A lot of us love sweet food. I’ve recently discovered sweet foods. They have this thing called “chocolate” now. Have you tried it? It’s AMAZING. The trouble is that sweet food often have a boatload of sugar (and often not much else!). Eating a lot of sugar can lead to obesity and obesity can lead to all sorts of awful things like diabetes. So how can we address this dangerous addiction? By fooling our tastebuds with chemistry, of course! Synthetic sweeteners are a good way of cutting down the caloric content of food and drinks – certainly favorable to (and sweeter than) high fructose corn syrup. Synthetic sweeteners are chemicals that give a strong sweet taste but don’t provide any calories (or, at least, very few) when ingested. They’re found mostly in diet foods and drinks.
There are 3 common synthetic sweeteners: aspartame, the closely related neotame, and sucralose. You may have heard from many sources that these sweeteners might pose some adverse health effects. Numerous studies have shown strong evidence that even at large doses of these chemicals, there are no adverse acute or chronic effects. I’ll cite some research articles to check out. This post will cover aspartame.
Aspartame (marketed originally as “NutraSweet” and now “AminoSweet”) is the oldest of the synthetic sweeteners, having been discovered in the early 60’s and used ever since. Aspartame is a dipeptide (a protein composed of two amino acids) composed of L-aspartic acid and the methyl ester of L-phenylalanine, both natural amino acids. It was, like many great scientific advances, discovered by accident when a researcher synthesized this dipeptide en route to the tetrapeptide hormone gastrin and licked a contaminated finger to turn a page. Aspartame is roughly 200 times sweeter than sucrose, which is ordinary sugar. The current best process for the synthesis of aspartame is accomplished enzymatically – the major components are coupled using an enzyme engineered to perform this task. In the body, aspartame is broken down into its constituents: aspartic acid, phenylalanine, and methanol.
These three constituents of aspartame are natural compounds. Aspartic acid is a natural amino acid that binds (weakly) to a neural receptor called the NMDA-receptor. This receptor is associated with development of the synapses in the brain, affecting memory and learning. Phenylalanine can be converted into tyrosine (another amino acid) in the body. Individuals with phenylketonuria cannot consume aspartame because they lack an enzyme that correctly converts phenylalanine to tyrosine. Finally, methanol is the smallest alcohol in existence with the formula CH3OH. Methanol is toxic but it is very rapidly flushed from the body in urine. You’ll find methanol in all sorts of commonly consumed drinks like fruit juices and alcoholic beverages, albeit in very low amounts.
The FDA projects a certain intake and determines the safety of the sweetener based on this projection. That intake assumes that ALL dietary sugar is replaced with the sweetener, about 22-34 mg per kg of bodyweight per day (mg/kg bw/day). That’s a huge overestimation! That’s roughly 10 cans of diet coke per day, or the amount of phenylalanine and aspartic acid found in 8 oz of milk or 3 oz of beef, or even the amount of methanol found in 8 oz of vegetable juice or 2 oz of gin (Franz, M. Diabetes Educator 1986 12:145–147).
A lot of controversy surrounded aspartame during its development. In the 90’s, safety studies on aspartame were questioned and many myths arose surrounding the development of lupus and multiple sclerosis due to the consumption of aspartame. These were summarily disproved and debunked – aspartame remains one of the most thoroughly studied and tested food additives and has been approved for safe consumption in over 90 countries. For a recent independent review on the safety of consumption of aspartame, see: Magnuson, B. A. et al. Critical Reviews in Toxicology 2007 37:629-727. The levels of aspartic acid and phenylalanine in blood plasma do not differ from measurements taken after a meal even at high doses of aspartame (Stegink, L. D. et al. Journal of Nutrition 1977 107:1837–1845). This is highly relevant to pregnant mothers and children. In addition, no adverse effects, either acute or chronic, on reproduction and development were noted in animal studies using doses as large as 4000 mg/kg bw/day (JECFA. Twenty-third Report of the Joint FAO/WHO Expert Committee on Food Additives (JECFA). 1980 World Health Organization, Geneva). These studies, conducted by independent labs or international organizations with no vested interests in the success or failure of aspartame, provide thorough evidence that this synthetic sweetener causes no ill effects in animals and humans.
This is where I’ll stop talking about aspartame for now. I’ve talked briefly about the discovery, structure, and synthesis of the molecule, as well as some of the safety issues (or lack thereof) regarding the intake of this artificial sweetener. I’ll discuss the other two sweeteners in subsequent posts. I’ll also discuss some of the misinformation regarding aspartame and similar chemicals – people were right to question these chemicals, but those questions have been answered. Now it’s time to question the questioners!
Diet Coke is By Evan-Amos via Wikimedia Commons
Wrigley’s Double Mint Gum is By Mgmoscatello via Wikimedia Commons