Is Sugar Bad for Your Kidneys?

Type 2 diabetes is the single biggest cause of chronic kidney disease in the UK, accounting for around a third of all dialysis starts. High sugar intake drives weight gain and insulin resistance, which over years can progress to type 2 diabetes and diabetic kidney disease.

High sugar intake also independently raises blood pressure (the second biggest cause of CKD), raises uric acid (a risk factor for kidney stones and gout), and contributes to non-alcoholic fatty liver disease (which is increasingly linked to CKD).

So even in non-diabetic adults, cutting added sugar protects kidneys through multiple pathways.

UK guidance (Scientific Advisory Committee on Nutrition, SACN 2015) recommends:

• Adults and children aged 11+: ≤ 30 g free sugars/day (~ 7 teaspoons).
• Children 7–10: ≤ 24 g/day.
• Children 4–6: ≤ 19 g/day.
• Under 4s: avoid added sugar where possible.

'Free sugars' = sugars added to food and drink + sugars naturally present in honey, syrups, fruit juice and smoothies. It does NOT include sugars naturally present in whole fruit, vegetables or milk (lactose).

A 330 ml can of standard cola contains ~ 35 g sugar — more than the daily limit in one drink. A large glass of orange juice (250 ml) contains ~ 22 g sugar. Most flavoured yoghurts contain 15–20 g per pot. Reading labels matters.

Large cohort studies consistently show that sugar-sweetened beverages — fizzy drinks, sweetened squashes, sweetened teas, energy drinks, sweetened coffee shop drinks — are the dietary item most strongly linked to faster CKD progression.

Key findings:

• UK Biobank (2020s): ≥ 1 can/day of sugar-sweetened drink associated with significantly faster eGFR decline and ~ 60% higher risk of incident CKD over 10 years.
• US Nurses' Health Study: dark cola drinks (≥ 2 cans/day) associated with ~ 2x higher risk of CKD.
• Multiple smaller studies have linked high sugar-sweetened drink intake to higher kidney stone risk.

The practical implication: if you drink sugar-sweetened drinks daily, replacing them with water (or unsweetened tea/coffee) is one of the highest-impact dietary changes you can make for kidney health.

Fructose is metabolised differently from glucose. The liver handles almost all of it, and the metabolic pathway produces uric acid as a byproduct. Diets very high in fructose (especially as high-fructose corn syrup in soft drinks) can raise serum uric acid.

Why this matters:

• Higher uric acid increases the risk of gout flares.
• Higher urinary uric acid increases the risk of uric-acid kidney stones.
• Some observational studies link higher uric acid to faster CKD progression, though randomised trials of uric-acid-lowering treatment have been mixed.

Whole fruit contains fructose too, but the fibre slows absorption and there is no evidence that normal whole-fruit intake increases kidney stone or CKD risk. The problem is concentrated liquid fructose, not apples.

Switching from sugar-sweetened to artificially-sweetened drinks helps with weight, diabetes and blood pressure — all good for the kidneys, and likely a net positive in most cases.

But: large recent observational studies have linked very high intake of artificial sweeteners (aspartame, sucralose, acesulfame K) to worse cardiovascular and metabolic outcomes. The findings are observational and the absolute risk increases are small, but they do suggest 'diet' drinks are not a free pass.

Practical hierarchy:

1. Water (still or sparkling) — best.
2. Unsweetened tea or coffee — fine.
3. Diet/zero-sugar fizzy drinks — better than full-sugar versions; treat as occasional rather than all-day defaults.
4. Sugar-sweetened drinks — minimise.

Highest-impact changes:

• Stop sugar-sweetened drinks. Replace with water, sparkling water, unsweetened tea or coffee.
• Cap fruit juice at 150 ml/day (NHS counts this as one of your 5-a-day, but no more than once).
• Eat whole fruit rather than smoothies (smoothies count as free sugars beyond 150 ml; whole fruit doesn't).
• Read the label on breakfast cereals — many are 20–35% sugar; aim for ≤ 5 g sugar/100 g.
• Watch flavoured yoghurts, granola, cereal bars and 'health' drinks — often surprisingly high.
• Reduce sugar in tea and coffee gradually if you take it — most people stop noticing after 2–3 weeks.
• If you have diabetes, work with your diabetes team — sugar reduction often allows reductions in medication too.