Metabolic and immune systems are among the most fundamental requirements for survival. These two processes are highly integrated, and the proper function of each is dependent on the other
A Drosophila is an ideal model to research human diseases including diabetes and cardiovascular diseases, in a recent study on the relationship between a high sugar diet and the innate immune response in Drosophila, flies were fed with a high-sucrose diet and observed defects in the phagocytosis of pathogen cells. High-sucrose diet-induced negative alterations in immune cells and aberrant activation of the innate immune system, including inflammation.
Gut bacteria also play a key role in the development of innate immune cells – specifically macrophages, monocytes and neutrophils – special white blood cells that provide the first line of defense against invading pathogens.
High sugar content in the diet was found to cause changes in the composition of gut bacteria, especially a decrease in bacterial diversity and abundance of Bacteroidetes and an increase in the abundance of harmful Proteobacteria. At the same time, the intestinal mucosa showed inflammatory changes and impaired resistance.
So, evidence suggest that processed, simple sugars reduce white blood cell phagocytosis – defense against pathogens – and increase inflammatory cytokine markers in the blood inducing disorders of the immune system and stimulating chronic inflammation.
Is sugar still your choice?
Cardiovascular or heart diseases are the primary cause of premature deaths, particularly in developing countries. Blood lipid disorders, including low levels of high-density lipoprotein cholesterol and high levels of triacylgycerols and low-density lipoprotein cholesterol, constitute a crucial risk factor for cardiovascular diseases. Such adverse changes in blood lipid parameters may result from excessive consumption of simple sugars such as monosaccharides and disaccharides, which are added more and more frequently to foodstuffs for technology and flavor purposes.
The American Heart Association recommends limiting the amount of added sugar consumed to no more than 100 calories per day for women and 150 calories per day for men, which equates to about 5% of the daily discretionary calorie allowance. But for most of the population meets these requirements seems to be impossible.
Numerous studies link high sugar intake with adverse changes in lipoproteins. Several studies have shown an inverse association between dietary sucrose and high-density lipoprotein cholesterol (HDL). HDL cholesterol is known as the “good” cholesterol because it helps remove other forms of cholesterol from your bloodstream. Higher levels of HDL cholesterol are associated with a lower risk of heart disease and high sugar intake significantly lowers HDL cholesterol thus increasing cardiovascular disease risk.
Furthermore, a diet high in sucrose (>20% of energy) is associated with an elevation of plasma triglyceride concentrations. This increase is due to both increased hepatic secretion and impaired clearance of very-low-density lipoprotein. An increase in the triglyceride concentration is exposed to a higher risk of CVD events.
High blood pressure is another risk factor for cardiovascular disease such as myocardial infarction, heart failure, stroke, and renal failure. In numerous studies rats were given a sucrose solution instead of water to drink, showing that in some period of time their systolic blood pressure was elevated. Sucrose consumption stimulates the sympathetic system. Studies have shown that glucose intake can also significantly raise cytosolic free calcium concentrations in vascular smooth muscle cells. Increases in vascular smooth muscle calcium concentrations are associated with vasoconstriction and vascular resistance, which can increase blood pressure. A 15-years study found that people who got 17% to 21% of their calories from added sugar had a 38% higher risk of dying from cardiovascular disease compared to those who consumed 8% of their calories as added sugar. Obesity, hypertension and dyslipidemia induced by high sugar intake are significant cardiovascular disease factors, which are persistent as well in patients with diabetes.
It has been estimated that there are over one billion individuals worldwide who are currently obese and by the year 2030 this number is going to rise to 1.5 billion individuals if current trend continues. Obesity was initially seen primarily in the wealthy countries, who would have been the only ones able to afford sugar, for example the rise in sugar intake in United Kingdom and United States closely correlates with the rise in obesity rates observed in these countries. Furthermore, the later introduction of sugar to developing countries also correlates with the later rise in their rates of obesity and comorbidities.
Nowadays it is an obesity pandemic. In the USA, it has been estimated that 33.8 % of adults, over 66 million individuals, are obese, while an additional 74 million are overweight. It is estimated that the prevalence of obesity grew a shocking 40 % over the last 30 years. In European countries, obesity ranges from 20 to 30% and the rates are even higher in Australia, South America, and the Middle East. Numerous studies linked the ingestion of added sugars to obesity. Why?
Unhealthy dietary habits, alone or in combination with other lifestyle-related factors can provide a ground for obesity. In most countries, dietary habits have been gradually changed from traditional to Westernized diets that contain a substantial amount of meat, high fat content, and sweet foods including desserts and sugar-sweetened beverages. Mice fed fructose-sweetened water gain more weight than do mice given the same calories as starch, which suggests that fructose may also slow the basal metabolic rate. So, fructose specifically does not stimulate insulin secretion or the production of the hormone (leptin) regulating long-term food energy balance, such that sugar tends not to satisfy the appetite and affects glucose metabolism, lipid profile and insulin resistance.
Any food with added sugars is calorie dense food without any nutrient value – no vitamins, minerals, fiber, protein, and fat. Pure simple carbohydrates… Proteins, fat, complex carbohydrates, fiber are necessary nutrients not only for wellbeing but also for an appropriate level of satiety in order not to consume an excessive amount of food.
Clinical studies have confirmed that sucrose intake (particularly fructose) can induce weight gain. Serum triacylglycerols (fatty substances transported in the blood in the form of lipoproteins) increased in young men who received a diet supplemented with 200 g sucrose per day, whereas concentrations did not increase when starch was the primary carbohydrate. Numerous studies have shown that patients with obesity have decreased taste perception, particularly for sweet tastes. A similar hypothesis has been proposed regarding evidence for reduced brain dopamine receptors in obesity and, in both cases, it is proposed that increased food consumption, and associated weight gain, resulting from the need to increase sensory and brain stimulation. There is also pre clinical evidence in rodents and fruit flies that dietary sugar content influences sweet taste perception. For example, in Drosophila melanogaster a high sugar diet led to the decreased response of ‘sweet taste sensing neurons’, resulting in diminished behavioral responses to sweet tastes. Importantly, reduction of sweet taste responses through neural manipulation resulted in overfeeding and obesity, further suggesting that sweet taste perception is a driver of obesity.
So, an association between sugar and obesity is likely to be attributed to multiple factors such as intake of a considerable amount of energy, less feeling of fullness, decreased taste perception, and reduced brain dopamine receptors, stimulating insulin secretion, and fat storage following the long-term consumption of sugar.