Do Sugary Drinks Cause Insulin Resistance? What a Controlled Trial Found

Not in seven weeks, and not in the way the phrase is usually thrown around — but something measurable does happen, and it happens in the liver.

In a double-blind randomized trial published in the Journal of Hepatology, 94 healthy adults drank 80 grams of sugar per day — roughly two cans of soda — for seven weeks, assigned to fructose, sucrose, glucose, or no sugary drink at all. The result was specific: fructose and sucrose roughly doubled the rate at which the liver manufactured new fat, measured as the fractional secretion rate of newly synthesized fatty acids (median 19.7%/day on fructose and 20.8% on sucrose, against 9.1% in the control group). The same 80 grams of glucose did not.

And here is the part most coverage leaves out: the same trial found no change in peripheral lipolysis, which the authors read as an absence of adipose-tissue insulin resistance over that period. Seven weeks of two sodas a day did not break these participants' insulin sensitivity. What it did was switch on the liver's fat factory.

That distinction is the whole point. "Sugar causes insulin resistance" is a slogan. "Sugar-sweetened drinks roughly double hepatic fat synthesis within weeks, and the sugar type determines whether it happens" is a finding — and it is the honest version of what people mean when they say these products wreck your hormones.

This article is educational, not medical or nutrition advice. Sakred Health is not affiliated with or endorsed by any company named here. Every figure comes from a named peer-reviewed source.

Key statistics at a glance

• Basal fractional secretion of newly synthesized fatty acids: 19.7%/day on fructose, 20.8% on sucrose, 9.1% in controls — a roughly two-fold increase — while glucose produced no change — Geidl-Flueck et al., Journal of Hepatology, 2021
• The same trial found no change in peripheral lipolysis and no change in total fatty acid or plasma free fatty acid oxidation, indicating that several weeks of sugary drinks did not induce adipose-tissue insulin resistance — Geidl-Flueck et al., 2021
• Each additional daily serving of sugar-sweetened beverage is associated with roughly 27% higher relative risk of type 2 diabetes in pooled prospective cohorts — observational — dose–response meta-analysis of prospective studies
• Sugar-sweetened beverages are linked in a large body of evidence to weight gain and higher risk of type 2 diabetes, cardiovascular disease and some cancers — Malik & Hu, Nature Reviews Endocrinology, 2022
• Beverages supply roughly half of all added sugars in US adults' diets — USDA, What We Eat in America / NHANES
• The American Heart Association's daily added-sugar limits are 25 g for women and 36 g for men — a single 12-oz cola exceeds the women's limit on its own

What the trial actually did

The design is what makes this worth reading. Ninety-four participants were randomized into four groups and given drinks sweetened with one of three sugars, or none, on top of their usual diet for seven weeks. It was double-blind — neither participants nor researchers knew which sugar was in which drink — which matters enormously in nutrition research, where expectation shapes reported outcomes.

The three sugars are chemically distinct in a way that turns out to be decisive:

• Glucose is absorbed and used throughout the body; nearly every cell can burn it.
• Fructose is metabolized largely in the liver.
• Sucrose — table sugar — is a glucose molecule bonded to a fructose molecule, so it delivers both.

Glucose is missing from that chart for a reason: it did not move the measure. Same grams of sugar, same calories, same seven weeks — and the metabolic consequence depended on which molecule was in the glass.

That is a genuinely important result, because it means "sugar" is not one exposure. The fructose half of table sugar is doing the work, and virtually every sweetened beverage on the market delivers it, whether the label says sucrose, high-fructose corn syrup, cane sugar, agave, or fruit juice concentrate.

What the trial did not find

We are going to spend a section on the negative result, because it is the part that gets stripped out when this study is cited online.

Insulin sensitivity did not measurably collapse. Rates of peripheral lipolysis — fat release from adipose tissue, which rises when adipose tissue becomes insulin resistant — did not differ between groups. Neither did total fatty acid oxidation or plasma free fatty acid oxidation. The authors' own reading is that several weeks of sugary drinks does not induce adipose-tissue insulin resistance.

So if you have read that two sodas a day will make you insulin resistant within weeks, this trial is evidence against that specific claim, not for it.

What the researchers describe instead is a first metabolic change: elevated basal hepatic fat synthesis, which they characterize as a plausible early step toward longer-term metabolic problems rather than as damage already done. That is a mechanism with a plausible trajectory, not a diagnosis.

Two limits worth naming. The participants were healthy young adults, so the result may not transfer to people who are older, insulin resistant already, or metabolically compromised. And seven weeks is seven weeks — it is long enough to reveal a switch being flipped and far too short to show where the road leads.

The long-run evidence, graded honestly

For the long run there are no randomized trials, because you cannot randomize people to drink soda for twenty years. What exists is prospective cohort data, and it is consistent: each additional daily serving of sugar-sweetened beverage is associated with roughly 27% higher relative risk of type 2 diabetes, with similar signals for weight gain and cardiovascular disease summarized in Malik and Hu's 2022 review in Nature Reviews Endocrinology.

Grade that correctly. Observational data cannot establish cause. People who drink more soda differ systematically in income, physical activity, overall diet quality, sleep and healthcare access, and statistical adjustment never fully removes those differences. Relative risk is also not absolute risk — a 27% increase on a small baseline is still a small number.

What makes this body of evidence more persuasive than most nutritional epidemiology is that it now has a mechanism attached. The cohort studies say heavy soda drinkers get more diabetes. The controlled trial shows a specific, dose-delivered, sugar-type-dependent metabolic change that plausibly connects the two. Neither alone would be convincing. Together they are hard to wave off.

Why "it spikes your insulin" is the wrong frame

Insulin rising after you eat is not pathology. It is the system working — insulin's job is to move glucose out of the blood and into cells, and every carbohydrate-containing food triggers it, including the ones nobody worries about.

We looked into this while writing about seasonal drinks and had to correct ourselves: the popular claim that liquid sugar spikes blood glucose harder than solid food is not well supported when macronutrients are matched. The defensible difference is satiety — 250 calories of soda does not reduce subsequent eating the way 250 calories of food does — plus, per this trial, what the liver does with fructose specifically.

So the useful questions are not about spikes. They are: how much added sugar arrives in a day, how much of it is fructose, and does it come with anything else — fiber, protein, fat — or on its own. Our food chart sorts common items on that basis, and the added-sugar disclosure gap explains why the first of those questions is often unanswerable at a counter.

What this looks like in a real drink

The drinks people actually order carry these doses without looking like an experiment. A Grande Pumpkin Spice Latte carries about 32 grams of added sugar; a Starbucks Chai Latte 29 grams of total sugars; a Pumpkin Cream Cold Brew 31. The trial's 80-gram daily dose is two or three of those.

None of that makes a single latte harmful. It makes the daily one worth counting, which is a different and much less dramatic claim than the internet usually makes.

Frequently asked questions

Do sugary drinks cause insulin resistance?

Not on the timescale usually claimed. A seven-week double-blind trial giving 94 adults 80 grams of sugar daily found no evidence of adipose-tissue insulin resistance. It did find that fructose and sucrose roughly doubled the liver's production of new fat, which researchers describe as an early metabolic change rather than established damage.

Is fructose worse than glucose?

For this outcome, yes. In the same trial, at identical doses, fructose and sucrose doubled hepatic fat synthesis while glucose produced no change at all. Since sucrose is half fructose, ordinary table sugar and high-fructose corn syrup both deliver it.

Does soda cause type 2 diabetes?

Prospective cohort studies associate each daily serving with roughly 27% higher relative risk, but those are observational and cannot prove cause. The controlled trial evidence supplies a plausible mechanism, which strengthens the case without closing it.

Is fruit juice as bad as soda?

Fruit juice delivers fructose in liquid form without the fiber of whole fruit, so on the mechanism above it is closer to soda than to fruit. Whole fruit is a different exposure: the sugar arrives inside a fiber matrix and in far smaller quantities per serving.

How much added sugar is too much?

The American Heart Association sets 25 grams a day for women and 36 for men. A single 12-ounce cola exceeds the women's limit on its own, and beverages supply roughly half of all added sugars in the American diet.

Sources

• Journal of Hepatology — Geidl-Flueck et al., Fructose- and sucrose- but not glucose-sweetened beverages promote hepatic de novo lipogenesis: A randomized controlled trial (2021)
• Nature Reviews Endocrinology — Malik & Hu, The role of sugar-sweetened beverages in the global epidemics of obesity and chronic diseases (2022)
• Diabetes Care — Malik et al., Sugar-Sweetened Beverages and Risk of Metabolic Syndrome and Type 2 Diabetes: A Meta-analysis (2010)
• PMC — Consumption of sugar sweetened beverages, artificially sweetened beverages and fruit juices and risk of type 2 diabetes, hypertension, cardiovascular disease, and mortality: a meta-analysis
• American Heart Association — Added Sugars

Related: Do Ultra-Processed Foods Make You Eat More? and What Big Food Doesn't Have to Tell You About Sugar.