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The simple truth about sugar

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Aaron Deere is a sports nutritionist, functional medicine consultant and advanced personal trainer. He is based in London.

Sugar has been implicated in causing serious health problems such as obesity, diabetes and heart disease. The list of complications seems endless, but without this most simple of carbohydrates our bodies would not be able to function properly.

Sugar, in the form of glucose, has many important roles in the body, including being the preferred energy source for muscle contraction and biologic work. More importantly, the brain requires glucose as its primary energy source. A lack of glucose can result in weakness and dizziness, and low blood-glucose levels – known as hypoglycaemia – and even death in severe cases[1].

Natural sugars
There are three types of sugars found naturally in foods. They are polysaccharides, such as starch and amylose, which are found in grains; monosaccharides, such as glucose, fructose and galactose, which are found in fruit; and disaccharides, such as sucrose, lactose or maltose, which are found in milk. These types of sugar come from foods which are beneficial to your diet because of the other compounds they contain.
Once these sugars are consumed they are broken down into the monosaccharide glucose in the gastrointestinal tract. There it is absorbed in the small intestine, enters the bloodstream and then travels to the liver.

Glucose is then transported by the bloodstream to the organs and other tissues, including the muscles and the brain, for use as energy. If it is not needed it is stored as glycogen in the liver and skeletal muscles.
If glycogen stores are already full then glucose is bio-transformed – through a process called de novo lipogenesis – and stored as fat[2].

Sugar mountain
With so many healthy foods containing natural sources of sugar, and it being essential to many biological functions, why is sugar being increasingly linked to such a long list of health problems? The answer is simple. It’s the sheer volume of the white stuff that we are consuming.

Because it is used as an additive to add sweetness and palatability to so many products, especially fast food, confectionary, fizzy drinks and convenience meals, it can be all too easy to consume huge amounts of added sugars in our diets. Most Americans today consume an average of an additional 22g of sugar per day above the recommended daily guidelines of 36g for men and 24g for women[3].

Sugar rush
Most added sugars are in the form of sucrose. When this disaccharide is broken down during digestion the result is a molecule of glucose and a molecule of fructose. If the liver’s storage capacity if full then the excess fructose is converted and stored as fat[4].

Fructose has also been shown to induce much less activity in satiety centres of the brain and left subjects feeling hungrier[5]. Over time this can result in an increased calorific intake, because the calories from sucrose are no longer so fulfilling which could create a cycle of overconsumption of sucrose and a constant state of positive energy balance. Not surprisingly, a strong statistical association has been shown between people who consumed the highest amounts of added sugar and rates of obesity, for all age groups[6].

One of the most damaging effects of excessive sugar consumption on health is the development of insulin resistance, a condition that occurs when the body produces insulin but can not use it effectively, so glucose remains in the bloodstream instead of being absorbed by the cells. Over time the insulin-producing beta cells of the pancreas cease to function, so blood glucose levels rise above normal ranges. This results in type-2 diabetes, and consistently high blood-glucose levels also damages nerves and blood vessels and can lead to serious health issues such as heart disease and kidney failure.

Training fuel
The consumption of sugar around training can have a direct effect upon physiological adaptations. Sugar intake can have a direct effect upon the expression of the enzyme AMPK, which plays a role in cellular energy homeostasis, effectively acting as the cell fuel gauge by detecting the level of energy (glycogen) within the cell. When cellular energy levels drop below a predetermined level, AMPK is activated to conserve energy by turning off energy-consuming anabolism and switching on catabolism, which ultimately improves energy efficiency and the ‘fitness’ of the cell.

Exercise has been shown to promote mitochondrial adaptations – the mitochondria are essentially the cell’s battery – but when AMPK was present the rate of mitochondrial biogenesis is increased.
This is significant to know if your goal is to reduce body-fat levels because mitochondrial adaptations will result in the potential for increased fat oxidation levels within the cells, but the consumption of sugar pre-workout can have a direct and negative impact on this.

Recovery rates
However, glycogen replenishment plays a key role in exercise recovery and research suggests that carbohydrate intake between 550g to 625g per day was found to restore muscle glycogen stores to pre-exercise levels within 22 hours, with carb consumption within a two-hour window immediately after training resulting in the highest rates of replenishment[7]. If rapid recovery post exercise is of importance – such as when you might be training twice per day – consuming carbohydrates in the from of simple sugars immediately after training is essential.

1 Strachan, M. W., Deary, I. J., Ewing, F. M., Ferguson, S. S., Young, M. J., & Frier, B. M. (2001). Acute hypoglycemia impairs the functioning of the central but not peripheral nervous system. Physiology & behavior, 72(1), 83-92.
2 Schwarz, J. M., Neese, R. A., Turner, S., Dare, D., & Hellerstein, M. K. (1995). Short-term alterations in carbohydrate energy intake in humans. Striking effects on hepatic glucose production, de novo lipogenesis, lipolysis, and whole-body fuel selection. Journal of Clinical Investigation, 96(6), 2735.
3 Malik, V. S., Schulze, M. B., & Hu, F. B. (2006). Intake of sugar-sweetened beverages and weight gain: a systematic review. The American journal of clinical nutrition, 84(2), 274-288.
4 Faeh, D., Minehira, K., Schwarz, J. M., Periasamy, R., Park, S., & Tappy, L. (2005). Effect of fructose overfeeding and fish oil administration on hepatic de novo lipogenesis and insulin sensitivity in healthy men. Diabetes, 54(7), 1907-1913.
5 Page, K. A., Chan, O., Arora, J., Belfort-DeAguiar, R., Dzuira, J., Roehmholdt, B.& Sherwin, R. S. (2013). Effects of fructose vs glucose on regional cerebral blood flow in brain regions involved with appetite and reward pathways.JAMA, 309(1), 63-70.
6 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. The American journal of clinical nutrition, 79(4), 537-543.
7 Ivy, J. L. (1991). Muscle glycogen synthesis before and after exercise. Sports Medicine, 11(1), 6-19.


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