I have always had a sweet tooth. A package of bakery cookies from the grocery store lasted about 24 hours in my house growing up and if you weren’t quick, you missed out. And to be honest, I still struggle with a sugar addiction, though I’ve developed healthy habits for dealing with it. Generally, I will try to eat very limited/no added sugar during the week and then eat whatever I wish on the weekend. By reducing my sugar intake during the week, it makes my tolerance for it on the weekend much lower and so I consume less. However, Adam and I will still eat a sleeve of oreos before making it home from the grocery store on occasion. I feel that if your diet is tight during the week (very limited added sugar, sweetened beverages like juice or pop and limited/no refined foods such as bread, pitas, wraps, granola bars, baked goods, etc.) and you are active daily, then you can pretty much enjoy whatever you like on the weekend (after a while of eating like this you likely won’t want much junk on the weekend anyway, just a taste). You must be honest with yourself though and if it becomes too difficult for you to transition back on Monday, then this isn’t the best strategy for you. Everyone is different and I will mention some tips for reducing your sugar intake at the end of the post.
I’d like to go over some basics when it comes to sugar because there are so many misconceptions. First of all, sugar is a carbohydrate and there is sugar in fruits and vegetables, which are also carbohydrates (some contain small amounts of protein, however, they are primarily carbohydrate). The difference between fruits, vegetables or other plants we eat and anything with added sugar is the sugars in fruit and vegetables are bound in a fibre matrix. This is important because it takes more energy for the body to cleave these sugar molecules from fibre molecules and the absorption process happens more slowly, creating less of an insulin spike in the blood. When you consume fruit juice, pop, candy, ice cream, baked goods, anything with added sugar, the sugar molecules are free or unbound and are readily absorbed by the intestines creating an insulin spike.
Our blood sugar is very tightly regulated at around 5 mM, which is a measurement of concentration. The brain prefers almost exclusively glucose as a fuel source (unless you eat an extremely low amount of carbs or you have been without food for several days, in which case the brain will use ketones; a product of fat breakdown- another topic for another day). When you eat a meal, the concentration of sugar in the blood will rise above 5 mM stimulating the release of insulin from pancreatic ß-cells. The primary job of insulin is to facilitate the movement of glucose from the blood to your cells as they use it for energy. Insulin stimulates glucose receptors to move to the outside of the cell enabling glucose to attach to the receptors and become internalized. When the cell has sufficient glucose, it will move its glucose receptors back inside the cell preventing further glucose absorption. Without sufficient insulin, blood sugar climbs too high, creating many detrimental effects, which is why it is so important for diabetics to receive insulin.
Insulin affects the body in other ways and can modulate food intake (1). Hormones are one way our body sends messages. Nerve impulses send messages quickly and typically have a short effect. Hormones act slower, however, their effects last much longer. There are several hormones involved in the regulation of food intake, one of which is leptin. Leptin is a satiation hormone, inhibiting food intake. When insulin is released, it increases the release of leptin (1), inhibiting further intake of food which makes sense because you’ve just eaten, raised your blood sugar, stimulated insulin, which increased leptin, telling the body to stop eating creating a negative feedback loop.
Glucose and carbohydrates in general, are used primarily in the body for energy. Fat and protein can be used as energy as well, however, they have many other purposes in the body. Every carbohydrate we eat, aside from fibre, whether it is sugar, rice, bread, fruit, candy, etc., gets converted into glucose, with a few minor exceptions. Carbohydrates are broken down by enzymes in the intestine and are typically absorbed as glucose and then sent, via the portal vein, to the liver. Our liver is one tissue helping to regulate blood sugar; if our blood sugar dips, the liver will release glucose into the blood to correct for low blood sugar. If our blood sugar is at an adequate concentration, the liver will store glucose as glycogen. The liver can hold several hundred calories worth of glycogen to maintain blood sugar. When these reserves are full, the body will begin to convert the extra glucose to fat to be stored. We also have glycogen reserves in our muscle so energy is readily available for when we move. When we exercise or simply move about, we deplete these reserves. We also use fat for energy and release free fatty acids and glycerol into the blood, which get absorbed into our cells and used for energy. We use a certain ratio of fat and glucose for energy, depending on the nature of activity. Our liver tries to conserve some glycogen in order to tightly regulate blood sugar for the brain, which is why we also use fat when we are active and at rest. If we didn’t, we would run out of glycogen within minutes of intense exercise and we would faint due to lack of glucose to the brain.
*There are ebbs and flows all over the body as it tries to maintain homeostasis. So, it is important to remember your body is never strictly breaking down glucose molecules for energy (catabolism) and never strictly building up glycogen or triglycerides (fat) for storage (anabolism). There is always a net ratio of this activity going on, which happens for almost anything going on in the body.
If one is regularly inactive, like many North Americans are, glycogen reserves remain topped up and any additional food eaten typically gets stored as fat. In this situation, it is advantageous to go several hours, at least 4, before eating again. The body appreciates cycles and small amounts of stress of this nature. Additionally, if one is eating frequently and constantly stimulating insulin, the body will compensate and begin to resist insulin, which can lead to Type 2 Diabetes. The development of Type 2 Diabetes has many factors, however, so that is another topic for another day.
Fructose is a monosaccharide (single sugar molecule) and is found in plants. When it is combined with glucose (another monosaccharide) it forms sucrose, or table sugar (a disaccharide). Back in the 60s and 70s, high-fructose corn syrup (HFCS) was developed from, you’ve guessed it, corn, as a cheaper source for adding sugar to food and beverages. Fructose is also sweeter than sucrose (table sugar), creating a sweeter more appealing taste to foods. This has led to many North Americans becoming accustom to hyper-palatable foods, which are foods developed to trigger the reward centre in the brain more so than natural whole foods and flavours. Unfortunately, fruits, vegetables, legumes, nuts and seeds become much less appealing and it becomes difficult to transition from a diet high in refined foods to a diet comprised of mostly whole foods when one’s palate is accustomed to the trinity of hyper-palatability - sugar, salt and fat. However, it absolutely can be done. A week or two without refined foods and whole foods will begin to taste amazing again. Whole foods have much more depth to their flavour and it is unfortunate when they are moved further away from their natural state and covered with extra sugar, salt and fat when creating refined foods.
Fructose has a slightly different chemical structure compared to other sugars and so it’s metabolism is different. As mentioned, insulin stimulates the translocation of glucose receptors to the surface of a cell in order for glucose to get absorbed. Fructose requires a different receptor to enter the cell and this receptor is not insulin dependent (1), meaning fructose does not give an insulin spike. When fructose is absorbed by the intestine, it goes to the liver to be converted to glucose or fat or it circulates in the blood, however, since it does not stimulate insulin, leptin (the satiation hormone) also isn’t released explaining why one feels hungry soon after a meal of refined foods containing HFCS (1). There is a very small population of people who lack the genetic material to produce leptin; these people are typically very obese and the administration of leptin produces a dramatic decrease in food intake in these individuals (1). However, not even close to all overweight individuals would have this genetic predisposition and it would be inappropriate to automatically attribute one’s obesity to genetically caused decrease in leptin. Staying active and eating a healthy diet that is portion controlled would be imperative for these individuals, which doesn’t differ from what I would suggest to anyone trying to lose weight.
As mentioned, fructose requires a different receptor type than glucose for facilitation into cells. Pancreatic ß-cells and the brain lack the receptor that facilitates fructose into a cell, explaining why insulin (remember it’s created in pancreatic ß-cells) isn’t stimulated by fructose and also provides another reason for why fructose isn’t satiating as it’s unable to enter the brain (1). Fructose also has a chemical structure which more efficiently provides carbon atoms for the biochemical formation of fat compared to glucose (1). This results in more fructose circulating in the body leading it to be converted to fat more readily than glucose is.
High-Fructose Corn Syrup is found in almost all foods containing caloric sweeteners, such as soft drinks, fruit juice/drinks, candied fruits, canned fruits, ice cream, flavoured yogurts, most baked goods, granola and protein bars and many cereals and jellies (1). It’s everywhere. Agave nectar (read syrup) has been grouped with natural sweeteners, such as honey and maple syrup as a healthy alternative to sugar, however, it is just as bad as HFCS as it is primarily fructose.
As demonstrated, what happens to food once it enters the body is a very complicated subject. I have provided a simplified version of what happens to sugar in the body. I hope I have provided for you a little more understanding about sugar metabolism because I believe the more you know about the effects of food in the body, the easier it becomes to make rational food choices.
Bray, G. A., Nielsen, S. J. & Popkin, B.M. (2004). Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr, 79(4), 537-43.