Diet Coke has the signature Coca-Cola flavor without the sugar and calories. However, Diet Coke and other diet colas may have some undesirable side effects.

Since Diet Coke was introduced in 1982, it has been marketed to — and consumed by — calorie-conscious people trying to cut sugar and lose weight. This soft drink has the Coca-Cola flavor without the sugar and calories, making it one of the most popular diet sodas on the market today. However, Diet Coke and other diet colas may have some undesirable side effects. Read on to understand that facts about these beverages.

Side Effects of Caffeine

Diet Coke is a source of caffeine, a widely-consumed stimulant also found in coffee and tea. However, a 12-ounce can of Diet Coke contains only 46 mg of caffeine, which easily falls below the 400-milligram limit set by the U.S. Food and Drug Administration (FDA).

If you consume too much caffeine, or if you are sensitive to the effects of this stimulant, you can experience side effects such as anxiety, jitters and poor sleep. Caffeine withdrawal can also be a problem if you suddenly reduce or stop drinking diet colas, coffee or other caffeine-containing drinks.

Diet Soda and Dehydration

Diet Coke and other caffeinated beverages are widely thought to be dehydrating, since caffeine is a mild diuretic — meaning it increases urination. However, a research review found this diuretic effect only occurred with doses of 250 to 300 mg of caffeine, and the increased urination did not occur in regular consumers of caffeinated beverages. Since Diet Coke is mostly water, drinking it will help hydrate the body. In fact, even regular coffee has been shown to hydrate the body in a manner similar to water.

Effects on Bone Health

Frequent consumption of cola drinks is also thought to negatively impact bone health. In fact, cola beverages have been linked to lower bone mineral density in postmenopausal women. While the mechanism of action is unclear, common theories are related to coke's caffeine and phosphorus content.

Caffeine is known to decrease the amount of calcium in bones, but this effect is considered negligible if dietary calcium intake is adequate and the daily intake of caffeine is below 400 mg.

In addition, too much phosphorus coupled with a low calcium intake can reduce the amount of calcium the bones absorb. However, there are no experimental studies that specifically link the phosphorus in colas to poor bone health.

Weight and Health Side Effects

Although diet sodas are favored by people trying to lose weight and reduce sugar intake, there's inconsistent data to prove these low-calorie beverages help with weight loss. In fact, some research has linked frequent consumption of diet sodas to metabolic syndrome, a cluster of abnormalities — including elevated blood sugars, high blood pressure and abnormal cholesterol levels — which increase the risk of cardiovascular disease.

The reason for these ill effects isn't clear, but animal studies have shown that artificial sweeteners can negatively impact gut bacteria, and some researchers suspect these diet drinks might interfere with the body's natural ability to manage energy balance and appetite. Despite these concerns, an August 2018 statement from the American Heart Association suggests that diet soft drinks may be a helpful replacement for sugar-sweetened beverages in the diet 5.

Side Effects of Aspartame

Diet Coke is sweetened with aspartame, commonly known as Nutrasweet, although other diet soft drinks may be sweetened with acesulfame potassium, sucralose or derivatives of the sweet-tasting plant, stevia.

Some people report side effects such as headaches, digestive distress and mood changes with aspartame use, although one small study demonstrated no apparent sensitivity and no physical or psychological effects with consumption of this sweetener.

When the FDA approved aspartame in 1981, over 100 studies supported its safety and the FDA set an acceptable daily intake (ADI) equivalent of 75 packets a day -- significantly less than the average intake 810. Despite this, ongoing concerns and rumors persist about its safety.

While more research is needed to understand the role of aspartame in health, medical organizations including the American Heart Association and the American Diabetes Association still consider moderate use of diet sodas acceptable as a short-term replacement for sugar-sweetened beverages 5. For most people, however, water is the optimal beverage.

Warnings and Precautions

If you have any questions about the risks or benefits of diet colas, or if you experience any side effects from drinking diet colas, seek guidance from your doctor or dietitian. If you have phenylketonuria (PKU), a rare genetic disorder in which the body can’t process the amino acid phenylalanine, you'll need to avoid Diet Coke and other sources of aspartame since these products are a source of phenylalanine.

Reviewed by Kay Peck, MPH RD