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Sugars are not essential nutrients, which means humans do not need to get them from foods to be healthy. All sugars you need can be produced in your body.
Picture 1. Examples of chemical formulas of two sugars:
Left: Glucose (a monosaccharide)
Right: sucrose (a disaccharide)
List of Sugars in Foods
- Monosaccharides (simple sugars):
Calories in Sugars
Sugars provide 3.5-4 kilocalories per gram , except isomaltose (<2 kcal/g)  and tagatose (1.5 kcal/g) .
One teaspoon (4 grams) of table sugar contains 15 Calories .
Are sugars “empty calories?”
In fact, calories from sugary foods are the same as calories from other foods. The term “empty calories” refers to low nutritional value of sugary foods (soda, sweets) in the sense that they are often low in vitamins and minerals.
Foods High in Sugars
Picture 2. Examples of foods high in sugars
Sugars naturally occur in high amounts only in plant foods, mainly in fruits and in much lower amounts in vegetables, nuts, legumes, cereals and milk. Sugars are added to certain commercial foods, beverages, medicinal syrups, pills and supplements.
Chart 1. FOODS HIGH IN SUGARS
SUGAR CONTENT (grams)
|Fresh (1 medium fruit): feijoa, grapefruit, guava, kiwifruit, melon (cantaloupe), nectarine, orange, papaya, peach, plums, pommegranate, rowal, tangerines||10-20|
|Fresh (1/2 cup): abiyuch, apricot, blueberries, cherries (sour, sweet), loganberries, mulberries, pineapple; watermelon (1 cup); jams (1 tbsp)||5-10|
Chart 1 sources: [2, 27]
Added sugars are sugars added during food processing. Added sugars may include anhydrous dextrose, brown sugar, confectioner’s powdered sugar, corn syrup, corn-syrup solids, crystal dextrose (glucose), fructose, galactose, high-fructose corn syrup (HFCS), honey, invert sugar, isomaltulose, lactose, malt syrup, maltose, maple syrup, molasses, nectars, pancake syrup, raw sugar, sucrose, tagatose, trehalose and white sugar [25-p.266;26].
Foods with no sugar (<1 g/serving) include unprocessed animal foods: meats, poultry, fish, eggs, butter and hard cheese (hard, mozzarella, pasteurized, ricotta). Oils also contain no sugars.
Vegetables, cereals, bagels, legumes, seeds, nuts, margarine, American, feta, cottage and cream cheese may contain up to 3 grams of sugar per serving.
Fruits that contain less than 5 grams of sugars per serving (1/2 cup, 117 mL): avocado, blackberries, clementines, cranberries, currants, eggplant, kumquat, lime, olives, raspberries, rhubarb, strawberries.
Sugars with Low Glycemic Index
Sugar alcohols (polyols), such as erythritol and xylitol also have low glycemic index.
Rules about claims about sugar content in commercial foods in the U.S. and EU [28-pp.305-6]:
- “Sugar-free” foods should contain less than 0.5 grams sugars per serving (in the U.S.) or per 100 g food (in the EU).
- “Low-sugar” foods should contain less than 5 grams sugars per 100 grams food or less than 2.5 grams sugars per 100 grams liquid (in the EU).
- “Reduced-sugar” foods should contain at least 25% less (in the U.S.) or 30% less sugars (in the EU) than regular foods.
Fermentable and Nonfermentable Sugars
Fermentable sugars can be fermented (broken down) by yeasts or bacteria.
Bacteria normally present in the human large intestine can ferment fructose, galactose, maltose, mannose, lactose, sucrose and tagatose into gases (hydrogen, carbon dioxide, methane), short-chain fatty acids (SCFAs) and other substances. From these sugars, usually only fructose and lactose, which may be slowly absorbed in the small intestine, actually reach the large intestine where bacteria break them down. Fructose and lactose are considered FODMAPs (fermentable oligo-, di- and monosaccharides and polyols), which can cause abdominal bloating, excessive gas (flatulence), loose stools or diarrhea in individuals with fructose malabsorption, lactose intolerance and irritable bowel syndrome (IBS).
Fructose, lactose and other fermentable sugars can also cause bloating in individuals with small intestinal bacterial overgrowth (SIBO).
Isomaltose is not fermentable by the intestinal bacteria.
Can sugar be bad for you?
The term sugar intolerance may include various disorders:
- Disorders with impaired sugar digestion or absorption resulting in abdominal bloating, excessive gas and diarrhea: fructose malabsorption and lactose intolerance. Diagnosis is confirmed by breath tests . Individuals with small intestinal bacterial overgrowth, celiac and Crohn’s disease can also experience symptoms after fructose and lactose ingestion.
- Hereditary fructose intolerance (HFI), a genetic disorder with impaired fructose metabolism.
- Genetic disorders: disaccharide intolerance or congenital sucrase isomaltase deficiency (CSID) with diarrhea in infants after sucrose or starch ingestion 
- Allergy to pure sugars is not known.
Sugars and Tooth Decay (Dental Caries)
The bacteria in mouth can break down certain sugars into acids, which can damage the enamel and thus cause tooth decay (dental caries) .
- Highly cariogenic sugars (in decreasing order): sucrose  trehalulose , glucose [30,31], fructose [30,31]
- Lowly cariogenic sugars: lactose [36,37], galactose , trehalose  and isomaltose [6,9].
- Non-cariogenic sugars: isomaltulose (palatinose) [10,34], sucralose , D-tagatose . Other sweeteners that do not promote dental caries and are as such approved by US Food and Drug Administration (FDA): xylitol, sorbitol, mannitol, maltitol, isomalt, lactitol, hydrogenated starch hydrolysates, hydrogenated glucose syrups and erythritol [6,10].
Frequent consumption of foods high in sugars, such as sweets, honey, soft drinks, fruit juices [12,13,14] and, according to some [15,16], but not all  studies, even fresh fruits, especially when they represent the main part of the diet , may promote dental caries.
Diet cola (without sugars) may also promotes dental caries [18,50]. The risk of dental caries may be reduced by using a straw positioned to the back of the mouth when drinking sugary beverages . Replacing sugary foods with starchy foods (bread, pasta, rice, potatoes) may not help, since starch can also promote dental caries [8,20]. It is the frequency of eating sugary foods and the time elapsed between a meal and tooth brushing rather than the amount of sugar consumed that may increase the risk of tooth decay .
According to one Cochrane review of studies the evidence for recommendation to change sugar intake to prevent caries is poor .
Weight gain. High sugar intake may be associated with weight gain [21,39]. It is not high intake of sugars alone but high calorie intake that can increase weight [40,42].
Diabetes mellitus type 2. In several systematic reviews of studies, high sugar intake was associated with significantly increased risk of diabetes 2 but the authors were not able to say if the increased risk was due to sugar intake itself or due to the associated weight gain [21,23,41,43]. Authors of the other 2 systematic reviews concluded that the risk of diabetes 2 is associated by the sugar intake itself, independently of weigh gain [53,54].
Blood pressure and heart disease. In several studies, high sugar intake was associated with high blood pressure [22,44] and increased risk of heart disease .
Sugar crash or reactive hypoglycemia. In individuals who had stomach surgery, food can pass quickly into the small intestine, which can result in quick glucose absorption, great increase of blood glucose levels followed by quick insulin release and the fall of glucose under normal levels (reactive hypoglycemia). Avoiding meals high in sugar can help prevent reactive hypoglycemia .
How much sugar is too much?
The U.S. Food and Drug Administration (FDA) and Institute of Medicine in the U.S. have not set any specific recommendations for sugar intake.
There is insufficient evidence about association between high sugar intake and acne , ADHD  or cancer .
Sugar Craving, Addiction and Withdrawal Symptoms
Sugar craving is an excessive desire to eat sugary foods. Causes may include (anecdotal reports): hunger, habit, sedentary life style, psychological or physical stress (exercise), depression, premenstrual syndrome (PMS), pregnancy , low-carb diet, hypoglycemia (low blood sugar), migraine, diabetes mellitus, disorders with loss of glucose with urine (hyperthyroidism, Cushing syndrome, acromegaly).
Sugar addiction is an irresistible craving for sugar. It was observed in some chronic alcoholics and in drug addicts .
Sugar withdrawal symptoms (anecdotal reports) may include headache, depression and insomnia.
What may help reduce sugar craving? You can try to be more active (if you have a sedentary life style), quit certain types of foods, such as sweetened beverages, and eat more filling, high-fiber foods. Switching from sugars to artificial sweeteners may not help.
Frequently Asked Questions
1. Do sugars have any health benefits?
Sugars provide about 4 Calories of energy per gram.
2. Which foods can I eat if I am on a low-sugar diet?
Unsweetened whole-grain breads and ready-to-eat-cereals without fruits, unsweetened vegetables, beans, peas and lentils, nuts (except chestnuts), seeds and unsweetened meats, poultry, fish and eggs.
Milk contains lactose, which is a sugar. White breads, pasta, rice and potatoes are similar to sugars, because glucose from them is quickly absorbed.
3. What is sugar detox diet?
Sugar detox diets are various diet plans that supposedly help you to eat less sugar. The term “detox” is misleading, since sugar is not toxic.