Having been a Diet Coke "addict" in my days of little sleep and low energy in medical school, I can attest to the attraction of diet sodas. Believe me that, as a doctor, I really hate it when they discover that one of my few vices could screw up my health. While I have since given up this particular vice, let me tell you, it wasn't easy.
Here's the most confusing part about diet soda: Many people drink it because they think that it's "healthier" than regular Coke (you know who you are, calorie-counters). But there are many negative health consequences associated with drinking too much Diet Coke; let's review what those are and how much Diet Coke is too much.
The one component of diet soda that separates it from the regular product is the artificial sweetener aspartame, which some researchers suspect may not be completely benign. According to the FDA, aspartame is associated with headaches, dizziness, loss of balance, mood swings, nausea, memory loss, muscle weakness, blurred vision, fatigue, skin rashes and joint and musculoskeletal pain. (That alone might make you want to order water with your meal, right?) Recent experiments using lab rats demonstrated adverse effects for concentrations well above normal human exposure, and some health professionals think that aspartame may pose health risks when consumed in large quantities.
But note that there is no scientific evidence whatsoever that consumption of aspartame at or below the FDA's Acceptable Daily Intake level carries any risk and therefore the side effects "associated" with aspartame cannot be considered "caused" by aspartame. Currently, the acceptable daily intake for aspartame is set at 50 mg/kg body weight in the United States, the equivalent of about 20 cans of Diet Coke a day for an adult weighing 165 pounds! (There are 180 mg of aspartame in a 12 oz can of diet soda).
Caffeine is the other draw to these waistline-friendly beverages. Diet Coke contains 46.5 mg of caffeine per can. Drinking more than 500 to 600 mg of caffeine a day (about four to seven cups of coffee or ten cans of Diet Coke), can cause restlessness, anxiety and headaches. Caffeine also acts as a diuretic, which makes Diet Coke potentially dehydrating. Other risks involved with drinking large amounts of caffeinated beverages include ulcers, headaches and possible decreased bone density.
Furthermore, excessive consumption of Diet Coke, which is high in phosphorus, can also deplete you of calcium and increase your chances of osteoporosis.
So, what's my advice? Cut back on the Diet Cokes if your caffeine consumption is above 200 mg a day, the amount found in approximately two cups of coffee or three to four 12 oz cans of caffeinated soda. And avoid artificial sweeteners as much as you can.