Individuals who consume a diet high in sodium (found in processed and junk food) or artificially sweetened drinks (usually 'diet' sodas) are more likely to experience a decline in kidney function, according to two papers presented at the American Society of Nephrology's annual meeting in California.
More than 3,000 women were studied to identify the impact of sodium and sweetened drinks on kidney function, and it was found that "while more study is needed, our research suggests that higher sodium and artificially sweetened soda intake are associated with greater rate of decline in kidney function."
The first study, "Associations of diet with Kidney Function Decline," examined the influence of individual dietary nutrients on kidney function decline over 11 years in more than 3,000 women. The authors found that "in women with well-preserved kidney function, higher dietary sodium intake was associated with greater kidney function decline, which is consistent with experimental animal data that high sodium intake promotes progressive kidney decline."
The second study, "Associations of Sweetened beverages with Kidney Function Decline," examined the influence of sugar-sweetened and artificially sweetened beverages on kidney function decline in the same group of participants. An analysis of these participants had previously reported an association between sugar-sweetened soda and urinary protein, but data on kidney function change was not available. This investigation reported "a significant two-fold increased odds, between two or more servings per day of artificially sweetened soda and faster kidney function decline; no relation between sugar-sweetened beverages and kidney function decline was noted."
This association persisted even after the study authors accounted for age, caloric intake, obesity, high blood pressure, diabetes, cigarette smoking, physical activity, and cardiovascular disease.
'Diet' or sugar-free versions of soft drinks usually contain artificial sweeteners, as well as food and drink labeled as 'no sugar'. A popular sweetener is the carcinogen aspartame. Many studies, including a 2005 study  have associated aspartame consumption to all sorts of illness and disease including cancerous tumors, lymphomas, lesions in various organs, nerve damage, seizures, and premature death.
Similarly sucralose, popularly marketed as the artificial sweetener derived from sugar, has been implicated in severe chronic illnesses including brain and nervous system disorders, migraine headaches, cancers, and immune-system debilitation.
Though touted as safe, the components of sucralose are verifiable toxins. Among other results, laboratory tests have concluded that long-term sucralose consumption shrinks the thymus gland, the biological source of the immune system. The popular sweetener Splenda is made from sucralose, and a 2008 study  found that this sweetener reduced the amount of good bacteria in the intestines by 50%, increased the pH level in the intestines, and contributed to increases in body weight.
Try to avoid or minimize your intake of these artificial sweeteners, which are not healthier or safer than sugar.
-  Soffritti M, et al. First Experimental Demonstration of the Multipotential Carcinogenic Effects of aspartame Administered in the Feed to Sprague-Dawley Rats. Environmental health Perspectives, 2005. http://www.sweetpoison.com/pdf/Soffritti_et_al_in_EHP.pdf
-  Abou-Donia MB, El-Masry EM, Abdel-Rahman AA, McLendon RE, Schiffman SS. Splenda alters gut microflora and increases intestinal p-glycoprotein and cytochrome p-450 in male rats. Journal of toxicology and environmental health. Part A 2008;71(21):1415-29.
- Swithers SE, Davidson TL. A Role for Sweet Taste: Calorie Predictive Relations in energy Regulation by Rats. Behavioral Neuroscience 2008, Vol. 122, No. 1, 161-173.