Sugar or rather sweet items is some thing that everyone cherishes. A little bit in cakes, chocolates, mousse who doesn’t like sweet taste.
However, lately the kind of review scientists and nutritionists are presenting about sugar kind of makes rethink my choice of sugar as great food but that still doesn’t stop me from eating it (in moderation though).
If I were to animate sugar in my mind, it would be a cute sugar block that sprinkles magic and life in every food item but the current day scenario of sugar and weight gain makes me think of it as a villain in a black trench coat with an evil smile invading every foodstuff possible!
So what’s the fuss with sugar and metabolic diseases?
Table of Contents
- Why do we need sugars?
- Glucose and its Evil twin Fructose
- 5 Ways Sugar Causes Weight Gain
- 1. Sugar provides empty calories
- 2. Fructose impairs liver functioning
- 3. Sugars impair the functioning of hormone insulin
- 4. Fructose upsets the appetite hormones
- 5. Sugar is addictive
- Added sugar vs. Natural sugar: What’s good? What’s bad?
- Natural and artificial sweeteners- Are they good substitutes for table sugar?
- Is sugar alone the culprit behind the obesity epidemic?
Why do we need sugars?
Sugars belong to the family of carbohydrates. They comprise of carbon, hydrogen and oxygen and consist of different units of carbohydrates.
Simple sugars are monosaccharides and consist of glucose, fructose and galactose. These combine with each other to form disaccharides such as sucrose (table sugar), maltose and lactose.
Sugars are extracted from sugar cane and sugar beet and refined and marketed in various forms.
Table sugar has an energy content of 3.94 kilocalories per gram and sugar consumption has increased up to 25.1 kg on average per person per year which would be around 270 calories per day.
WHO recommends that daily intake of free sugars should account for 5% calories. So for a person with calorie requirement of 2000 calories this would mean 100 calories and we are definitely exceeding the limit.
So why do we need sugars in the first place? Because it’s a form of instant energy. Most carbohydrates are digested and broken down into simple sugars like glucose and fructose.
Some body tissues can derive energy from fats and proteins but cells like brain cells and blood cells utilise only glucose as energy sources.
Glucose and its Evil twin Fructose
Glucose is a source of energy that can be easily tapped by the body. It is digested easily and absorbed from the intestines to the bloodstream.
Insulin and glucagon are two hormones that control blood glucose levels. Insulin transports glucose to liver where if glucose is in excess is stored as glycogen and used as an energy reserve in case of starvation. Glucagon does the opposite. It signals the liver to synthesize glucose.
Fructose does not work this way. Fructose occurs naturally in fruits and vegetables. It is used as high fructose syrup to prepare corn syrup that is added to sodas and other beverages.
Average American obtains fructose from sodas and not from fruits. Fructose is poorly absorbed in the intestines.
Also it cant be utilised as a direct source of energy since cells do not have the protein that is required to allow fructose inside. That’s why glucose is taken up readily by cells in compared to fructose.
So the only organ that is set on the mission to metabolize fructose is the liver. Fructose enters glucose metabolism at a step that has crossed the steps where glucose metabolism can be controlled.
The liver therefore does not control its metabolism and actively converts into fats which circulate in the blood or is stored in fat tissue. Now this is what causes the weight gain.
Also sugars are empty calories, that is they do not provide any nutrients and it’s their caloric content which could be the reason behind weight gain.
5 Ways Sugar Causes Weight Gain
So what exactly happens inside our body once we ingest sugar? A review study covering a large number of clinical trials and cohort studies evaluated the effect of dietary sugars on body weight.
Reduced intake of sugars was associated with decrease in body weight while increased consumption led to increase in body weight.
Sugar sweetened beverages increased the odds of developing obesity. Overall inclusion of free sugars is considered as a determinant of body weight.
1. Sugar provides empty calories
There are 4 calories per gram of sugar. So if a product has 15g of sugar you are consuming 60 calories per serving from sugar.
Any product that contains milk or fruit will have natural sugars but there are added sugars too which go with the names like:
• Brown sugar
• Corn syrup, High fructose corn syrup
• All words that have sugar or –ose in the end (fructose, maltose)
Also products come with claims which mean:
• Sugar free- Less than 0.5 g of sugar per serving
• Reduced sugar- At least 25% less sugar than traditional serving
• No added sugars- No sugars or sugar containing material
• Low sugar- Not defined
AHA recommends 100 calories (6 teaspoons of sugar) for women and 150 calories (9 teaspoons) for men while WHO recommends 5% of calorie intake should be from free sugars.
2. Fructose impairs liver functioning
As mentioned previously fructose has a different mechanism of metabolism. At low levels fructose along with glucose, glycogen reserves are replenished in liver and muscles.
However high fructose diet stimulates lipogenesis or lipid production in the liver and also causes insulin resistance. Liver prefers production of fats from fructose rather than storing it as glycogen.
A study on healthy postmenopausal women demonstrated that for every 1cup/day increase in sugar sweetened beverages and 10g/day increase in added sugar and fructose liver enzymes increased thus indicating the risk of fat production in liver.
High fructose or high sucrose diet leads to production of fats, high levels of glucose and impaired antioxidant balance which mark the onset of fatty liver disease.
3. Sugars impair the functioning of hormone insulin
Whenever we think of insulin we are reminded of diabetes which is a condition where impaired insulin levels affect glucose metabolism.
Glucose does not affect insulin levels that significantly to cause loss of function. But a high fat diet can stimulate insulin resistance and high insulin and glucose levels together can contribute to insulin resistance.
So what exactly is insulin resistance? When cells stop responding to insulin thats when insulin resistance occurs. Insulin has another activity apart from regulating glucose levels.
It regulates storage of fats in fat tissue and stimulates release of fats in the blood. Elevated insulin levels lead to increased storage of energy as fat rather than stimulating its burning.
Also another phenomenon occurs. High blood glucose levels after eating sugary foods leads to increased production of insulin. This lowers glucose levels to an extent where the appetite is stimulated again leading to overeating.
4. Fructose upsets the appetite hormones
Leptin and ghrelin are two hormones that participate in energy balance. Leptin is slow acting; it reduces energy intake and stimulates energy expenditure.
Ghrelin on the other hand stimulates hunger and reduces satiety.
Leptin is a hormone that is secreted by fat tissues. It is secreted in proportion to the fat present in your body and signals the brain to reduce intake and burn the fat instead.
In obesity leptin levels increase but cells don’t respond to it leading to leptin resistance. Fructose contributes to leptin resistance and in normal individuals it impairs the activity of both ghrelin and leptin.
Fructose’s inability to suppress ghrelin can explain why it does not promote most meal post meal satiety like glucose.
A study was conducted to evaluate the effects of high fructose and high glucose diet on leptin, ghrelin and insulin. 12 normal weight women were asked to consume meals with 30% calories from high fructose and high glucose sweetened beverages.
Insulin and leptin responses were reduced significantly after a high fructose diet than high glucose diet. Oddly high fructose diet did not suppress ghrelin response as well as high glucose.
Ghrelin and leptin signal the nervous system and regulate energy balance, therefore the results of this study that fructose can decrease leptin, increase ghrelin levels and increase caloric intake leading to obesity.
5. Sugar is addictive
In fact the experimental study on animals shows that rats exposed to sucrose diet develop a addiction to it, have reduced satiety and their brain releases dopamine more than normal animals.
Dopamine is a chemical secreted by the brain that regulates its pleasure and reward centers.
Repeated, excessive sugar intake is found to alter the levels of dopamine and opiods( a chemical that reduces signals of pain being sent to the brain).
Astonishingly, animal studies show that sucrose dependant animals experience anxiety and imbalance in brain chemicals similar to that experienced by morphine withdrawal.
This explains why we just seem to get over our sugar cravings.
Note: Sugar causes weight gain by supplying empty calories, causing insulin and leptin resistance, affecting lipid metabolism in liver. Also it causes an addiction thus paving the way for overeating.
Added sugar vs. Natural sugar: What’s good? What’s bad?
Added sugar is the refined and processed sugar that is available to you for cooking purposes. It is void of nutrients.Thus it provides us empty calories- it is void of nutrients.
Sugar sweetened beverages like sodas, energy drinks and sports drinks are the biggest sources of added sugar in an average American’s diet. Other important sources include cookies, cakes, pastries, and similar treats; fruit drinks; ice cream, frozen yogurt and the like; candy; and ready-to-eat cereals.
Sugar sweetened beverages contain added high fructose syrup and we know that fructose gets readily converted to fats in our body. Consumption of sugar sweetened beverages is associated with weight gain and unhealthy dietary pattern in adults as well as children.
However this is not the case with natural sources of sugar. Fruits, vegetables, nuts and grains contain sugars.Such sugars are present in unison with a number of nutrients such as minerals, vitamins, fibre etc.
So when consumed as part of whole food, other nutrients especially fibre cause slow absorption of sugar there by reducing its impact on blood sugar levels.
A study presenting the health risks linked with fructose states that these risks are not applicable to fruits and vegetables. Also fruits and vegetables do not cause weight gain.
Results of a 12 year study demonstrated that increased intake of fruits and vegetables reduces the risk of developing obesity by 24%.
Note: Fructose in fruits is not harmful like that present in processed sugar as fruits provide you with a number of nutrients that allow slow absorption of sugar and reduce its effect on insulin.
Natural and artificial sweeteners- Are they good substitutes for table sugar?
Low calorie sweeteners are thought of as alternative to table sugar. The aim is to maintain sweetness but reduce calorie intake.
A meta analysis of studies examining the effect of low calorie sweeteners on body weight reflect modest decrease in weight and can be used as tools for weight management.
Reduced calories reduce energy density of the food. Energy density is number of calories per unit weight of the food item. Low energy density foods are less palatable. However this is not the case with sweet foods.
So despite of using low calorie sweeteners to reduce energy density, the palatability remains unaffected and some studies raise a question whether these sweeteners have a long term control on appetite. Else it defeats the purpose of replacing sugar in the first place.
Artificial sweeteners include aspartame, saccharine, stevia, sucralose and sugar alcohols. These are low in calories but there is not much evidence regarding their effect on appetite and subsequent weight gain.
Sugar alcohols do not disturb insulin levels but are difficult to digest.
Among the natural sweeteners, raw honey seems to be the best. It consists of 40% glucose, 36% fructose, and 24% other sugars. Despite of containing fructose the combination of fructose and glucose makes it easier to digest.
Maple syrup contains fructose but also some good minerals and molasses also provides you with nutrients, but whether those nutrients really quantify to significant health benefits is still a question.
Agave nectar is a very popular natural sweetener but in reality it is highly processed and contains 90% fructose.
Note: Among the artificial sweeteners, stevia could be viable option especially if you could use stevia leaves and for natural sweeteners honey is a great substitute for table sugar. Again moderation is advised.
Is sugar alone the culprit behind the obesity epidemic?
Though most of the studies suggest that increased intake of sugar leads to weight gain, some researchers do not agree with this point.
High sugar intake disrupts lipid metabolism and is linked with gallstone formation.
An animal study focused on this point commented that it is not the sugar in the high sucrose diet that reduces production of bile acid rather it is the reduced content of fibre and fat which causes it.
A study on normal weight individuals shows that sucrose is more satiating than artificially sweetened drinks and it controls appetite, thus reducing energy intake and weight gain.
In a survey evaluating the relationship between dietary fat, sugar intake and BMI in British adults that the only sugar items that led to increased BMI in women were high fat sweet foods.
However sugar intake was inversely associated with BMI in men, thus demonstrating that gender differences could also play a role in compensation for weight gain due to sugar intake.
Vincent et. al bring some clarity on this confusion via their paper ‘Misconceptions about fructose-containing sugars and their role in the obesity epidemic’. They suggest that studies are mechanistic in their approach by using excessive amounts of isolated fructose which is obviously going to cause metabolic defects.
Also studies correlating increased fructose consumption from added sugars with increase in obesity, focus on food disappearance data which is also food availability or market supplies and not the food consumption.
Thereby they indicate that both studies are limited in their approach. Via a thorough review of literature they have come to a conclusion that ‘fructose, as commonly consumed in mixed carbohydrate sources, does not exert specific metabolic effects that can account for an increase in body weight.’
Also they indicate that public health recommendations focused only on lowering sugar intake without any lifestyle changes are impractical. Also energy consumption or excessive calorie intake, even from sugar sweetened beverages where fructose is the main ingredient, cannot be ignored.
Considering all the information points in the opposite direction, it may be difficult to accept the points put forward by these researchers but this is definitely food for thought!
Also it depends on certain physiological features as to how one’s body might react. Moderate amount of sugar is easily metabolised by active people while sedentary individuals will gain weight.
Similarly if one suffers from insulin resistance or is lactose intolerant, he will have problem digesting sugar and consequently gain weight.
All we can say is that probably at moderate levels sugar might not lead to weight gain. However high consumption of sugar or fructose sweetened food items definitely cause weight gain or high consumption of fat rich and sugar foods will lead to weight gain. (Read Is Overeating An Addiction?)
Note: Sugar can contribute to weight gain when eaten in excess but can’t be solely blamed for obesity epidemic. Overconsumption of calories, differences in metabolism and gender differences should be accounted for the resultant weight gain.
Sugars are an immediate source of energy and also an essential ingredient, so it would be inappropriate to label it as toxic. Anything in excess could be deleterious and the same applies to sugar.
The amount, the source as well as the body type of the individual consuming sugar affects its impact on body weight. Quitting sugar does ensure reduced calorie load but quitting sugar can guarantee weight loss only if replaced by nutritive sources such as fruits and incorporating healthy changes in diet, lifestyle and eating habits.
We would say that an occasional however monitored indulgence in sugary items would be harmless especially if you are adhering to a low calorie diet and regular exercise.