Sugar, Diet Drinks, and “That Copenhagen Study”: What the Paper Really Found

This article breaks down the sugar vs diet drinks study so you can see what actually changed and how to use it in real life.

You might have heard a spicy claim doing the rounds: a “famous Copenhagen study” supposedly showed cola drinkers gained 10 kg, water drinkers lost 2 kg, and diet-soda drinkers gained 2 kg.

We looked up the actual paper (PMID: 22205311). It doesn’t say that.

Here’s what the real 6-month randomized trial found when people drank 1 litre per day of either sucrose-sweetened cola, diet cola, milk, or water:

  • Body weight: No significant difference between groups over 6 months. In other words, the study did not show cola drinkers packing on 10 kg or water drinkers losing weight just by changing the drink. PubMed

  • Where fat was stored: The sugar-sweetened cola group had much bigger increases in liver fat, visceral (belly) fat, and muscle fat than the other groups. That matters for long-term health. PubMed+1

  • Blood markers: The sugar-cola group also saw higher triglycerides and total cholesterol. Diet cola behaved similarly to water for most outcomes. Milk and diet cola reduced systolic blood pressure versus regular cola. PubMed

So, did the study “prove” cola makes you gain 10 kg? No. It showed that what you drink can change where you store fat and your cardiometabolic risk markers, even if the bathroom scale doesn’t budge much.

TL;DR: Sugar-sweetened drinks increased ectopic (organ and belly) fat and blood lipids. Diet drinks looked a lot like water in this trial. Weight change alone didn’t tell the full story. PubMed

Sugar vs Diet Drinks Study: Key Results. Why this matters (and why headlines get it wrong)

  • Weight change is only part of the picture. Where you store fat—especially liver and visceral fat—is strongly linked to health risk. This trial used imaging to quantify those depots, which is a big strength. PubMed

  • Diet drinks aren’t magic, but they can be a useful swap. Across several Copenhagen projects using the same design, diet beverages tracked closer to water for risk markers when compared with sugar-sweetened drinks. PubMed+2PubMed+2

  • Milk wasn’t a villain here. In this trial, it didn’t produce the same adverse ectopic-fat/lipid profile as sugar cola. (Different question from individual lactose tolerance or preferences.) PubMed

What to do with this info (simple, practical swaps)

At Green Gym Group we care less about online drama and more about what helps you day-to-day:

  1. If you drink sugary fizzy drinks most days, swap most of them for water, diet/zero versions, or sparkling water. You’ll likely improve blood lipids and reduce “organ fat” over time—even before the scale moves. PubMed

  2. Keep total calories and protein on track. Changing drinks helps, but overall diet quality (protein, fibre, fruit/veg) and energy balance still drive body composition.

  3. Think in averages, not absolutes. A full sugar drink occasionally won’t derail your progress. It’s the daily patternthat counts.

Common questions we get in the gym

“Do diet drinks spike insulin the same as sugar?”
Not in this 6-month work: the adverse changes were seen with sugar-sweetened cola. Other controlled trials from the same Danish group suggest no worse insulin sensitivity with diet drinks vs milk or water over similar time frames. Context and overall diet still matter. PubMed

“So is sugar the only problem?”
No. Sleep, steps, training, fibre, and overall calories all matter. But if you’re drinking sugar daily, swapping that habit is one of the highest-leverage changes you can make.

“If my weight isn’t changing, does it matter?”
Yes—because where fat is stored matters for long-term risk. That’s exactly what this imaging study showed. PubMed

Quick takeaways from the Copenhagen trial

  • Sugar-sweetened cola: ↑ liver fat, ↑ visceral fat, ↑ muscle fat, ↑ triglycerides, ↑ total cholesterol. PubMed

  • Diet cola: similar to water on most outcomes; lower systolic blood pressure than regular cola. PubMed

  • Milk: did not replicate the sugar-cola risk pattern in this trial; also reduced systolic blood pressure vs regular cola. PubMed

  • Body weight: no significant differences between groups over 6 months (so the “+10 kg” claim is false). PubMed

How we coach this at Green Gym Group Kemptown, Brighton.

  • Start with the easy wins: swap most sugary drinks for water or zero/diet.

  • Build a plate that works: protein + carb + colour (+ fibre) at each meal.

  • Train 2–3×/week: full-body strength sessions; add steps or short cardio on off days.

  • Track what matters: trend weight, waist, and how you feel (energy, sleep, training). Scales don’t catch organ fat changes quickly—habits do.

If you want help turning this into a weekly plan, pop in for a chat. We’ll meet you where you’re at—no scare tactics needed.

Quick Q&A

  • Are diet drinks “worse than water”?
    Not in this 6-month trial. Risk markers tracked closer to water than to sugar cola.
  • If my weight didn’t change, does it matter?
    Yes. Ectopic fat (liver/visceral) and lipids changed meaningfully in the sugar-cola group—even without big scale changes.
  • So should I drink diet soda all day?
    No. Hydrate with water first, use diet/zero mainly as a swap for sugary drinks.

Sources

  • Maersk et al., 2012 (American Journal of Clinical Nutrition): “Sucrose-sweetened beverages increase fat storage in the liver, muscle, and visceral fat depot: a 6-mo randomized intervention study.” Key results summarized above. PubMed+1

  • Bruun et al., 2015: Secondary analysis from the same trial cohort (uric acid outcomes). PubMed

  • Engel et al., 2018: Long-term comparison of milk, sugar-sweetened, and non-caloric beverages on insulin sensitivity markers. PubMed