Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, board-certified in Anesthesiology, Pain Medicine, Interventional Pain Management, Addiction Medicine and Obesity Medicine. Dr. Padda is the owner of Communicare Elite. Last reviewed August 8, 2026. How we produce and review this content.
In the San Antonio Longitudinal Study of Aging, which followed 749 older adults for several years, diet soda drinkers gained roughly three times as much waist circumference as non-drinkers. The study was observational, so it does not show that diet soda causes the gain.
Obesity is a genuine problem in later life, and older adults face a particular version of it: mobility limits make exercise harder, dental and swallowing problems narrow food choices, and fixed incomes narrow them further. Low- and zero-calorie products look like an obvious solution, and diet soda is the most popular of them.
Is diet soda linked to a bigger waist in older adults?
The San Antonio Longitudinal Study of Aging followed 749 older adults over several years, recording diet soda consumption and measuring waist circumference. The results were published in the Journal of the American Geriatrics Society.
Diet soda drinkers showed substantially greater increases in waist circumference than non-drinkers — roughly three times the expansion over the study period. Waist circumference matters independently of overall weight: abdominal fat is more strongly linked to cardiovascular disease, type 2 diabetes and sleep apnea than fat elsewhere on the body.
Does diet soda cause weight gain?
This is observational, and the obvious alternative explanation is hard to rule out: people who are already gaining weight, or who already have a diagnosis like diabetes, are precisely the people who switch to diet soda. The drink may be a marker of the problem rather than a cause of it.
Proposed mechanisms exist — effects on gut bacteria, on appetite regulation, on the learned relationship between sweetness and calories — but none is settled. What can be said fairly is that swapping to diet soda has not been shown to deliver the benefit people expect from it.
Are “diet” foods actually healthier?
Diet soda is a specific case of a general pattern. Products marketed on the absence of one ingredient — sugar-free, fat-free, low-carb — tend to be judged healthy on that basis alone, and the substitution often turns out to deliver less than expected. For older adults the stakes are slightly different from the usual weight-loss framing: the risk is not only excess but displacement, where low-nutrition products crowd out food carrying the protein, fiber and micronutrients an aging body needs more of, not less.
Someone eating too little protein while drinking three diet sodas a day has a nutrition problem that no amount of calorie counting will identify.
What this means for day-to-day care. Two practical notes. First, plain water is genuinely underrated: dehydration in older adults contributes to confusion, constipation, urinary infections and falls, and many people simply drink too little because getting to the bathroom is difficult. Making fluids easy to reach helps more than switching brands. Second, this is the person’s own home and their own choice — an attendant’s job is to support what they want, not to police their groceries.
Frequently asked questions
Does switching to diet soda help you lose weight?
Switching has not been shown to deliver the benefit people expect. In the San Antonio Longitudinal Study of Aging, which followed 749 older adults for several years, diet soda drinkers gained roughly three times as much waist circumference as people who did not drink it. The study was observational, so it links diet soda to waist gain without proving the drink caused it.
Why does waist size matter more than weight?
Waist circumference tracks abdominal fat, and abdominal fat is more strongly linked to cardiovascular disease, type 2 diabetes and sleep apnea than fat stored elsewhere on the body. That is why waist size tells you more than the number on the scale, and why the San Antonio researchers measured it directly over several years.
What is the problem with diet drinks for older adults?
For older adults the bigger risk is displacement. Low-nutrition products can crowd out foods that carry the protein, fiber and micronutrients an aging body needs more of, not less. Someone eating too little protein while drinking three diet sodas a day has a nutrition problem that no amount of calorie counting will catch.
What should older adults drink instead of diet soda?
Plain water is underrated. Dehydration in older adults contributes to confusion, constipation, urinary infections and falls, and many people drink too little because getting to the bathroom is hard. Keeping fluids within easy reach helps more than switching brands. It is still the person’s own home and choice, and a caregiver’s role is to support it.
Sources
- Journal of the American Geriatrics Society — 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
- World Health Organization — Obesity and overweight
- Mayo Clinic — Belly fat: why weight loss matters
This article is general information, not medical advice. It describes published research; it is not a recommendation for you or the person you care for. Never start, stop or change a prescribed medication because of something you read here — talk to the prescribing clinician first. Communicare Elite provides non-medical personal care through Missouri’s Consumer Directed Services program and does not provide medical advice or treatment.