Soft drinks increase the risk of obesity and cardiovascular diseases. Sugar-sweetened drinks do this in four ways:
- Direct increase in calorie intake
- Appetite stimulation
- Negative effects of high-fructose corn syrup on metabolism
- Replacement of healthy dietary intake
Sugar based soft drinks usually contain about 140-150 calories per serving (12 oz). Therefore, if one adjusts dietary intake to account for these calories, weight gain in unlikely. However, what happens in most cases is that the dietary intake is not decreased while more than 400 calories are added through these sucrose-sweetened drinks. This was discovered in a study by DiMeglio and Mattes, who also reported that when a solid sugar supplement was used, in the form on jelly beans, people tended to reduce their dietary caloric intake to compensate. Other studies have corroborated these findings, suggesting that sugar-based drinks do not trigger satiety in the way solids do. However, the physiological basis of this difference is not yet known.
It has also been proposed that high glycemic carbohydrates that are absorbed quickly, such as sugar sweetened soft drinks, lead to a rapid change in the glucose or insulin levels, leading to appetite stimulation. Appetite stimulation occurs when the blood glucose level drops rapidly. Studies have also shown that in humans, increased hunger and calorie consumption is related to differences in the glycemic load intake or glycemic index as well as differences in the serum glucose and insulin levels.
On the other hand, studies have also shown that high fructose intake can promote obesity to a large extent than an equivalent amount of glucose. A study by Elliott et al demonstrated that fructose is metabolized preferentially into lipids by the liver, as compared to glucose. This study showed a link between fructose, weight gain and insulin resistance syndrome.
Fructose only has a limited impact on insulin-stimulation, which means that when we consume food or beverage that contains fructose, smaller amounts of insulin will be produced than an equivalent intake of glucose. In fact, a study on mice by Jurgens et al implied that soft drinks sweetened with fructose are more likely to increase adiposity than beverages that are either sugar sweetened or artificial sucrose sweetened.
Over the past few decades, the intake of milk has been decreasing, being replaced by sugar-sweetened soft drinks. This shift from milk to sweetened beverages has led to a decrease in the daily intake of calcium, zinc, magnesium, phosphorous, vitamin A and proteins. This finding was corroborated in children and adolescents by Harnack et al, while French et al found that soft drinks affected dietary quality because the youth is replacing milk consumption with these beverages. This actually increase in bone fracture and osteoporosis.