycation, which is an inflammatory process. Glycation involves the binding of a protein or fat molecule with a sugar. This is also known as the Maillard Reaction, and the glycation of proteins by glucose is considered to be the first step in this reaction (3). The reason why this is important is because this reaction leads to the formation of advanced glycation endproducts (AGEs), and these in turn cause oxidative stress and play a role in the aging process. Research shows that these AGEs influence physiological aging and can also increase the risk of developing conditions such as diabetic nephropathy, Alzheimer’s disease, and even amyotrophic lateral sclerosis (4) (5) (6). So yet another consequence of consuming high amounts of fructose can be a greater formation of AGEs.
What Does The Research Show Regarding Fructose?
There is plenty of evidence showing that consuming high amounts of fructose on a regular basis can cause an increase in hypertension, obesity, type 2 diabetes, kidney disease, and cardiovascular disease (7) (8) (9). One of the biological mechanisms involves the synthesis of uric acid, which is linked to fructose metabolism (10) (11). And so consuming large amounts of fructose can in turn cause an increase of uric acid, which in turn can contribute to conditions such as cardiovascular disease and kidney disease. Keep in mind that most of the research on the harmful effects of fructose have been performed on rats. And so more human studies definitely are needed, but it probably is still a good idea to minimize your consumption of fructose. For anyone interested in learning more about the harmful effects of fructose I would highly recommend checking out a journal article entitled “Adverse Effects Of Dietary Fructose“, which was written by Dr. Alan Gaby.
But How About The Low Glycemic Index of Fructose?
Whereas glucose has a glycemic index of 100%, fructose has a glycemic index of approximately 23% (2). Because it has a low glycemic index, fructose doesn’t raise blood glucose or insulin levels like glucose does, and so it has been recommended for people with type 2 diabetes. However, even though it doesn’t directly affect the blood sugar and insulin levels like glucose does, for the reasons I described in this article, consuming large amounts of fructose can have a negative effect on your health. Plus, it should be noted that while fructose has a low glycemic index, high fructose corn syrup has a glycemic index of 73% (2).
Dr. Joseph Mercola has written numerous articles on the harmful effects of fructose. He recommends to keep your total fructose consumption below 25 grams per day in order to minimize glycation. And if you have elevated uric acid levels he recommends to limit your consumption to 15 grams or less of fructose per day.
Since fruits contain fructose, you might wonder if you should also minimize your consumption of fruit. I think it depends on the person, as some people with certain conditions such as insulin resistance, candida overgrowth or SIBO might need to minimize their consumption of fruits. On the other hand, other people can eat three or four servings of fruit per day without a problem. After all, fruit has some healthy phytonutrients, and it is a good source of fiber. Similarly, most people do okay eating a small amount of sugar. Although it is possible to overdo it with foods such as fruit and honey, of course the main concern with fructose has to do with refined foods, and especially beverages which are sweetened by adding fructose.
In summary, while eating small amounts of fructose is fine in most people, many people eat large amounts of fructose on a frequent basis. Although fructose has a low glycemic index, it is processed by the liver and is converted into triglycerides, and it also disrupts glucose metabolism. This can increase the incidence of obesity, insulin resistance, non-alcoholic fatty liver, and type 2 diabetes. In addition, eating large amounts of fructose can lead to the formation of advanced glycation endproducts (AGEs), which can increase the risk of developing other chronic health conditions such as diabetic nephropathy and Alzheimer’s disease.