Sugar: the main source of fuel for our body

Sugar gets a lot of good and bad attention in today's society. It can be hard to tease through the opinions vs facts in social media, the fitness industry, and health care, or causes vs associations in research about sugar. So what is the truth? In this post I'll break down what sugar really is, its functions in food, and why sugar is important to our health and wellbeing. You will get the truth on sugar. What is sugar, really? Sugar is a molecule made up of carbon, hydrogen, and oxygen. Sugar is another way to say simple carbohydrates: monosaccharides, meaning one sugar molecule, or disaccharides, meaning two sugar molecules, either the same or different strung together. Oligosaccharides, meaning more than two sugar molecules strung together, can also fit within the simple carbohydrates group. Below are some common simple carbohydrates found naturally and added to the foods we eat: Monosaccharides Glucose (like blood glucose or blood sugar) Fructose Galactose Less common forms: Ribose, Xylose, and Arabinose Disaccharides Maltose (2 glucose molecules) Lactose (milk sugar, glucose + galactose) Sucrose (aka table sugar, fructose + glucose) The monosaccharides explained Glucose occurs as a monosaccharide in some foods: honey, sweet corn, grapes, and dried fruits like raisins, apricots, dates, and figs. It's also added to food in processing, in the form of dextrose and corn syrup- extracted from corn or wheat: sauces, condiments, juices, breads or bakery items, and concentrates, to name a few. Glucose is the human body's preferred source of fuel. Whether we consume monosaccharides, disaccharides, or multiple saccharides strung together, glucose will be extracted for use, and other monosaccharides will be converted to glucose and/or glycogen in minimal steps. Unused glucose is stored as glycogen in the muscles and liver- approximately 400-500g in muscles and 100g in the liver. Once these store minimums are met the rest is stored as fat for long term use. Our brain primarily runs on glucose. Approximately 20% of the glucose our body consumes and uses helps brain function. A diet low in carbohydrates could lead to symptoms associated with impaired brain functioning: poor concentration, impaired critical thinking and problem solving abilities, irritability, increased symptoms of anxiety and depression, mood swings and inflexibility, and more. Fructose is the sweetest monosaccharide. It's the main sugar found in fruits, and also occurs on its own in honey, syrups, sugar beets, sugar cane, and some vegetables. It can be produced from corn or broken sucrose bonds in food processing. Fructose and glucose are formed in a 50%:50% ratio to form the disaccharide sucrose, and is produced from sugar cane. High fructose corn syrup (HFCS) is also a ratio of fructose to glucose, just in different percentages such as 55%:45%, and produced from corn. Fructose is mainly metabolized in the liver to then be used for specific functions, such as converted to glucose. Galactose is the third monosaccharide, primarily found naturally in dairy products, plus minimally in avocados, sugar beets, and some gums. Glucose and galactose are bonded by glycosidic bonds to make the milk sugar lactose. In our small intestines, lactose is broken down by the enzyme lactase, releasing the two monosaccharides. Galactose can be converted to glucose to form ATP for cellular energy. It also is part of various macromolecule structures in our body: glycoproteins and glycolipids. The disaccharides explained Sucrose is another word for table sugar, made up of glucose and fructose molecules in a 50%:50% ratio. It's the sweetest tasting of the disaccharides. Sucrose is naturally found in sugar beets or sugar cane, foods we extra our table sugar from. This disaccharide also occurs naturally in fruits and vegetables. Sucrose is added to foods in the form of brown sugar, table sugar, granulated sugar, and syrups. Lactose is the commonly known milk sugar as it's found in mammals' milk: goats, cows, and humans (yes, breast milk). It's made up of the monosaccharides glucose and galactose. Lactose is found naturally but also added to foods such as sauces and meat products. Milk, yogurt, ice cream, and soft cheeses contain a higher concentration of lactose, compared to hard cheeses that have a lower concentration. This difference is due to the increased aging process of hard cheeses and greater extraction of the milk protein whey (composed of proteins, fats, and lactose). Maltose is composed of two glucose molecules. This disaccharide is found naturally in barley and wheat, not typically in its raw form but formed during the malting (browning) process. Molasses is a concentrated maltose, a stand alone food item or added as an ingredient to energy/cereal bars, baked goods, breads, and cereals. Functions of sugar in the foods we eat Sugar has different functions when added to food: nutrients, sweetness, palatability and texture, and can improve shelf life. Added sugar (in terms of the monosaccharides and combined saccharides, zero calorie sweeteners are a whole other topic) meets all these functions. Naturally occurring sugar will give you whatever texture, flavor, and nutrients of the food it's in. Why our bodies need sugar As mentioned above, glucose is the main source of fuel for our bodies. The body can convert protein and/or fat into glucose: proteins can break down to enter our body's cells for energy conversion, or ketones, a fat molecule's byproduct, can also be a usable form of fuel. However, glucose is the preferred source, the innate method to eventually form a usable cellular energy product. I'm going to explain why and how this is by making you think back to high school biology. Remember a little thing called the Kreb cycle? Glucose is converted in a final step here to regulate various systems in our body. The human cells are permeable to glucose, and once in our cells it first breaks down into pyruvate, then 2 acetyl CoA molecules. Each acetyl CoA contributes to 1 round of the Krebs cycle. The most important product of this cycle is adenotriphosphate (ATP), a usable form of cellular energy. Without this energy source we would struggle to function as a whole. Inadequate carbohydrate consumption could lead to obviously low cellular energy. On the surface it presents as some of the following: head/brain region impaired cognition irritability worsened anxiety, depression, or mood disorder behaviors headaches dizziness and/or lightheadedness impaired vision respiratory, circulatory slowed heart rate weakened heart muscle poor blood circulation (leading to dizzy/lightheaded/faintness) heart palpitations muscles and bones atrophy, weakness brittle bones, like early onset osteoporosis joint pain and muscle aches easily fractured bones fatigue may impact your ability to perform a similar exercise routine or activities of daily living metabolism and digestion slowed metabolism- reversed with improved, adequate carbohydrate intake nausea constipation/diarrhea the body starts breaking down ketones instead (fat's byproduct) less satisfied after eating (also complex carbs) weight fluctuations (up or down) …and more Carbohydrates are a food group regularly demonized in mass media, and we are told to avoid it at all cost. As I've just explained in the above sections, sugar plays a key role in the food we eat AND is our bodies' main source of fuel. Our body thrives on sugar. In later posts I will review the latest research on sugar and debunk common nutrition myths about this nutrient. If you want to learn more about the simple carbohydrates, such as their function and how much to regularly consume, start by reaching out to one of us dietitians to teach you the truth. Resources:,polysaccharides%20are%20considered%20complex%20carbohydrates ( ) Clemens RA et al. Functionality of Sugars in Foods and Health. Comprehensive Reviews in Food Science and Food Safety 2016: Vol 15, 433-470