About sugars and (dis-)metabolism


So, if you have been trough my previous post “About sugars and addiction“, you might now be wandering why that matters… And what it means that glucose and fructose behave differently in our body… And why that matters too… Brace yourself and enjoy the ride on the next part of the post, where I hope you will find your answers (and hopefully raise more questions for my next posts)…!

Once foods enter the body (any food), they get broken down (mechanically by the teeth, chemically by enzymes and digestive juices secreted by the salivary glands, stomach, pancreas and liver and again mechanically by the stomach and intestine movements) into their smallest constituents. Guess what? All digestible carbohydrates (not the pre-biotics for example, which as you know by now, are non-digestible carbohydrates) will eventually end up in glucose, fructose or galactose. After being broken down to their smallest parts, the mono-saccharides get absorbed. Absorption requires a passage through the liver where the first major difference between glucose and fructose becomes evident (and this matters to your health!).

While glucose can in fact be metabolised both in the liver and in other tissues and is rapidly released into the bloodstream (causing release from the pancreas of the hormone insulin of which I will detail soon), fructose is almost completely metabolized in the liver. Here it goes broadly into three pathways: 1. It is used for energy by the liver (more efficiently than glucose); 2. It is converted glucose (and released into the bloodstream) or glycogen (and used as storage); 3. It is converted into fats through a process called “de novo lipogenesis” (formation of lipids from scratch…) and released as either tryglicerides (TG) or low-density lipoproteins (LDL) or kept in the liver for storage.

The diagram below shows schematically the fate of fructose once into the liver… As you will see, the numbers show the average amount that take each of the described pathway. Numbers can only be a simplistic estimation, as they depend on a number of factors, including: the person age and gender, the liver health, the amount of other nutrients absorbed in the meal, the body state (rest, activity, recovery, etc…), the general body health (insulin sensitivity, etc…), etc…


The fate of fructose in the liver
The fate of fructose in the liver


At this point I believe it is essential to reinforce one aspect of modern diets: if it was estimated that in the early part of the 20th century (forget all the paleolithic stories, no need to go that far…) we were ingesting fructose mainly from natural unrefined sources (whole fruits and vegetables) and in big part in the form of sucrose (50% fructose and 50% glucose), nowadays most fructose is ingested in its simplest form as high fructose corn syrup (in the case of the more and more average diet, consisting of little produce and much ready made meals, sweets and soft drinks…). The reason why this is relevant is that the amount of fructose the liver has to deal with has significantly increased, together with an increased speed of delivery from the intestine to the liver (due to the absence of other nutrients that slow down the absorption, thus giving time to the digestive system to deal with the workload) and a reduction in all other nutrients that in nature are associated with it (fibers, vitamins, minerals, proteins, etc…). This has been extensively proposed as one reason for the “toxicity” of fructose. High amounts of fructose in the liver (and potentially the innate or acquired inability of the liver to deal with it effectively) have in fact been linked not only to increased blood cholesterol and triglycerides (simply speaking, some fats that increase the risk of cardiovascular disease), but also to a liver condition similar to that caused by alcohol (and for that reason called non-alcoholic fat liver disease, or NAFLD). In the link page, under the “About sugars and metabolism” heading, you will find a number of scientific papers published in peer-reviewed (i.e. good quality) journals, talking about this…

The key points to understand about fructose until now then, are: 1. Fructose is only metabolized in the liver, as opposed to glucose that can be metabolized in almost every cell in the body; 2. When high doses of fructose hit the liver at a high rate (as when drinking HFCS-sweetened beverages for example), the liver capacity to deal with it can be challenged and taken past its limits. When this happens, fructose is turned into fats, potentially increasing the risk of cardiovascular disease and non-alcoholic fat liver disease. In addition, the presence of fructose will inhibit the use of already present fats (both because you are already getting energy from fructose, and because fructose can be turned into fats if needed) and if also high doses of glucose are ingested concurrently, they will end up in storage (because fructose is used at a faster rate).

And what about glucose then? Is fructose the only villain? Unfortunately not… As mentioned earlier, when glucose enters the bloodstream, the hormone insulin is released by the pancreas to help maintaining blood sugar levels within a tight range. Blood glucose is in fact a highly controlled parameter (by itself something that should make you think that nature does not want uncontrolled boood sugar levels…). If it is true that glucose is essential for the cell metabolism, high circulating amounts can have deleterious effects on the cardiovascular system (arteries walls in particular) too. When insulin is released, it allows glucose to exit the blood stream and be absorbed by the cells, where it can be used to produce energy (or be stored as glycogen). Not only by doing this insulin controls the amount of circulating glucose (essentially reducing blood glucose), but insulin also sends a satiety message to the brain, informing your body that it has now enough available energy and does not need to eat anymore. Because insulin is cosidered the hormone of energy storage (as it is mainly released in the presence of glucose and proteins in the meal), nature also made it the hormone that prevents the burning of fats as energy sources (why should you use fat if you need to reduce the amount of glucose in the blood already?). Up to this point, everything would be as nature intended… You eat a balanced meal, your body breaks down the food into its most basic constituents and absorbs them while telling your brain that it has had enough.


Metabolic fate of glucose
Metabolic fate of glucose


However, as with fructose, problems arise when the amount of glucose to be dealt with becomes too high (as it is the case with overconsumption of sugars). Constantly high amounts of glucose in the blood cause a constant release of high amounts of insulin by the pancreas. In a similar way to how you stop hearing the train passing by if you live near the railway, the cells stop responding to insulin presence when it is constantly high… This is what doctors would call insulin-resistance. Because your body needs to lower blood sugar levels somehow and does not know other ways, it causes the pancreas to release more insulin (like a baby crying louder when the exhausted parents ignore the early screams…). At this point a blood test would likely show increased blood insulin levels and you would be diagnosed with hyper-insulinaemia. At this stage you are already facing a serious issue, because food that in normal conditions would cause a minor release of insulin, now has a much amplified insulin-response. That means less fat-burning, less feeling of satiety and more fatigue (so even when you start limiting sugars intake, that might not be enough to lose fat as you were hoping…). In addition, as the word gets nastier and less pronounceable, you get closer and closer to the point of no return… Even more problems arise when despite the increased release of insulin (hyper-insulinaemia), your blood sugar levels remain high, a situation called hyper-glycaemia (even the loudest cries of the baby have no more effect on the parents, your cells). At this point the doctor will probably label you as diabetic (after confirming other signs like the increase in blood sugars after a meal or their fasting levels)… Not only your insulin levels will be constantly elevated, your blood sugar out of control and your fat stores only increasing; your body will now be under a metabolic attack and molecules related to inflammation will start spreading into your system… It seems this low-level inflammation (measured via the presence of high-sensitive C-Reaction Protein – hsCRP – in your blood) is ultimately what causes (or at least is involved with…) the number of medical conditions that are often (scientifically or anecdotally) associated with diabetes or (see next…) the Metabolic Syndrome.

If up until here increasing activity (exercising more…!) and modifying your diet (reducing sugar intake) have scientifically proven chances of bringing you back to the right path (your cells can still get back to “hearing” the presence of insulin, therefore reducing the release of it from the pancreas while still lowering your blood sugar levels to a safe range), if left ignored, the constant hyper-activity of the pancreas to produce more and more insulin will end up causing the cells in the pancreas to burn out… This is a sort of a tipping point… Your pancreas would now be unable to produce insulin, so that the only way for you to stay alive would be to inject yourself with insulin any time you have food… You would be now labelled as insulin-dependent diabetic, and your life would be changed forever…

Can it get worse? Sure it can…! If you remember the part on fructose and its role in increasing circulating fats (LDL cholesterol and triglycerides) and you consider the post on sugar addiction, good chances are that once you get to the stage of diabetes (and even worse when insulin-dependent), you are overdoing on anything sweet… And unfortunately for you, once you past the early stage (your body starts to become less sensitive to insulin – you have been labelled insulin-resistant) you do not even really need to be gorging on sweets, because even little amounts of sugars now will cause a storm-like reaction…! It might even be the case (because you are addicted, it is convenient, it is present everywhere and maybe you think it is not that bad either…) that you are also overindulging in processed foods, sweets, soft drinks and all the rest (pasta, rice, pizza, bread, crackers and most bakery products should also be on your black list by now)… That means you are probably overloading your system with both fructose (that increases circulating fats, makes you overeat by not releasing insulin and loads you with calories) and glucose (that keeps your insulin levels too high for you to burn fats and adds more calories).

You are now likely to be overweight to say the least… And guess what? High LDL cholesterol, high triglycerides and high blood sugars are already three major risk factors for cardiovascular disease… Add a large waist line (you have been adding more and more calories while burning less and less fats…) and high blood pressure (the reasons for this are less known, but likely to be at least in part related to the hardening of blood vessels caused by elevated circulating sugars and the low-grade inflammation discussed above) and you are in full-on Metabolic Syndrome… If you also recall the systemic inflammation burning you from the inside (the high-sensitve C-Reaction Protein test), you are now in the front line to suffer from cardiovascular disease… Does that not scare you? Think heart attack and stroke, that might work better…


Dis-metabolism of excessive sugar intake
Dis-metabolism of excessive sugar intake


Because the scope of my blog is not just to scare people, what I really wanted to highlight with this post (and the previous ones) is that we are ultimately in control of our body. We are the only responsible for our health and with the exception of a minority of cases, genes play only a partial role, our behaviour (the so called epi-genetic) ultimately is what brings us down the healthy or ill path.

And the reason why I felt (and I hope) that my knowledge and experience could help you is that as I read in a textbook on basic human nutrition, we live in a “toxic, obesogenic society”. I am not joking, nor exaggerating. And that is why I do not even blame people for being overweight, diabetic, having the Metabolic Syndrome or all the rest… Going to the supermarket nowadays is truly like entering a drug store. We are so surrounded by unhealthy foods (and drinks), even marketed as “healthy”, packaged in beautiful green boxes, etc… that we end up believing what they tell us… Beware of the words “organic”, “natural”, “low-fat”, just to mention some… They mean nothing in terms of health…! An organic product (certified organic) only means that its making process has followed some specific standards… A jar of jam with 60% sugars can be organic, is that healthy? Or a chocolate bar in which no more than 40% is cocoa (it leaves most of the remaining 60% to sugar…) can be organic… Even worse for “natural”… A stone is natural… Would you have that? What is not natural actually? And low-fat was the big thing during the years of the nutritional war on fats… These years are quickly becoming a thing of the past (now that we know that some fats are not just good, but even essential and that we have seen that eating “low-fat” foods made people fat…), but unfortunately the low-fat claims resist and very often hide the “high-sugar” label…

But, eventually, what is the ultimate goal of the food industry? To take care of your health or to sell you more of their stuff? Have a thought, I do not think I need to help you find the answer… What I would like to help you doing, is to make sure you know how to avoid falling into the “Big Food” trap, how to make healthy choices and to realize that you can still enjoy great food and experience delicious tastes and flavors (even more that you do now!) while maintaining a good health…

For this, my next post will be on practical tips and how to put the theory into practice (how do you reduce sugar intake?). I have come to realise that even if the theory is there, it is often not easy to know what to actually choose while at the supermarket, or in the kitchen… How much sugar is there in bread? And what is the proportion of sugars, fibers, fats and proteins? Are white bread, sourdough bread, brown bread or multi-grain bread all the same? And what about pasta? And fruits? Are all desserts equally bad? Do you think you are doing yourself good by eating cereals in the morning? Have you seen that most of them are packed with sugar? And did you know that one tablespoon of ketchup contains at least one teaspoon of sugar? This and more is what you will hopefully come to know soon, so stay tuned…!