Key Points - In a substantial observational study, women consuming over two diet beverages daily exhibited higher rates of stroke, heart disease, and overall mortality. The risk of stroke was especially pronounced among obese and Black women. - The assessment of diet beverage consumption was conducted only once, limiting the ability to track changes over time. Intake from foods or single-serving packets was not evaluated. - Observational studies cannot establish causation, and this study had various limitations, such as potential inaccuracies in dietary reporting, reverse causation, and insufficient differentiation between types of low- and no-calorie sweeteners. - While this study adds to the existing knowledge regarding diet beverages and health outcomes, caution is advised in interpreting the findings. More comprehensive long-term randomized controlled trials are necessary.

A new investigation featured in the journal Stroke has garnered attention for its analysis of self-reported consumption of low- and no-calorie sweetened beverages, termed "diet drinks," and their implications for cardiovascular health. As such studies attract media coverage, essential details can sometimes be overlooked. Here’s an overview of the research findings.

Study Overview The primary aim of this research was to evaluate the link between diet beverages and the risk of cardiovascular issues, such as stroke, coronary heart disease, and mortality. This study was part of the extensive Women’s Health Initiative Observational Study, initiated in the 1990s to monitor the health of over 90,000 postmenopausal women aged between 50 and 79 at the outset. The current analysis focused on the diet drink habits of 81,714 women using a single food frequency questionnaire (FFQ) administered three years after their enrollment. Participants responded to one question about diet beverages, referring to a standard serving size of 12 ounces (equivalent to one can of soda): “In the past three months, how often did you consume these drinks?” The beverage types included low-calorie, artificially sweetened sodas and fruit drinks but excluded options like coffee or tea with sweeteners. No data was gathered on the specific types of sweeteners used. Responses were categorized into four groups: “never or less than once per week,” “1 to 4 times a week,” “5 to 7 times a week,” and “2 or more times per day.”

After an average follow-up period of nearly 12 years, researchers recorded incidents of various types of stroke, coronary heart disease, and deaths within the study group.

Research Findings The majority of participants (almost two-thirds of the over 80,000 women) were infrequent consumers (either never or less than once a week) of diet drinks, with only 5.1 percent consuming two or more daily (equivalent to 24 or more fluid ounces). Those who drank more diet beverages were generally younger, had higher education and income levels, reported increased energy intake, lower diet quality, and less physical activity, and had a history of diabetes, heart attack, or stroke. Additionally, they were more likely to be overweight or obese, report a smoking history (either current or past), and consume alcohol.

Compared to the least-frequent consumers of diet drinks, women who had two or more daily were found to have: - 23 percent higher risk of any type of stroke - 31 percent higher risk of ischemic stroke (stroke caused by a blood clot) - 29 percent higher risk of heart disease - 16 percent higher risk of mortality from any cause

These risk factors were assessed while accounting for numerous variables that could affect the outcomes, including age, smoking history, and high blood pressure. The risk of stroke was notably higher in obese and Black women who reported increased consumption of diet drinks compared to other racial groups, while White women with higher intake showed an increased risk of coronary heart disease.

Role of Food Frequency Questionnaires (FFQs) in Nutrition Studies FFQs, like the one used in this study, are crucial for obtaining insights into dietary patterns over time and their potential associations with health outcomes. However, they come with challenges. Many individuals struggle to accurately report their dietary intake, often underreporting less healthy foods and overreporting healthier options, misjudging serving sizes, or simply forgetting. Additionally, since participants were asked about their consumption only once, any changes in their habits over time were not captured. For instance, if a participant initially reported drinking one diet beverage daily and later altered that frequency, the study would not have recorded this shift.

Observational studies using FFQs can initiate critical discussions in scientific research but cannot establish direct cause-and-effect relationships. Instead, they can inform future experimental studies, like randomized control trials (RCTs), which are considered the benchmark in research design. A combination of observational and experimental data is essential for advancing knowledge in nutrition and food science.

Strengths and Limitations of the Study The study's strengths include its large participant pool and over a decade of follow-up. Researchers aimed to mitigate reverse causality by excluding women diagnosed with diabetes or cardiovascular issues before the FFQ. This approach was intended to prevent misattributing health problems as a result of diet drink consumption when it could be the opposite. However, editorial authors noted that this analysis could not fully eliminate the possibility of reverse causality, as they did not exclude participants with conditions like prediabetes, obesity, or metabolic syndrome—each of which is linked to cardiovascular disease development and could lead to a switch from sugar-sweetened beverages to diet drinks.

A significant limitation remains the study's observational nature. As discussed frequently, observational studies are unable to demonstrate direct causation (i.e., that diet drinks cause strokes or heart disease). Causal relationships can only be established through RCTs, which would assign participants to either consume diet beverages or a placebo and monitor the results. While some RCTs on diet drinks exist, they are often too brief to capture long-term health effects, indicating a need for more extensive studies.

Moreover, the methodology used to assess low- and no-calorie sweetener intake raised concerns. Data on beverage consumption was collected only once, posing challenges in tracking changes over time. As noted, self-reported dietary intake is often fraught with inaccuracies. Low- and no-calorie sweeteners are also present in various foods, including yogurts, nutrition bars, sauces, and candies, and are frequently added through single-serving packets. The study did not include comprehensive reporting on overall sweetener intake, thus limiting the evaluation of sweeteners' effects from both foods and drinks. Additionally, the lack of differentiation between types of low- and no-calorie sweeteners obscures understanding of how specific sweeteners might impact health outcomes.

Lastly, it's important to consider confounding variables and the generalizability of the findings. Since this study focused on postmenopausal women, the conclusions may not extend to other demographics, including men and younger women. While the researchers accounted for many influencing factors, additional unconsidered variables could also play a role, leaving room for residual confounding. For example, fluctuations in weight and dietary habits prior to the study may have been significant factors, as noted by editorial authors.

Final Thoughts The debate surrounding the role of beverages in our diets remains active within the nutrition field. The American Heart Association (AHA) has recently issued an advisory stating that insufficient scientific evidence exists to conclude whether diet drinks significantly alter heart disease and stroke risk factors. The AHA acknowledged that diet drinks might effectively replace high-calorie sugary beverages, yet recommends water as the optimal calorie-free choice. Similar advice was included in the 2015 U.S. Dietary Guidelines.

As independent researchers continue to explore low- and no-calorie sweeteners, regulatory bodies worldwide, including the U.S. Food and Drug Administration and the European Food Safety Authority, have reviewed them and deemed them safe.

As noted by the editorial authors, “Ongoing public health initiatives to decrease sugar-sweetened beverage consumption are wise. However, transitioning heavy consumers to water can be challenging.” Opting for diet drinks over full-calorie alternatives is one of several strategies individuals can utilize to manage added sugar consumption and control calorie intake—both crucial for minimizing the risk of diet-related diseases and promoting overall health.

This article was authored by Allison Webster, PhD, RD, with contributions from Kris Sollid, RD. It was first published on foodinsight.org.