Science on weight gain and obesity related issues
Industry science
Is “diet” deceptive marketing?
Scientific references

Aspartame, one of the world’s most popular sugar substitutes, is found in thousands of sugar-free, low-sugar and so-called “diet” drinks and foods. Yet the scientific evidence described in this fact sheet links aspartame to weight gain, increased appetite, diabetes, metabolic derangement and obesity-related diseases.

See also our companion fact sheet, Aspartame: Decades of Science Point to Serious Health Risks, with information about the peer-reviewed studies linking aspartame tocancer, cardiovascular disease, Alzheimer’s disease, strokes, seizures, shortened pregnancies and headaches.

Quick facts

• Aspartame — also marketed as NutraSweet, Equal, Sugar Twin and AminoSweet — is a widely used artificial sweetener found in thousands of food and beverage products, including Diet Coke and Diet Pepsi, sugar-free gum, candy, condiments and vitamins.
• Aspartame is known in the European Union as E 951.
• The FDA has said aspartame is “safe for the general population under certain conditions.” Many scientists have said the FDA approval was based on suspect data and should be reconsidered.
• Dozens of studies conducted over decades link aspartame to serious health problems.
• In May 2023, the World Health Organization advised people to avoid non-sugar sweeteners, including aspartame, for weight control.

Aspartame: Weight gain and obesity related issues

A July 2023 study in the International Journal of Obesity reports that long-term intake of aspartame and saccharin are related to greater volumes of visceral, intermuscular, and subcutaneous adipose tissue. In addition, total artificial sweetener, saccharin, aspartame, and diet beverage intakes were associated with greater body mass index, body weight, waist circumference, and their increases over a 25-year period. The study is based on a validated diet history questionnaire administered at baseline, year 7, and year 20 examinations in 3,088 men and women enrolled in the Coronary Artery Risk Development in Young Adults cohort (CARDIA).

Several reviews of the scientific literature on artificial sweeteners suggest that they do not contribute to weight loss, and instead may cause weight gain.

• A 2017 meta analysis of research on artificial sweeteners, published in the Canadian Medical Association Journal, found no clear evidence of weight loss benefits for artificial sweeteners in randomized clinical trials, and reported that cohort studies associate artificial sweeteners with “increases in weight and waist circumference, and higher incidence of obesity, hypertension, metabolic syndrome, type 2 diabetes and cardiovascular events.”¹See also
  • “Artificial sweeteners don’t help with weight loss and may lead to gained pounds,” by Catherine Caruso, STAT (7.17.2017)
  • “Why one cardiologist has drunk his last diet soda,” by Harlan Krumholz, Wall Street Journal (9.14.2017)
  • “This cardiologist wants his family to cut back on diet soda. Should yours, too?” byDavid Becker, M.D., Philly Inquirer (9.12.2017)

• A 2013 Trends in Endocrinology and Metabolism review article finds “accumulating evidence suggests that frequent consumers of these sugar substitutes may also be at increased risk of excessive weight gain, metabolic syndrome, type 2 diabetes, and cardiovascular disease,” and that “frequent consumption of high-intensity sweeteners may have the counterintuitive effect of inducing metabolic derangements.”²
• A 2009 American Journal of Clinical Nutrition review article finds that the “addition of NNS [nonnutritive sweeteners] to diets poses no benefit for weight loss or reduced weight gain without energy restriction. There are long-standing and recent concerns that inclusion of NNS in the diet promotes energy intake and contributes to obesity.”³
• A 2010 Yale Journal of Biology and Medicine review of the literature on artificial sweeteners concludes that, “research studies suggest that artificial sweeteners may contribute to weight gain.”⁴
• A 2010 International Journal of Pediatric Obesity review article states, “Data from large, epidemiologic studies support the existence of an association between artificially-sweetened beverage consumption and weight gain in children.”⁵

Epidemiological evidence suggests that artificial sweeteners are implicated in weight gain. For example:

• The San Antonio Heart Study “observed a classic, positive dose-response relationship between AS [artificially sweetened] beverage consumption and long-term weight gain.” Furthermore, it found that consuming more than 21 artificially sweetened beverages per week – compared to those who consumed none, “was associated with almost-doubled risk” of overweight or obesity.”⁶
• A study of beverage consumption among children and adolescents aged 6-19 published in International Journal of Food Sciences and Nutrition found that “BMI is positively associated with consumption of diet carbonated beverages.”⁷
• A two-year study in of 164 children published in the Journal of the American College of Nutrition found that “Increases in diet soda consumption were significantly greater for overweight and subjects who gained weight as compared to normal weight subjects. Baseline BMI Z-score and year 2 diet soda consumption predicted 83.1% of the variance in year 2 BMI Z-score.” It also found that “Diet soda consumption was the only type of beverage associated with year 2 BMI Z-score, and consumption was greater in overweight subjects and subjects who gained weight as compared to normal weight subjects at two years.”⁸
• The U.S. Growing Up Today study of more than 10,000 children aged 9-14 found that, for boys, intakes of diet soda “were significantly associated with weight gains.”⁹
• A 2016 study in the International Journal of Obesity reported finding seven tentatively replicated factors showing significant associations with abdominal obesity in women, including aspartame intake.¹⁰
• People who regularly consume artificial sweeteners are at increased risk of “excessive weight gain, metabolic syndrome, type 2 diabetes, and cardiovascular disease,”¹¹according to a 2013 Purdue review over 40 years published in Trends in Endocrinology & Metabolism

Other types of studies similarly suggest that artificial sweeteners do not contribute to weight loss. For example, interventional studies do not support the notion that artificial sweeteners produce weight loss. According to the Yale Journal of Biology and Medicine review of the scientific literature, “consensus from interventional studies suggests that artificial sweeteners do not help reduce weight when used alone.”¹²

Some studies also suggest that artificial sweeteners increase appetite, which may promote weight gain. For example, the Yale Journal of Biology and Medicine review found that “Preload experiments generally have found that sweet taste, whether delivered by sugar or artificial sweeteners, enhanced human appetite.”¹³

Studies based on rodents suggest that consumption of artificial sweeteners can lead to consuming extra food. According to the Yale Journal of Biology and Medicine review, “Inconsistent coupling between sweet taste and caloric content can lead to compensatory overeating and positive energy balance.” In addition, according to the same article, “artificial sweeteners, precisely because they are sweet, encourage sugar craving and sugar dependence.”¹⁴

A 2014 study in the American Journal of Public Health found that “Overweight and obese adults in the United States drink more diet beverages than healthy-weight adults, consume significantly more calories from solid food—at both meals and snacks—than overweight and obese adults who drink SSBs [sugar-sweetened beverages], and consume a comparable amount of total calories as overweight and obese adults who drink SSBs.”¹⁵

A 2015 study of older adults in the Journal of the American Geriatrics Society found “In a striking dose-response relationship,” that “increasing DSI [diet soda intake] was associated with escalating abdominal obesity…”¹⁶

An important 2014 study published in Nature found that “consumption of commonly used NAS [non-caloric artificial sweetener] formulations drives the development of glucose intolerance through induction of compositional and functional alterations to the intestinal microbiota … our results link NAS consumption, dysbiosis and metabolic abnormalities … Our findings suggest that NAS may have directly contributed to enhancing the exact epidemic that they themselves were intended to fight.”¹⁷

Diabetes and metabolic derangement

Aspartame breaks down in part into phenylalanine, which interferes with the action of an enzyme intestinal alkaline phosphatase (IAP) previously shown to prevent metabolic syndrome, which is a group of symptoms associated with type 2 diabetes and cardiovascular disease. According to a 2017 study in Applied Physiology, Nutrition and Metabolism, mice receiving aspartame in their drinking water gained more weight and developed other symptoms of metabolic syndrome than animals fed similar diets lacking aspartame. The study concludes, “IAP’s protective effects in regard to the metabolic syndrome may be inhibited by phenylalanine, a metabolite of aspartame, perhaps explaining the lack of expected weight loss and metabolic improvements associated with diet drinks.”¹⁸

• See also: Mass General press release on the study, “Aspartame may prevent, not promote, weight loss by blocking intestinal enzyme’s activity”

People who regularly consume artificial sweeteners are at increased risk of “excessive weight gain, metabolic syndrome, type 2 diabetes, and cardiovascular disease,” according to a 2013 Purdue review over 40 years published in Trends in Endocrinology & Metabolism.¹⁹

In a study that followed 66,118 women over 14 years, both sugar sweetened beverages and artificially sweetened beverages were associated with risk of Type 2 diabetes. “Strong positive trends in T2D risk were also observed across quartiles of consumption for both types of beverage … No association was observed for 100% fruit juice consumption,” reported the 2013 study published in American Journal of Clinical Nutrition.²⁰

Intestinal dysbiosis, metabolic derangement and obesity

Artificial sweeteners can induce glucose intolerance by altering the gut microbiota, according to a 2014 study in Nature. The researchers wrote, “our results link NAS [non-caloric artificial sweetener] consumption, dysbiosis and metabolic abnormalities, thereby calling for a reassessment of massive NAS usage … Our findings suggest that NAS may have directly contributed to enhancing the exact epidemic [obesity] that they themselves were intended to fight.”²¹

• See also: “Artificial Sweeteners May Change our Gut Bacteria in Dangerous Ways,” by Ellen Ruppel Shell, Scientific American (4.1.2015)

A 2016 study in Applied Physiology Nutrition and Metabolism reported, “Aspartame intake significantly influenced the association between body mass index (BMI) and glucose tolerance… consumption of aspartame is associated with greater obesity-related impairments in glucose tolerance.”²²

According to a 2014 rat study in PLoS ONE, “aspartame elevated fasting glucose levels and an insulin tolerance test showed aspartame to impair insulin-stimulated glucose disposal … Fecal analysis of gut bacterial composition showed aspartame to increase total bacteria…”²³

Industry science

Not all recent studies find a link between artificial sweeteners and weight gain. Two industry-funded studies did not.

• A 2014 American Journal of Clinical Nutrition meta-analysis concluded that “Findings from observational studies showed no association between LCS [low-calorie sweetener] intake and body weight or fat mass and a small positive association with BMI [body mass index]; however, data from RCTs [randomized controlled trials], which provide the highest quality of evidence for examining the potentially causal effects of LCS intake, indicate that substituting LCS options for their regular-calorie versions results in a modest weight loss and may be a useful dietary tool to improve compliance with weight loss or weight maintenance plans.” The authors “received funding to conduct this research from the North American Branch of the International Life Sciences Institute (ILSI).”²⁴

The International Life Sciences Institute, a nonprofit that produces science for the food industry, is controversial among public health experts due to its funding from chemical, food and pharmaceutical companies and potential conflicts of interest, according to a 2010 article in Nature.²⁵See also:U.S. Right to Know fact sheet about the International Life Sciences Institute.

A series of stories published in UPI in 1987 by investigative reporter Greg Gordon describe ILSI’s involvement in directing research on aspartame toward studies likely to support the sweetener’s safety.

• A 2014 study in the journal Obesity tested water against artificially sweetened beverages for a 12-week weight loss program, finding that “water is not superior to NNS [non-nutritive sweetened] beverages for weight loss during a comprehensive behavioral weight loss program.” The study was “fully funded by the American Beverage Association,”²⁶which is the main lobbying group for the soda industry.

There is strong evidence that industry-funded studies in biomedical research are less trustworthy than those funded independently. A 2016 study in PLOS One by Daniele Mandrioli, Cristin Kearns and Lisa Bero examined the relationship between research outcomes and risk of bias, study sponsorship and author financial conflicts of interest in reviews of the effects of artificially sweetened beverages on weight outcomes.²⁷The researchers concluded, “Artificial sweetener industry sponsored reviews were more likely to have favorable results than non-industry sponsored reviews … as well as favorable conclusions.” Financial conflicts of interest were not disclosed in 42% of the reviews, and reviews performed by authors with financial conflicts of interest with the food industry (whether disclosed or not) were more likely to have favorable conclusions for the industry than reviews performed by authors without financial conflicts of interest.

A 2007 PLOS Medicine study on industry support for biomedical research found that “Industry funding of nutrition-related scientific articles may bias conclusions in favor of sponsors’ products, with potentially significant implications for public health … scientific articles about commonly consumed beverages funded entirely by industry were approximately four to eight times more likely to be favorable to the financial interests of the sponsors than articles without industry-related funding. Of particular interest, none of the interventional studies with all industry support had an unfavorable conclusion…”²⁸

Is “diet” deceptive marketing?

In April 2015, US Right to Know petitioned the Federal Trade Commission (FTC) and the Food and Drug Administration (FDA) to investigate the marketing and advertising practices of “diet” products that contain a chemical linked to weight gain.

We argued that the term “diet” appears to be deceptive, false and misleading in violation of section 5 of the Federal Trade Commission Act and section 403 of the Federal Food, Drug and Cosmetic Act. The agencies have so far declined to act citing lack of resources and other priorities (see FDA and FTC responses).

“It’s regrettable that the FTC won’t act to halt the deceptions of the ‘diet’ soda industry. Ample scientific evidence links artificial sweeteners to weight gain, not weight loss,” said Gary Ruskin, co-director of U.S. Right to Know. “I do believe that ‘diet’ soda will go down in U.S. history as one of the greatest consumer frauds ever.”

News coverage:

• “Soda Shouldn’t Be Called ‘Diet, ’ Advocacy Group Says,” by Greg Gordon, McClatchy (4.9.2015)
• “Diet” Soda Fraud?, byRiëtte van Laack, FDA Law Blog (4.19.2015)
• “FTC Declines to Probe Whether Ads for Diet Products are Deceptive,” by Greg Gordon, McClatchy (10.14.2015)

USRTK press releases and posts:

• Is “Diet” Soda a Fraud? We Asked FTC to Investigate, April 9, 2015
• Are Coke and Pepsi Lying to You About “Diet” Soda? April 9, 2015
• Is it Accurate to Call a Soda “Diet,” Consumer Group Asks Soda CEOs, May 20, 2015
• Is Coke Illegally Claiming “Diet” Soda is a Treatment for Obesity? July 1, 2015
• FTC Declines to Act Against Deceptive “Diet” Soda Ads, Oct. 14, 2015

Scientific references

[1] Azad, Meghan B., et al.Nonnutritive sweeteners and cardiometabolic health: a systematic review and meta-analysis of randomized controlled trials and prospective cohort studies.CMAJJuly 17, 2017vol. 189no. 28doi:10.1503/cmaj.161390 ( abstract / article)

[2]Swithers SE, “Artificial Sweeteners Produce the Counterintuitive Effect of Inducing Metabolic Derangements.” Trends in Endocrinology and Metabolism, July 10, 2013. 2013 Sep;24(9):431-41. PMID: 23850261. ( abstract / article)

[3] Mattes RD, Popkin BM, “Nonnutritive Sweetener Consumption in Humans: Effects on Appetite and Food Intake and Their Putative Mechanisms.” American Journal of Clinical Nutrition, December 3, 2008. 2009 Jan;89(1):1-14. PMID: 19056571. ( article)

[4] Yang Q, “Gain Weight by ‘Going Diet?’ Artificial Sweeteners and the Neurobiology of Sugar Cravings.” Yale Journal of Biology and Medicine, 2010 Jun;83(2):101-8. PMID: 20589192. ( article)

[5] Brown RJ, de Banate MA, Rother KI, “Artificial Sweeteners: a Systematic Review of Metabolic Effects in Youth.” International Journal of Pediatric Obesity, 2010 Aug;5(4):305-12. PMID: 20078374. ( abstract / article)

[6] Fowler SP, Williams K, Resendez RG, Hunt KJ, Hazuda HP, Stern MP. “Fueling the Obesity Epidemic? Artificially Sweetened Beverage Use and Long-Term Weight Gain.” Obesity, 2008 Aug;16(8):1894-900. PMID: 18535548. ( abstract / article)

[7] Forshee RA, Storey ML, “Total Beverage Consumption and Beverage Choices Among Children and Adolescents.” International Journal of Food Sciences and Nutrition. 2003 Jul;54(4):297-307. PMID: 12850891. ( abstract)

[8] Blum JW, Jacobsen DJ, Donnelly JE, “Beverage Consumption Patterns in Elementary School Aged Children Across a Two-Year Period.” Journal of the American College of Nutrition, 2005 Apr;24(2):93- 8. PMID: 15798075. ( abstract)

[9] Berkey CS, Rockett HR, Field AE, Gillman MW, Colditz GA. “Sugar-Added Beverages and Adolescent Weight Change.”Obes Res. 2004 May;12(5):778-88. PMID: 15166298. ( abstract / article)

[10] WWulaningsih, MVan Hemelrijck, K KTsilidis, ITzoulaki, CPatel and SRohrmann. “Investigating nutrition and lifestyle factors as determinants of abdominal obesity: an environment-wide study.” International Journal of Obesity (2017) 41, 340–347; doi:10.1038/ijo.2016.203; published online 6 December 2016 ( abstract / article)

[11] Susan E. Swithers, “Artificial sweeteners produce the counterintuitive effect of inducing metabolic derangements.” Trends Endocrinol Metab. 2013 Sep; 24(9): 431–441.

[12] Yang Q, “Gain Weight by ‘Going Diet?’ Artificial Sweeteners and the Neurobiology of Sugar Cravings.” Yale Journal of Biology and Medicine, 2010 Jun;83(2):101-8. PMID: 20589192. ( article)

[13] Yang Q, “Gain Weight by ‘Going Diet?’ Artificial Sweeteners and the Neurobiology of Sugar Cravings.” Yale Journal of Biology and Medicine, 2010 Jun;83(2):101-8. PMID: 20589192. ( article)

[14] Yang Q, “Gain Weight by ‘Going Diet?’ Artificial Sweeteners and the Neurobiology of Sugar Cravings.” Yale Journal of Biology and Medicine, 2010 Jun;83(2):101-8. PMID: 20589192. ( article)

[15] Bleich SN, Wolfson JA, Vine S, Wang YC, “Diet-Beverage Consumption and Caloric Intake Among US Adults, Overall and by Body Weight.” American Journal of Public Health, January 16, 2014. 2014 Mar;104(3):e72-8. PMID: 24432876. ( abstract / article)

[16] Fowler S, Williams K, Hazuda H, “Diet Soda Intake Is Associated with Long-Term Increases in Waist Circumference in a Biethnic Cohort of Older Adults: The San Antonio Longitudinal Study of Aging.” Journal of the American Geriatrics Society, March 17, 2015. ( abstract / article)

[17] Suez J. et al., “Artificial Sweeteners Induce Glucose Intolerance by Altering the Gut Microbiota.” Nature, September 17, 2014. 2014 Oct 9;514(7521):181-6. PMID: 25231862 ( abstract)

[18] Gul SS, Hamilton AR, Munoz AR, Phupitakphol T, Liu W, Hyoju SK, Economopoulos KP, Morrison S, Hu D, Zhang W, Gharedaghi MH, Huo H, Hamarneh SR, Hodin RA. “Inhibition of the gut enzyme intestinal alkaline phosphatase may explain how aspartame promotes glucose intolerance and obesity in mice.” Appl Physiol Nutr Metab. 2017 Jan;42(1):77-83. doi: 10.1139/apnm-2016-0346. Epub 2016 Nov 18. ( abstract / article)

[19] Susan E. Swithers, “Artificial sweeteners produce the counterintuitive effect of inducing metabolic derangements.” Trends Endocrinol Metab. 2013 Sep; 24(9): 431–441. ( article)

[20] Guy Fagherazzi, A Vilier, D Saes Sartorelli, M Lajous, B Balkau, F Clavel-Chapelon. “Consumption of artificially and sugar-sweetened beverages and incident type 2 diabetes in the Etude Epidémiologique auprès des femmes de la Mutuelle Générale de l’Education Nationale–European Prospective Investigation into Cancer and Nutrition cohort.” Am J Clin Nutr. 2013, Jan 30; doi: 10.3945/ ajcn.112.050997 ajcn.050997. ( abstract / article)

[21] Suez J et al. “Artificial sweeteners induce glucose intolerance by altering the gut microbiota.” Nature. 2014 Oct 9;514(7521). PMID: 25231862. ( abstract / article)

[22] Kuk JL, Brown RE. “Aspartame intake is associated with greater glucose intolerance in individuals with obesity.” Appl Physiol Nutr Metab. 2016 Jul;41(7):795-8. doi: 10.1139/apnm-2015-0675. Epub 2016 May 24. ( abstract)

[23] Palmnäs MSA, Cowan TE, Bomhof MR, Su J, Reimer RA, Vogel HJ, et al. (2014) Low-Dose Aspartame Consumption Differentially Affects Gut Microbiota-Host Metabolic Interactions in the Diet-Induced Obese Rat. PLoS ONE 9(10): e109841. ( article)

[24] Miller PE, Perez V, “Low-Calorie Sweeteners and Body Weight and Composition: a Meta-Analysis of Randomized Controlled Trials and Prospective Cohort Studies.” American Journal of Clinical Nutrition, June 18, 2014. 2014 Sep;100(3):765-77. PMID: 24944060. ( abstract / article)

[25] Declan Butler, “Food Agency Denies Conflict-of-Interest Claim.” Nature, October 5, 2010. ( article)

[26] Peters JC et al., “The Effects of Water and Non-Nutritive Sweetened Beverages on Weight Loss During a 12-Week Weight Loss Treatment Program.” Obesity, 2014 Jun;22(6):1415-21. PMID: 24862170. ( abstract / article)

[27]Mandrioli D, Kearns C, Bero L.”Relationship between Research Outcomes and Risk of Bias, Study Sponsorship, and Author Financial Conflicts of Interest in Reviews of the Effects of Artificially Sweetened Beverages on Weight Outcomes: A Systematic Review of Reviews.” PLOS One, September 8, 2016. https://doi.org/10.1371/journal.pone.0162198

[28] Lesser LI, Ebbeling CB, Goozner M, Wypij D, Ludwig DS. “Relationship Between Funding Source and Conclusion Among Nutrition-Related Scientific Articles.” PLOS Medicine, 2007 Jan;4(1):e5. PMID: 17214504. ( abstract / article)