Coke Zero and other zero-sugar soft drinks have become popular alternatives to traditional sugary beverages, particularly among people concerned about weight and metabolic health. With fatty liver disease now affecting approximately one in three UK adults, many wonder whether these artificially sweetened drinks might contribute to liver problems. Whilst sugar-sweetened beverages are a well-established risk factor for non-alcoholic fatty liver disease (NAFLD), the relationship between zero-sugar alternatives and liver health is less clear. This article examines the current evidence on Coke Zero and fatty liver, exploring what the science tells us about artificial sweeteners, liver health, and practical dietary approaches.

What Is Fatty Liver Disease?

Fatty liver disease, medically termed hepatic steatosis, occurs when excess fat accumulates in liver cells. In the UK, this condition affects approximately one in three adults and represents a growing public health concern. The liver normally contains some fat, but when fat is present in 5% or more of liver cells (hepatocytes), it is considered pathological.

There are two main categories of fatty liver disease. Alcohol-related liver disease (ARLD) develops due to excessive alcohol consumption over time and encompasses a spectrum from simple steatosis through hepatitis to cirrhosis. Non-alcoholic fatty liver disease (NAFLD), now increasingly referred to as metabolic dysfunction-associated steatotic liver disease (MASLD), occurs in people who drink little or no alcohol. NAFLD is strongly associated with metabolic syndrome, including obesity, type 2 diabetes, high blood pressure, and dyslipidaemia.

In its early stages, fatty liver disease typically causes no symptoms and is often discovered incidentally during imaging for other conditions or through risk-based case-finding in primary care. Many people with NAFLD have normal liver enzyme levels on blood tests. However, if left unaddressed, it can progress to more serious conditions. Non-alcoholic steatohepatitis (NASH) involves inflammation and liver cell damage alongside fat accumulation. Over years or decades, this may advance to liver fibrosis, cirrhosis, or even hepatocellular carcinoma.

Diagnosis may begin with elevated liver enzymes (ALT, AST) on blood tests, but NICE guidance emphasises risk-based assessment in people with obesity, type 2 diabetes, or metabolic syndrome, even when liver function tests are normal. Ultrasound imaging can detect steatosis, though it may miss milder cases. To assess the degree of liver scarring (fibrosis), NICE recommends offering the Enhanced Liver Fibrosis (ELF) blood test to adults with NAFLD. An ELF score of 10.51 or above indicates likely advanced fibrosis and warrants referral to a liver specialist. Transient elastography (FibroScan) may be used in secondary care as part of specialist assessment. Early detection and lifestyle modification remain the cornerstone of management, as no specific pharmacological treatment is currently licensed in the UK for NAFLD.

Can Coke Zero Cause or Worsen Fatty Liver?

Coke Zero and similar zero-sugar soft drinks do not contain the free sugars found in regular sugar-sweetened beverages. This is significant because excessive consumption of free sugars, particularly fructose, is a well-established risk factor for developing NAFLD. Fructose is metabolised primarily in the liver and can promote de novo lipogenesis—the conversion of carbohydrates into fatty acids—leading to hepatic fat accumulation.

There is currently no direct clinical evidence from human trials that zero-sugar soft drinks cause fatty liver disease. These products contain artificial sweeteners (primarily aspartame and acesulfame potassium in Coke Zero) rather than sugar, and these do not undergo the same metabolic pathways that contribute to hepatic steatosis. However, the relationship between artificial sweeteners and metabolic health remains an area of active research and some scientific debate.

Some observational studies have suggested associations between diet soft drink consumption and metabolic syndrome components, including obesity and insulin resistance—both risk factors for NAFLD. However, these studies cannot prove causation, and confounding factors are significant. People who consume diet drinks may already have metabolic concerns or unhealthy dietary patterns that independently increase fatty liver risk.

The key consideration is overall dietary pattern rather than isolated beverage choices. Whilst zero-sugar drinks eliminate the direct sugar load that contributes to liver fat, they do not provide nutritional benefit. The World Health Organization's 2023 guidance recommends against using non-sugar sweeteners for long-term weight control, as they do not appear to offer sustained metabolic advantages. Regular consumption of any sweetened beverages—whether sugar or artificially sweetened—may perpetuate preferences for sweet tastes and potentially displace healthier options like water. For individuals with existing NAFLD or metabolic risk factors, focusing on whole dietary quality, rather than simply substituting sugar with artificial sweeteners, represents the most evidence-based approach to liver health.

Artificial Sweeteners and Liver Health: What the Evidence Shows

Artificial sweeteners, including aspartame, acesulfame potassium, sucralose, and saccharin, have been extensively studied for safety and are approved for use in the UK by the Food Standards Agency (FSA) and the European Food Safety Authority (EFSA). These substances provide sweetness without the caloric load of sugar and do not directly raise blood glucose levels.

Regarding liver health specifically, the evidence remains limited and somewhat contradictory. Animal studies have produced mixed results. Some rodent research has suggested that certain artificial sweeteners might influence gut microbiota composition, glucose metabolism, and inflammatory markers—factors theoretically relevant to NAFLD development. However, these studies often use doses far exceeding typical human consumption and may not translate directly to clinical practice.

Human epidemiological data is largely observational and cannot establish causation. Some cohort studies have found associations between diet soft drink consumption and increased risk of metabolic syndrome, weight gain, and type 2 diabetes—all NAFLD risk factors. However, reverse causality and residual confounding are significant concerns: individuals already at metabolic risk may choose diet drinks in an attempt to manage their health, creating a spurious association.

Randomised controlled trials—the gold standard for evidence—have not demonstrated that artificial sweeteners directly cause liver damage or fat accumulation in humans at normal consumption levels. Systematic reviews of available human trial data have found insufficient evidence to conclude that non-nutritive sweeteners adversely affect liver enzymes or hepatic steatosis at typical intakes, though data specifically examining NAFLD endpoints remain limited.

The European Food Safety Authority and UK Food Standards Agency maintain that approved sweeteners are safe within acceptable daily intake (ADI) levels. The ADI represents an amount that can be consumed daily over a lifetime without appreciable health risk. For aspartame, this is 40 mg per kilogram of body weight daily. To put this in context, a 70 kg adult would need to consume a very large quantity of diet soft drinks daily to approach this level, though the exact number varies by product formulation. The ADI is set with a substantial safety margin and is intended as a lifetime average, not a daily threshold.

Important safety note: People with phenylketonuria (PKU) must avoid aspartame, as it provides phenylalanine, which they cannot metabolise safely. Products containing aspartame carry a warning label for this reason.

Current evidence does not support the claim that moderate consumption of artificially sweetened beverages directly causes fatty liver disease in humans, though research continues and long-term data remain incomplete.

Diet and Lifestyle Changes to Support Liver Health

For individuals with NAFLD or those at risk, evidence-based lifestyle modification remains the primary therapeutic approach. NICE guidance and international liver societies emphasise that even modest weight loss can significantly improve hepatic steatosis and associated metabolic parameters.

Weight management is paramount. Studies demonstrate that losing 7–10% of body weight can reduce liver fat, improve inflammation, and even reverse early fibrosis. This should be achieved through sustainable caloric restriction combined with increased physical activity, rather than extreme or fad diets. A Mediterranean-style dietary pattern—rich in vegetables, fruits, whole grains, legumes, nuts, olive oil, and fish—has shown particular benefit for liver health in clinical trials, independent of weight loss.

Specific dietary recommendations include:

• Reducing added sugars and refined carbohydrates: Limit sugar-sweetened beverages, confectionery, biscuits, and processed foods high in free sugars

• Increasing fibre intake: Aim for at least 30g daily from vegetables, fruits, whole grains, and pulses, in line with the NHS Eatwell Guide

• Choosing healthy fats: Replace saturated fats with unsaturated sources like olive oil, nuts, and oily fish

• Limiting alcohol: UK Chief Medical Officers advise that to keep health risks low, it is safest not to drink more than 14 units per week on a regular basis. For people with NAFLD, particularly those with fibrosis, your doctor may recommend drinking less or abstaining entirely

• Adequate protein: Support muscle mass and metabolic health with lean meats, fish, eggs, and plant proteins

Physical activity provides benefits beyond weight loss. UK Chief Medical Officers' guidelines recommend at least 150 minutes of moderate-intensity aerobic activity weekly, plus muscle-strengthening exercises on two or more days per week. Both aerobic and resistance training can reduce liver fat, even without significant weight reduction.

Beverage choices matter. Water should be the primary drink. Whilst replacing sugar-sweetened drinks with zero-sugar alternatives eliminates a major source of excess calories and free sugars, the optimal approach is reducing reliance on sweetened beverages altogether. Unsweetened tea and coffee (observational evidence suggests coffee may be associated with reduced liver fibrosis progression, though this requires further study) and water with natural flavouring (lemon, cucumber, mint) are preferable long-term choices.

Managing comorbidities is also important. Statins are safe and recommended for people with NAFLD who have dyslipidaemia or elevated cardiovascular risk; they do not worsen liver disease and may offer some hepatic benefit. Your GP can advise on appropriate medication for type 2 diabetes, hypertension, and cholesterol management. Regular monitoring ensures appropriate adjustment of management strategies.

When to Seek Medical Advice About Fatty Liver

Fatty liver disease is often asymptomatic in its early stages, making opportunistic detection during routine healthcare encounters important. However, certain circumstances warrant proactive medical consultation.

You should contact your GP if you:

• Have risk factors for NAFLD (obesity, type 2 diabetes, metabolic syndrome) and have not had recent liver assessment

• Receive abnormal liver enzyme results (elevated ALT, AST, or GGT) on blood tests

• Experience unexplained persistent fatigue, particularly if accompanied by other symptoms

• Notice discomfort or a sensation of fullness in the right upper abdomen

• Have a family history of liver disease

• Are taking medications that may affect the liver and have concerns about monitoring

Seek urgent medical attention by calling 999 or attending A&E if you develop:

• Jaundice (yellowing of skin or eyes)

• Severe abdominal pain or swelling (ascites)

• Confusion or altered mental state (hepatic encephalopathy)

• Vomiting blood or passing black, tarry stools

• Easy bruising or bleeding

These symptoms may indicate advanced liver disease or acute liver injury requiring immediate assessment. For urgent but non-emergency concerns, contact NHS 111 for advice.

Your GP will typically arrange initial investigations including liver function tests, viral hepatitis screening, and possibly an abdominal ultrasound. NICE guidance recommends offering the Enhanced Liver Fibrosis (ELF) blood test to adults with NAFLD to assess for advanced fibrosis. An ELF score of 10.51 or above indicates likely advanced fibrosis and warrants referral to a hepatologist or specialist liver clinic. Referral is also appropriate if you have suspected cirrhosis, persistently abnormal liver function tests without clear cause, or complex management needs.

Regular monitoring is important for those diagnosed with NAFLD. NICE recommends repeating the ELF test every three years in adults with NAFLD to detect progression. You should have at least annual review with your GP to assess cardiovascular risk factors, weight, and metabolic control. Depending on your individual risk profile, you may need more frequent blood tests or imaging. Your healthcare team can provide personalised advice on diet, exercise, weight management, and medication optimisation.

Early engagement with healthcare services allows for timely intervention, potentially preventing progression to more serious liver disease. NAFLD is largely manageable through lifestyle modification when detected early, emphasising the importance of not delaying medical consultation when concerns arise.

Frequently Asked Questions