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鈥淗ow sweet it is!鈥� was comedian Jackie Gleason鈥檚 catchphrase on his Saturday night variety program in the 1950s, usually delivered after a joke had landed. When he went on to star in The Honeymooners, a sitcom filmed before a live audience in what would later become the Ed Sullivan Theater, he would often use the phrase to acknowledge applause during the curtain call. Obviously 鈥渟weet鈥� was associated with delight.
Have you wondered why that should be so? Why do we crave sweets? Why are candies a reward for children鈥檚 good behaviour, which they should not be? Why do our mouths water at the thought of a slice of Esterhazy cake (look it up)? One theory is that in early human history food was scarce and sweet foods were not only a quick source of calories, but also signalled safety since toxic substances are often bitter.
There may also be a biochemical reason for our love of sweets. Sugar stimulates the release of dopamine, the so-called 鈥減leasure chemical,鈥� in the brain. You can also throw in the release of endorphins, the body鈥檚 natural stress-reducing opioid-like substances. Then there is the fact that the brain relies mostly on glucose for energy and less glucose entering the bloodstream stimulates the production of the hunger hormone ghrelin by cells in the protective mucous membrane that lines the stomach. Add to this that sweet foods are associated with happy moments such as birthdays and holidays, and we have a reasonable rationale for our love of sweets.
Today it is not difficult to indulge in that love affair because sugar is everywhere. It is added to our cereals, ice cream, yogurt, sodas, salad dressings and even ketchup. Interestingly, the easy availability of sugar is a relatively recent phenomenon. Although sugar cane was cultivated in Asia even before the Common Era, in Europe sugar was a rare luxury used mostly as medicine, grown in Sicily and the Iberian Peninsula where the climate was suitable. Only after plantations were established in America, thanks to Christopher Columbus bringing sugar-cane seedlings to the New World, did sugar become more readily available in Europe. By the mid-18th century, it had become a valuable import requiring a large labour force for production that tragically led to the mass kidnapping and enslavement of millions of Africans.
As the price of sugar dropped, consumption continued to increase until today; the average person in the west consumes about 70 grams (17 teaspoons) of added sugar a day. The American Heart Association recommends no more than nine teaspoons for men, six for women and less than six for children. That is in response to the overwhelming evidence that has emerged linking excess sugar consumption to obesity, type 2 diabetes, heart disease, fatty liver disease, dental caries, gout and metabolic syndrome. There is also growing evidence for links to certain cancers, dementia and mood disorders.
鈥淎dded sugar鈥� does not include sugars, mainly sucrose, glucose and fructose, that naturally occur in fruits and vegetables. These foods also contain fibre and water that slow digestion allowing glucose to enter the bloodstream more gradually, preventing spikes in blood glucose. Then there are the minerals, vitamins and 鈥減hytochemicals鈥� such as polyphenols in plant products that contribute to sound nutrition. Natural sugars in fruits and vegetables satisfy sweetness and satiety, while refined added sugars can actually intensify cravings because they trigger a quick dopamine 鈥渉it鈥� without causing a feeling of fullness. Sugar-sweetened beverages and candies allow for hundreds of calories to be consumed without feeling full, which reinforces repeated cravings. When added sugar is combined with fat, salt and flavourings, as in highly processed foods, there is an increase in palatability that has been associated, albeit somewhat controversially, with addiction due to provoking a surge in dopamine.
Concerns about the risks of sugar consumption have led to a booming market for artificial, or 鈥渘on-nutritive,鈥� sweeteners such as saccharin, aspartame, sucralose, acesulfame-potassium and stevia. These substances are hundreds of times sweeter than sucrose and can be added to foods and beverages in very small amounts to provide sweetness without adding calories. What they do provide is controversy.
The motivation for the development of these sweeteners was the elimination of calories from sugar with a view towards improved weight control. However, long-term studies have shown that swapping sugar for artificial sweeteners has little effect on weight. Some studies have even shown that these sweeteners increase the desire for sweets, explaining why they do not lead to weight loss. There are also allegations of carcinogenicity, particularly concerning aspartame, but the evidence is underwhelming. Some epidemiological studies have linked sweeteners with strokes, heart disease and type 2 diabetes, but here we encounter the spectre of 鈥渞everse causation.鈥� People with various aliments are more likely to switch to artificial sweeteners.
Now another concern has arisen. A study published in the journal Neurology by Brazilian researchers found a link between consuming more artificial sweeteners and cognitive decline. The term 鈥渓ink鈥� is always problematic because it speaks of correlation and can never prove a cause-and-effect relationship. In this case, people who consumed the highest amounts of any of six artificial sweeteners also had the greatest decline in thinking and memory as shown by standard tests. The decline was estimated to be roughly equivalent to 1.6 years of additional brain aging. Especially concerning was that the 鈥渉ighest amount鈥� consumed per day was the equivalent of one can of diet soda. Consider that a certain high-ranking American politician apparently drinks 12 diet sodas a day.
There are several issues about this study that followed some 12,000 subjects for eight years, with cognitive tests administered on average every three years. Food and beverage intake was based on a single dietary questionnaire at the beginning that asked about the consumption of specific foods over the previous year. Such assessments are notoriously unreliable, as is the assumption that the subjects followed the same diet for eight years. Another curious finding was that the link between artificial sweeteners and poorer cognition only existed for people under the age of 60. That is difficult to rationalize.
Then there is the question of how chemicals of totally different molecular structure, like the six sweeteners studied, would have the same biological effect. One possible explanation is that they disturb the gut microbiome, the population of bacteria in our digestive tract. There is accumulating evidence that certain bacteria can stimulate nerve endings in the gut, sending signals that influence mood, appetite and stress. Therefore, influencing cognition may not be that far-fetched. Several previous studies have indeed shown that artificial sweeteners can affect the microbiome but not always the same way.
Where does this leave us? If it is a choice between a diet sugar-sweetened soda, I would go for the diet drink based on the evidence for the dangers of excess sugar consumption. But the best decision is to choose water instead of either one. It may not be sweet, but makes for a sweeter life. If water could sing, it would go for Marvin Gaye鈥檚 1964 song How Sweet It Is To Be Loved By You, which, believe it or not, was inspired by Jackie Gleason鈥檚 quip.
