The question of whether soda consumption can increase the risk of cancer is complex, involving two separate lines of scientific inquiry: the effects of sugar and the potential impact of specific chemical additives. Public concern focuses equally on sugar-sweetened beverages (SSBs) and artificially sweetened, or “diet,” sodas. This review presents the current scientific evidence regarding these concerns, distinguishing between indirect metabolic effects and direct chemical hazards.
The Metabolic Link: Sugar, Weight Gain, and Increased Risk
The strongest established connection between soda and cancer risk is indirect, stemming from the high caloric load of sugar-sweetened beverages. SSBs are a major source of added sugars, which contribute significantly to excessive energy intake without promoting satiety. This high caloric density is a primary driver of long-term weight gain, overweight, and obesity.
Obesity is a well-established risk factor for at least 13 different types of cancer, including those of the colon, rectum, pancreas, liver, kidney, and postmenopausal breast. The mechanism involves several biological pathways that become dysregulated with excess body fat. Increased adipose tissue drives chronic, low-grade inflammation throughout the body, creating an environment that can promote tumor growth.
Excess sugar intake also leads to insulin resistance, a condition where cells respond poorly to insulin, forcing the pancreas to produce more of the hormone. High levels of insulin and insulin-like growth factors can directly stimulate the proliferation of cancer cells. Even after accounting for overall body mass index (BMI), some studies suggest that high SSB consumption is independently associated with an increased risk for certain cancers, such as colorectal and kidney cancer.
The sheer volume of rapidly absorbed sugar contributes to metabolic dysfunction. This includes the accumulation of visceral fat and altered lipid metabolism, further compounding the risk of chronic diseases that precede or promote cancer development. Therefore, the consumption of SSBs raises cancer risk primarily by fueling the epidemic of obesity and related metabolic disorders.
Specific Additives and Potential Carcinogens
Beyond the metabolic consequences of sugar, scientists have investigated certain non-sugar chemical components found in soda formulations for direct carcinogenic potential. One such chemical is 4-methylimidazole (4-MEI), which forms as a byproduct during the manufacture of Class III and Class IV caramel colorings. These colorings are widely used to give many sodas their distinctive brown hue.
Animal studies found that high-dose exposure to 4-MEI resulted in an increased incidence of certain lung tumors in mice. Based on this evidence, the International Agency for Research on Cancer (IARC) classified 4-MEI as “possibly carcinogenic to humans,” placing it in Group 2B. However, regulatory bodies emphasize that the doses used in these animal studies were far higher than human exposure levels from typical soda consumption.
Another chemical concern relates to the potential formation of benzene, a known human carcinogen, in certain beverages. Benzene can form when the preservative sodium or potassium benzoate interacts with ascorbic acid (Vitamin C). This reaction is accelerated by exposure to heat, light, and the presence of certain metal ions.
While benzene is a serious health hazard, the beverage industry has largely reformulated products since the early 1990s to mitigate its formation. The trace levels of benzene occasionally detected in sodas are typically well below the maximum contaminant level set for drinking water. Current scientific consensus suggests the direct risk from these specific additives in soda, at typical consumption levels, is low.
Distinguishing the Evidence on Artificial Sweeteners
The question of cancer risk in diet sodas, which use artificial sweeteners, presents a distinct area of study separate from sugar’s metabolic effects. Artificial sweeteners like aspartame, sucralose, and saccharin have been subject to intense scrutiny and safety reviews for decades. The debate recently intensified with the 2023 evaluation of aspartame by the World Health Organization (WHO).
The IARC classified aspartame as “possibly carcinogenic to humans” (Group 2B), based on limited evidence found in human and animal studies concerning hepatocellular carcinoma (liver cancer). The IARC classification identifies a potential hazard but does not quantify the actual risk to a person at normal exposure levels. For context, this Group 2B classification also includes agents such as aloe vera whole leaf extract.
Concurrently, the Joint Expert Committee on Food Additives (JECFA), a separate WHO body, reaffirmed the acceptable daily intake (ADI) for aspartame at 0–40 mg per kilogram of body weight per day. The JECFA concluded that the evidence of an association between aspartame consumption and cancer in humans was not convincing enough to alter the established safety limits.
Other common sweeteners, such as sucralose, have similarly undergone extensive testing and remain approved for use at specified levels by major regulatory agencies. The limited and often conflicting nature of the evidence means that while the hazard of aspartame has been noted, the actual cancer risk to the average consumer from diet soda is not considered a major concern by most public health bodies.
Regulatory Stance and Health Organization Guidance
Health organizations generally approach the cancer risk of soda by focusing on the public health threat posed by sugar-sweetened beverages. The American Cancer Society (ACS) recommends that individuals limit their consumption of sugary drinks, including sodas, sweetened fruit juices, and sports drinks. This guidance is primarily driven by the strong link between these beverages and weight gain, which is a significant factor in numerous cancers.
The ACS emphasizes that a healthy eating pattern to reduce cancer risk should focus on maintaining a healthy weight and avoiding excess body fat accumulation. Since SSBs contribute large amounts of empty calories and are associated with a higher risk of obesity-related cancers, their reduction is a clear public health priority.
For diet sodas and artificial sweeteners, the guidance is more nuanced, reflecting the separation between hazard identification and risk assessment. The dual finding from the WHO—IARC’s hazard classification and JECFA’s reaffirmation of the ADI—underscores that the risk at typical consumption levels is not currently deemed high enough to warrant a change in consumption advice. Therefore, the overall scientific consensus recommends minimizing or eliminating sugar-sweetened soda due to its proven metabolic effects, while acknowledging the ongoing scrutiny of certain additives and artificial sweeteners.